Responses of spinal cord neurons to systematic changes in hindlimb skin temperatures in cats and primates. Single-neuron recordings were made from the lumbar spinal cords of cats and squirrel monkeys. Recording sites were distributed throughout the dorsal horn and included Rexed's laminae I and III-VI in both species and laminae VII-VIII in cats. Activity was studied during systematic changes in skin temperature over the range of 15-49 degress C; this encompasses the perceptions of innocuous cooling and warming plus the initial stages of noxious heating. The experiment included studies in which the thermal stimulus was changed from various preadapting temperatures. In all cases, the sensitivity of an individual neuron to changes in skin temperature was associated with responses to various intensities of tactile stimulation which, for some neurons, could range from low to painful pressures. More than two-thirds of the neurons excited by innocuous temperature changes discharged to both cooling and warming, although the thresholds were much lower for cold temperature differecnes (less than or equal to 2 degrees C for cold steps as compared with more than 6 degrees C for warm steps). However, many neurons only responded to extreme cooling or, more frequently, noxious heating. The temperature response relationships of many neurons during cooling was best described in reference to specific cold-receptor activity because the discharge rates declined at extremely cold temperatures and because the slopes of the temperature-response functions were nearly identical when studied with different adapting temperatures. The responses of certain slowly adapting mechanoreceptors was considered in describing some of the spinal cord activity during extreme cooling. The responses to hot temperatures were attributed to activity in various receptors, including especially polymodal receptors. Activity during innocuous warming was ascribed to one population of peripheral warm receptors that do not show maximal static activity during innocuous warm stimuli. The significance of the extensive convergence in the spinal cord from mechanoreceptors and thermoreceptors was discussed in relation to thermal perception and the complexity of the information transmitted by the spinothalamic tract.


Organization of cat striate cortex: a correlation of receptive-field properties with afferent and efferent connections. The purposes of this study were 1) to relate the receptive-field characteristics of area 17 cells to their afferent and efferent connections, and 2) to obtain quantitative data from area 17 neurons for later comparison with area 18 cells. Intra- and extracellular recordings were obtained in paralyzed preparations which were anesthetized with nitrous oxide. The connectivities of the recorded cells were determined from responses to electrical stimulation of afferent and efferent pathways. In parallel to the classification of units as simple and complex cells, the receptive fields were grouped in four classes according to the spatial arrangement of on- and off-areas; class I, fields with exclusive on- or off-areas; class II, fields with spatially separate on- and off-areas; class III, fields with mixed on-off areas; class IV, fields which could not be mapped with stationary stimuli. The results from electrical stimulation suggest two major classes of cells: cells in the first group are driven mainly or exclusively by LGN afferents. They rarely receive additional excitation from intrinsic or callosal afferents and rarely possess corticofugal axons. Cells in the second group receive either converging inputs from LGN afferents and further intrinsic afferents or only from intrinsic afferents. They frequently received additional input from callosum and from recurrent collaterals of corticofugal axons. They project subcortically more often than cells in the first group. Cells in both groups can be driven either by X- or Y-type afferents. Cells in the first group have mainly class I and class II fields or simple fields, whereas the neurons in the second group have mainly class III and class IV fields or complex fields. Thus, simple and complex cells differ in their connectivity patterns, but the discriminative parameter is neither the selective connection to the X- or the Y-system nor, in a strict sense, the synaptic distance from subcortical input. From the combined consideration of receptive-field properties and connectivity patterns it is concluded that class I and class II cells or simple cells are concerned mainly with the primary analysis of subcortical activity, whereas class III and class IV cells or complex cells perform a correlative analysis between highly convergent activity from extrinsic and intrinsic afferents.


Cat parastriate cortex: a primary or secondary visual area. The purpose of this study was to determine to what extent the cat parastriate cortex processes afferent geniculate activity in a way similar to that in area 17. The area explored was located on the lateral gyrus between the Horsley-Clarke coordinates A1 to 4 and L3 to 4. The receptive-field properties of area 18 cells and their responses to electrical stimulation of afferent and efferent pathways were measured with the same methods as described previously in area 17. Mutual correlations among these items were calculated and compared with the respective data from area 17. The results of this correlative analysis revealed numerous similarities between the two areas with regard to their afferent and efferent connections and their intrinsic organization. Consequently, the structure of the receptive fields and their numerical distribution resembled those in area 17. The same was true for the correlations between receptive-field parameters and afferent and efferent connectivity. The main differences were that area 18 cells had larger receptive fields and responded to considerably higher stimulus velocities. It is suggest-d that these differences are caused by the fact that area 18 receives subcortical afferents of the Y-type, whereas the dominant input to area 17 comes from the X-system. It is concluded that the area investigated in this study is organized in parallel to area 17 and deals with other aspects of visual information than area 17.


Modification of auditory and somatosensory system activity during pupillary conditioning in the paralyzed cat. The role of sensory systems in the development of behavioral conditioned responses was investigated by recording multiple-unit activity in the auditory and somatosensory pathways during Pavlovian conditioning of the pupillary-dilation responses of paralyzed cats. Establishment of conditioned pupillary-dilation responses to a white noise CS+, pupillary discrimination between the CS+ and a tone CS-, and subsequent discrimination reversal provided the behavioral foundation for examining neural changes related to behavioral learning. Multiple-unit responses to the acoustic CS+ were significantly enhanced in the auditory cortex, cochlear nucleus, and somatic cortex, but not in the cuneate nucleus. The possibility that these effects could be due to changes in stimulus intensity at the sensory receptor, to mo-ement artifacts, or to feedback from skeletal responses were ruled out because the animals were immobilized. Nor could these neural changes be attributable to sensitization, as those brain areas which showed conditioned enhancement to the CS+ exhibited significantly larger responses to the CS+ than to the CS-. Furthermore, the changes in neural activity followed the significance of the CS; after reversal of the reinforcement contingencies, the amount of multiple-unit activity evoked by the stimuli gradually reversed too. Although the somatic cortex showed conditioning and discrimination, greater stimulus specificity was found in the auditory system. Only in the somatic cortex was there a significant increase in responses to the CS- as well as the CS4. Furthermore, both somatosensory loci exhibited enhanced responses to those tactile probes presented during the acoustic CS, suggesting a phasic increase in neural excitability to all stimuli. Analysis of the number of trials required to attain an acquisition criterion indicated that the neural changes occurred first in the auditory cortex, then the cochlear nucleus, followed in turn by the somatic cortex, and finally the cuneate nucleus. However, none of these neural changes preceded acquisition of conditioned pupillary dilations. These results suggest that sensory system changes are not essential for the initial associative process. These findings indicate that the study of autonomic conditioned responses may prove beneficial in seeking the critical neural events which underlie the initial association between two stimuli. A hypothetical model, which explains the development of pupillary and sensory system conditioned responses, was also presented.


Intracellular recordings from different types of medullary respiratory neurons of the cat. Respiratory neurons were recorded intracellularly within the lateral region of the lower brain stem of vagotomized and artificially ventilated cats. Bulbospinal, vagal, and antidromically nonresponsive types of neurons were distinguished by means of vagal and intraspinal stimulation. Almost all types of neurons discharged a burst of action potentials during one of the two phases of the central respiratory cycle, as indicated by phrenic nerve activity. The discharge pattern of the different types of neurons were described. The origin of the spntaneous changes of the membrane potential was investigated by measurements of the reversal potentials and membrane conductance changes. The results reveal that both inspiratory and expiratory types of neurons receive an excitatory input during their discharge period, and a reciprocal inhibitory input during their silent period. In addition, one type of neuron was described which receives inhibitory inputs during both inspiration and expiration. Recurrent inhibition, as indicated by hyperpolarizing postsynaptic potentials and membrane conductance changes following the antidromic action potential seems to exist only within the network of the vagal neurons. Suggestions are made about the functional organization of the neuronal network of the medullary respiratory system and the mechanism generating its rhythmic activity.


Accommodative reactions of medullary respiratory neurons of the cat. In most of the bulbospinal respiratory neurons, threshold depolarization increased during the early period of their spontaneous burst discharge but decreased again at the end of a burst. In some vagal respiratory neurons, however, threshold depolarization increased steadily until the very end of their discharge period. These changes generally were accompanied by changes in the rate of depol1rization of the spikes, the amplitude of their overshoot, and their discharge frequency. For a given synaptic input, as indicated by the constancy of the interspike membrane potential trajectories, threshold depolarization of bulbospinal neurons remained constant or even decreased. Only in some vagal neurons was an increase in threshold deplarization observed under these conditions. With the exception of some vagal neurons, most of the respiratory neurons did not show a pronounced accommodative behavior when stimulated with linear rising currents. When stimulating with current pulses, all neurons discharged repetitively with only slight adaptation, which was already complete by the first few spike intervals. The current-frequency relationship was linear and revealed a primary and secondary range. The results support neither accommodation nor adaptation as important mechanisms in the genesis of the rhythmic activity of respiratory neurons.


Modulation of synaptic effectiveness of Ia and descending fibers in cat spinal cord. 1. In the unanesthetized spinal cord, conditioning stimulation of low-threshold afferents (below 1.3 times threshold strength) in the biceps semitendinosus (BST) nerve often reduced the peak amplitude of the monosynaptic Ia EPSPs evoked in gastrocnemius motoneurons without affecting the monosynaptic component of the EPSPs evoked by stimulation of the ipsilateral ventral funiculus (VF) in the thoracic cord. 2. Volleys to the BST nerve comprising higher threshold afferents (usually above 1.4 times threshold strength) reduced the peak amplitude of the monosynaptic Ia and VF EPSPs and shortened their falling phase. 3. Conditioning volleys to low-threshold cutaneous afferents often increased the Ia-EPSP peak amplitude, sometimes without affecting the monosynaptic component of the VF EPSP. 4. In most cases the Ia nd VF monosynaptic EPSPs elicited in a given motoneuron summated nonlinearly. The amount of nonlinear summation between Ia and VF monosynaptic EPSPs was often reduced by low-threshold BST conditioning volleys. These observations suggest that in many instances, both species of fibers end in "electrotonically close" synaptic loci over the motoneuron surface. Therefore, amplitude changes of monosynaptic Ia EPSPs produced by conditioning afferent volleys without concomitant changes of monosynaptic VF EPSPs do not appear to result from postsynaptic remote conductance changes and may be attributed to a presynaptic mechanism. 5. At the time of occurrence of the Ia and VF monosynaptic EPSP the variance of the motoneuron membrane potential may be increased above base-line levels with a time course approximately matching the EPSP itself. Conditioning stimulation of BST afferents usually reduced Ia EPSP variance, often without affecting or even increasing the variance of the monosynaptic VF EPSPs. These observations provide additional evidence that Ia EPSP variability is introduced, at least in part, through the segmental pathways mediating primary afferent depolarization. 6. The possibility of a differential control of the information flow transmitted through two independent channels converging on a given cell ensemble is discussed.


Inferior colliculus. I. Comparison of response properties of neurons in central, pericentral, and external nuclei of adult cat. The responses of 150 units in the central (ICC), pericentral (ICP), and external nuclei (ICX) of the inferior colliculus of the anesthetized cat were studied in relation to their tuning characteristics and binaural responses to tonal stimuli. Units in ICC were characterized by sharp tuning and binaural responses, while those in ICP and ICX were frequently very broadly tuned with a poorly defined best frequency. Nonetheless, in the latter nuclei a tendency existed for tonotopic organization to occur with high frequencies located externally and low frequencies at the margins of the central nucleus. Tuning measurements were hampered by the common occurrence of habituation in the discharges of single units in ICP and, to a lesser extend, ICX. The majority of units in ICP could be differentiated from those in ICX by their monaural input. Speculations were advanced linking anatomical cell types to physiological responses in the three nuclei and into the possible functional significance of the different behavior of units to tonal stimuli.


Inferior colliculus. II. Development of tuning characteristics and tonotopic organization in central nucleus of the neonatal cat. Tuning curves were measured for 65 units in the inferior colliculus of seven anesthetized kittens aged from 6 to 28 days. At 2 days of age the inferior colliculus was divisible into central, pericentral, and external nuclei. Evidence was found for broader tuning curves to occur in the pericentral nucleus compared with the central nucleus, as has been observed in the adult. The middle ear was filled with serous fluid to 6 days, while the external auditory meatus remained collapsed until 10 days. Central nucleus tuning curves in kittens were relatively flat with high thresholds. Best-frequency thresholds diminished from a mean of near 100 dB SPL at 6-11 days to near 50 dB in the adult. The marked drop in thresholds between days 22 and 21 led to the adoption of the sharp form of tuning curve common for adults. Tonotopic organization of the central nucleus was clear at day 11. Speculations were advanced about the dependence of central auditory maturations on cochlear development, axon myelination in the auditory pathway, and changes in synaptic density as a function of age.


Tendon organs of cat medial gastrocnemius: responses to active and passive forces as a function of muscle length. The responses of 13 Golgi tendon organs to graded force development of 29 motor units in medial gastrocnemius of the cat have been studied in five experiments. Of the 13 tendon organs, 11 were responsive to passive stretch within the physiological range of muscle length and 5 were "spontaneously" active at very short lengths where no passive tension could be recorded. The relationship between passive force and the firing rates of the various afferents ranged from a linear one to a power relation (Y = Axb + c) with b, a widely varying exponent. Results support the general conclusion that although many Ib afferents respond to passive force within the physiological range of muscle stretch, this form of stimulus is not a particularly effective one. The statis responses of Golgi tendon organs to active force development produced by single motor units was studied at different muscle lengths. In all cases the apparent sensitivity (change in firing rate per active force developed) decreased as muscle length approached Lo. The static responses of Golgi tendon organs to force developed by single motor units were also studied during fatiguing contractions. The data suggest a sigmoid relationship between force developed at the tendon and the Ib response. The collective response of all 13 tendon organs to active and passive forces at different muscle lengths was also examined. This analysis offered further support for the viewpoint that active motor unit contractions provide themost significant excitatory input to tendon organs and that changes in passive force during muscle stretch have comparatively little effect on the collective tendon organ response. The interaction between active and passive force inputs to the Golgi tendon organs is discussed in relation to the complicated nature of the relationship between forces measured at the tendon and those acting within the receptor capsule. When these complications were taken into account it was possible to explain the differences in responsiveness of a given tendon organ to active contraction of several motor units and to passive force in terms of a single force-firing rate curve for the receptor. It is concluded that changes in the force of contraction of single motor units result in relatively small changes in Ib afferent firing and that during normal muscle contractions, changes in the number of motor units acting on a single receptor must produce far more significant changes in firing rate than changes in the amount of force developed by any single unit. Changes in dynamic Ib sensitivity to single motor unit contractions are also shown to depend on length and in a similar way to the changes in static Ib sensitivity. During fatiguing contractions, a sigmoid relation was found between the dynamic Ib response and the rate of force development by single motor units.


Physiologic characteristics of vestibular first-order canal neurons in the cat. I. Response plane determination and resting discharge characteristics. The response plane and resting rate characteristics of first-order, vestibular, semicircular canal neurons were studied in 67 cats under sodium pentobarbital anesthesia using single-unit recording techniques in the eighth nerve. Five hundred fifty-nine units were classified as to the canal they were associated with by employing an identification technique based on physiologic response patterns to brief, high-level (up to 250 degrees/S2) angular accelerations delivered in various head positions. All horizontal canal neurons had increased firing rates to ampullopetal and all vertical canal units to ampullofugal endolymph flow. The average observed roll and pitch null points for each canal were used to determine the average sensitivity vectors for the right horizontal, anterior, and posterior canals. These sensitivity vectors were at a variance of 4.6-10.2 degrees from those predicted by anatomical measurements (3). The mean resting discharge characteristics of 318 first-order neurons was 36.0 spikes/s (range 0.50-114 spikes/s). No significant difference was noted between horizontal and anterior canal neurons on horizontal and anterior canal neurons on the basis of resting rate. The resting rate of the posterior canal neuron population was significantly lower. The regularity of the resting discharge varied in all three canals and the average coefficient of variation was 0.238 for the population, with a range of 0.298-1.030. The population distribution of all resting-rate statistical parameters appeared to be unimodal, indicating that first-order canal neurons may not be broken into discrete populations on the basis of resting-rate characteristics. Of 47 adequately examined first-order canal neurons, 25 demonstrated a repeatable and predictable alteration in their resting discharge as their position to gravity was reoriented. This alteration was usually nonadapting and varied in magnitude according to the degree of tilt and original starting position. Of 25 canal gravity units, 4 had nearby units from the same canal which were unresponsive to gravity, suggesting the effect was due to a limited distortion of the crista or cupula rather than an overall displacement of the cupula.


Accumulation of 99mTc-glucoheptonate in acutely infarcted myocardium. The distribution of 99mTc-glucoheptonate in normal mice and its accumulation in acutely infarcted myocardium were studied in animals. Rapid blood clearance and low concentration of the tracer in normal myocardium were found in tissue distribution studies performed in mice. Experimental myocardial infarction was performed in nine dogs. Four hours after the intravenous injection of 99mTc-glucoheptonate the uptake ratio of the myocardial infarcted area to normal myocardium was 20:1; to blood, 9:1; and to lung, 6:1. The greatest concentration of radiopharmaceutical in the infarcted tissue was noted in areas that had 20-40% of normal perfusion. Regions of infarction were clearly defined by external gamma scintigraphy. Clinical investigation of this tracer in humans appears warranted.


Accumulation of 99mTc-diphosphonate in malignant pleural effusions: detection and verification. Increased accumulation of radioactivity was observed in two cases of malignant pleural effusions during the performance of routine bone scans with 99mTc-diphosphonate. This previously unreported finding was verified both qualitatively and quantitatively by appropriate scanning and laboratory techniques.


Liver-heart imaging in evaluating hepatic focal defect. An edge defect in the superior area of the left lobe is difficult to evaluate on the liver image. Eighty normal liver-heart images showed no focal separation between liver and heart images. Four cases with suspicious edge defects in the superior area of the left lobe were also studied with liver-heart imaging. One case was well demonstrated to be due to right ventricular compression of the liver without focal separation of the liver-heart images. Three cases showed focal separation of the liver-heart images. One defect was diagnosed as amebic abscess and showed enlargement on the followup images. The other two cases were proven to have liver metastasis. Liver-heart imaging is a reliable technique in evaluating a suspicious defect in the superior area of the left lobe of the liver.


Scintigraphic appearance of bifrontal epidural hematoma: case report. A bifrontal and parasagittal epidural hematoma was detected on the brain scan. The scintigraphic appearance of this rare lesion is described.


Hepatic artery-portal vein fistula detected on hepatic flow study: case report. A man with a history of gunshot wounds presented with jaundice and a bruit over the upper abdomen. The radionuclide flow sequence revealed simultaneous perfusion of the liver with transit of the activity down the aorta. The was considered compatible with a fistula between the hepatic artery artery and portal vein (confirmed angiographically and at autopsy). An expanding aneurysm of the hepatic artery produced an enlarging focal parenchymal defect.


Radionuclide scintigraphy: a diagnostic aid in delayed traumatic splenic rupture: case report. The use of 99mTc-sulfur colloid scintigraphy in the diagnosis of a delayed traummatic splenic rupture 10 days after injury is described. Splenic scintigraphy of patients falling in this category may help the clinician in the early detection of splenic rupture.


Radionuclide studies in hemangioendotheliomatosis: case report. Multiple abnormal radionuclide studies of brain, lungs, kidneys, liver, and spleen were observed in a patient with hemangioendotheliomatosis.


Inconsistent images of thyroid nodule scintigrams made with iodine and pertechnetate: case report. In a patient with Hürthle cell adenoma, thyroid scans showed nodular trapping of 99mTc-pertechnetate, but nodular binding of 131I was not observed.


Functioning metastases in liver from thyroid carcinoma: case report. Radioiodine uptake in liver metastases was observed in two patients with follicular carcinoma of the thyroid.


The fate of four 75Se-labeled amino acids: studies of some unsuccessful pancreas-scanning agents. The Radiochemical Centre developed a number of alpha-amino acids labeled with 75Se in the hope of finding a pancreas-scanning agent superior to L-selenomethionine. Six were submitted for clinical trial and we tested four of these: D-selenomethionine and three derivatives of selenocysteine. Dynamic scintillation camera studies showed that liver uptake was substantial in all cases but that the time course of accumulation and removal differed between agents. Plasma radioactivity curves demonstrated differences in initial removal rates. Two of the agents showed evidence of incorporation of activity into protein and release into the circulation just as with L-selenomethionine. Whole-body counter measurements showed that the retention of activity from the agents exhibiting early plasma protein incorporation was similar to that of L-selenomethionine. Much of the activity from the other two agents was excreted faster but small proportion was retained for a long time. Although the cummulated activity and absorbed dose were substantially less for at least two of the agents than for 75Se-L-selenomethionine, the lack of sufficient pancreatic concentration renders them inferior as scanning agents.


Improvement of scintigram reliability by isocount scanning and multilevel analysis. Given the target source conditions and the detector parameters, the isocount scanning uses optimally the available observation time by maintaining the statistical reliability of each measurement in the composition of a scintigram and by devoting all the observation time to the region of interest through logic circuits which allows quick skipping of the background region. The multilevel analysis is an effective enlargement of the dynamic range of the displayer screen density characteristics that emphasizes small uptake ratios in any density level. It also makes the features extraction very easy by producing an animated sequence of pictures of the observed organ on the screen. The detectability of small uptake ratios significantly improved, specially in regions of low counting rate where the fluctuation of data severely degrades the picture quality in the conventional constant speed scanning method.


The distended gastric fundus: simulation of a left suprarenal mass. A discrete region of low or absent activity in the left suprarenal area, simulating an avascular mass on renal imaging or radionuclide angiography, can result from dilatation of the gastric fundus.


Potential errors in the radioassay of 125I. The radioassay of very small 125I samples in both conventional and side-hole well crystals has been investigated. Using a multichannel analyzer, the source was counted at various positions within these well crystals. The effect of using a single-channel pulse-height analyzer was simulated by summing the counts over a 24-keV range across the primary peak, over a 30-keV range across the sum-coincidence peak, and over a 56-keV range across both peaks. In all crystals the primary peak was independent of sample position within the well over a range of several centimeters. The contribution of the sum-coincidence peak varied significantly with sample position in the conventional well crystals. With the side-hole crystal the counts contributed by the sum-coincidence peak exhibited a 2-cm plateau.


Measurements of the effective thyroxine ratio (ETR) in the neonate, infant, and child. The applicability of the effective thyroxine ratio (ETR) was assessed in euthyroid neonates, infants, and children. ETR determinations on cord blood fell within the normal adult range. In contrast, ETR values of newborns age 4 hr to 2 days were all elevated (1.17 -1.37) and within the hyperthyroid range for adults. Values in infants age 2 weeks and older and in children age 1-15 years all fell within the normal adult range. These findings suggest that the ETR can be used as an ancillary measure of thyroid function in infants and children. In the immediate postpartum period, however, ETR values may be normally in the adult hyperthyroid range.


Multidirectional tomagraphy of defects in the facial canal. An experimental investigation. Defects on the tympanic wall of the facial canal may endanger the nerve in middle ear surgery. Their preoperative tomographic demonstration is therefore valuable. In an experimental investigation an attempt was made to assess the discernibility of artificial defects of different size by hypocycloid and spiral tomography of temporal bone specimens (both isolated and mounted in a tissue-equivalent skull phantom). The thickness of the wall was measured and its influence on the discernibility of the defects discussed.


Patency of ventriculo-atrial shunt determined radiologically. A radiologic method for assessment of the patency of ventriculo-atrial shunts is described together with a safe technique for gas encephalography of patients with ventriculo-atrial shunt. Despite discontinuity the shunting system may be functioning.


Filtration in soft tissue radiography.

Filtration in soft tissue radiography. The influence of K-edge filters in combination with tungsten target tubes has been analysed in the low voltage range. It appears that these filters do not offer any advantages with this target material. Al-filtration, applicable to different types of soft tissue radiography of joints is discussed.


Quantitative long-term determinations of the alveolar bone mineral mass in man by 125I absorptiometry. III. Effect of experimental dental plaque formation. Gingivitis was induced in young adults who refrained from all oral hygiene measures during a three week period. No significant alterations concerning the mineral mass of the subjacent alveolar bone could be demonstrated.


Spectral variation of the conversion factor of an image intensifier. The conversion factor of the image intensifier Sirecon duplex 25/15 was investigated by means of a videodensitometer for varying values of the tube potential and varying filtering of the radiation. It was found that the conversion factor can be increased by Cu filtering. By analysis of the measurement data, the spectral variation of the conversion factor was determined. The conversion factor has a maximum for 60 keV photons and falls rapidly for photons of energy below 45 keV. By the method described, the spectral response function of an image intensifier can be determined experimentally without the use of a spectrometer.


Physical characteristics of barium contrast media and their influence on roentgen image information. Various barium contrast media intended for radiographic examinations of the colon were analysed in a plastic model. This model contained fixed test objects which could be identified and counted on the films thus providing a measure of image information obtainable. Particular attention was paid to the marked differences in sedimentation of the various contrast media and the manner in which these affected image information.


Angiography and hemodynamic measurements in extensive soft tissue trauma to the extremity. The early circulatory changes following extensive soft tissue injury to the hind leg of the dog was examined by angiography and by measurement of blood flow by an electromagnetic flowmeter. The trauma caused a marked increase of blood flow and vasodilatation in the injured extremity with or without combination of a fracture. The later gradual increase of calculated vascular peripheral resistance was angiographically reflected by successively impaired flow in peripheral arteries. In spite of the decrease of flow, the dilatation of the larger arteries persisted for several hours.


Radiologic heart volume from 100 mm photofluorograms. Radiologic heart volume could be calculated in 1 188 (94%) of a sample of 1 263 male civil servants over the age of 40. The chest films were taken under the conditions of massminiture radiography with no subject preparation and an unmodified Odelca 100 mm unit. Estimates of observer variability are reported an 'normal values' for a free-living population given. A method of calculating a correction factor for image magnification and subsequent reduction in size is described, and evidence presented that each Odelca unit has a unique correction factor.


Improved brain scan specificity utilizing 99mTc-pertechnetate and 99mTc(Sn)-diphosphonate. Each of 36 patients was studied with two separate brain scans performed sequentially after the injection of 20 mCi of 99mTc-pertechnetate or 20 mCi of 99mTc(Sn)-diphosphonate. The resulting scans were qualitatively compared, and lesion-to-nonlesion ratios of activity determined. Diagnoses were established by clinical criteria and were supported in the majority of cases by computerized axial tomography or roentgen angiography or both. Histologic confirmation was available in five cases of tumor and in the single cases of subdural hematoma and cerebral abscess. Of 22 cerebral infarctions, 15 were better demonstrated with 99mTc-(Sn)-diphosphonate than with 99mTc-pertechnetate. Of the seven remaining cases, three were visualized equally well with each agent, and three were better demonstrated with 99mTc-pertechnetate. One was not seen with either agent. Of the 12 tumors, 11 were visualized better with 99mTc-pertechnetate than with 99mTc-(Sn)-diphosphonate while in one case the lesion was seen equally as well with both agents. In no case was a lesion definitely seen with one radiopharmaceutical and not with the other. These results indicate that this dual method is helpful in differentiating gliomas and metastases from cerebral infarctions.


Improved diagnosis of "nondelineated" thyroid nodules by oblique scintillation scanning and echography. The scan of the thyroid gland in oblique projections has enabled us to visualize 11 "cold" thyroid nodules which were not delineated on a traditional anterior view among 825 patients studied in a 2-yr period. Accurate localization of the nodule in the oblique projection facilitated accurate placement of the transducer for echography. The combination of the isotope imaging studies and ultrasound then permitted one to differentiate solid and cystic "cold" nodules. Diagnosis and choice of therapy are therefore enhanced by the addition of oblique views, when needed, and echography.


Unilateral ventricular reflux: case report. Reflux of 131I-human serum albumin with a dilated ventricle from the contralateral ventricle was observed in a patient with an abnormal cisternogram.


Technetium-99m-pyridoxylideneglutamate: a new hepatobiliary radiopharmaceutical. II. Clinical aspects. Technetium-99m-pyridoxylideneglutamate (99mTc-PG) is a nontoxic radiopharmaceutical that was found to undergo rapid biliary excretion in normal humans. The biliary tree and gallbladder were seen within 10-15 min of injection and by 20 min marked accumulation of radioactivity was noted in the gallbladder and gastrointestinal tract. Of ten "control" volunteers, seven had normal 99mTc-PG-cholescintigrams. In the remaining three, the gallbladder was not visualized. Gallbladder disease was not excluded in these three subjects. Of 24 patients referred for investigation of right upper quadrant abdominal pain, 13 proved to have gallbladder disease. All seven patients with acute cholecystitis and one of four patients with chronic cholecystitis had nonvisualization of the gallbladder on the cholescintigram whereas five patients with chronic cholecystitis or cholesterolosis had normal cholescintigrams. Six of the eight patients with nonvisualization of the gallbladder on cholescintigram had contrast radiologic studies (oral cholecystogram or intravenous cholangiogram or both), and in all six, nonvisualization of the gallbladder was also reported on the contrast study. cholescintigraphy was found to be greatly inferior to contrast radiologic studies in the detection of gallbladder stones. Eleven patients had complete extrahepatic biliary obstruction and this diagnosis was correctly made in all 11 by the cholescintigram. Fourteen patients had incomplete extrahepatic biliary obstruction. The correct diagnosis was made on the cholescintigram in seven but in the remaining seven it was not possible to distinguish between incomplete extrahepatic biliary obstruction and hepatocellular disease. Malignant lesions (carcinomas of head of pancreas, gallbladder, common bile duct or ampulla of Vater) were the cause of obstruction in 10 of the 25 patients with complete or incomplete obstruction and the diagnosis of obstruction due to malignancy was correctly made in 8 of these 10 by means of a scintigraphic equivalent to Courvoisier's sing. Finally, 11 patients had hepatocellular disease and a nonspecific pattern consistent with either imcomplete biliary obstruction or hepatocellular disease was observed on the cholescintigram in all 11. The 99mTc-PG cholescintigram is suggested for a role complementary to that of contrast radiologic studies in the preoperative investigation of patients with possible surgical disease of the biliary tract. Contrast radiologic techniques are advocated as being more appropriate in the nonjaundiced patient with suspected gallbladder disease whereas the 99mTc-PG cholescintigram is advocated as being more appropriate in the patient with jaundice. The value of the 99mTc-PG cholescintigram lies in the confidence with which complete extrahepatic biliary obstruction can be diagnosed. The "scintigraphic Courvoisier's sign" seems a useful indicator of malignant obstruction.


Bone marrow imaging using 111In-citrate: 111In-kinetics in the pelvic region. When bone marrow scintigraphy was performed using 111In-citrate, radioactivity was observed in the pudendal region. Subsequently, the kinetics of 111In in the pelvic region after intravenous administration of 111In-citrate for bone-marrow scanning in 14 patients was examined. On the first day, radioindium was found predominantly in the large pelvic blood vessels and in the pudendal region. In all male patients, the scrotal area was affected with both testes presumably delineated in two patients. In the female patients little radioindium was detected in the pudendal region, most probably in the vulva; distinct radioactivity was found in the pelvis although the ovaries could not be identified. In the following period the 111In uptake in the bone marrow increased considerably and reached its maximum usually 24 hr after the injection. Because a distinct radiation dose from 111In to the gonads cannot be excluded on the basis of our scintigraphic findings and the absorbed dose has not yet been estimated sufficiently, judgment should be used for the present if 111In-citrate is applied for bone marrow imaging.


Xenon-133, 127Xe, and 125Xe for lung function investigations: a dosimetric comparison. Of the possible radionuclides of xenon, 127Xe and 125 Xe have better physical properties for lung function measurement than 133Xe. A comparison of the radiation doses for these three radionuclides has been made for a typical scintillation camera investigation. Using an exponential model for washin and washout of gas, it is shown that the specific activity-time relationship is always equal to the product of the spirometer concentration and the rebreathing period. It is concluded that of the three radionuclides 127Xe gives the lowest radiation dose during a typical lung function study.


Basal ganglia scans in the human.

Basal ganglia scans in the human. Using a 64Cu complex, we obtained human basal ganglia scans in three normal volunteers and in one patient with Wilson's disease with an oral dose of 1 mCi. The method with this new radioactive compound was simple and safe and the results were very encouraging.


Dual-channel facilitation of the 99mTc radiocardiogram. A refinement of the radionuclide-angiocardiogram is described using a low deadtime scintillation camera and hardwire data storage, processing, and display system for the purpose of anatomic definition of the passage of a radioactive bolus through the carciopulmonary circulation by dual-channel, dual-color, subtraction methodology. The summation of the bolus pathway is displayed as a static frame of reference for the sequential kinetic image. The technique is noninvasive and employs 15 mCi of 99mTc pertechnetate. This procedure may be employed as the conventional bolus study for determining the cardiac kinetics ordinarily obtained by the method. The opportunity of viewing the bolus position in relation to its entire pathway significantly facilitates defining the multiple areas of interest the observer may wish to study.


Evaluation of cold areas on the thyroid scan with 67Ga-citrate. Cold areas on 131I or 99mTc thyroid scans were re-evaluated using 67Ga-citrate in 134 patients. In 62 patients surgical specimens were obtained for histologic studies. Of 46 benign lesions, all had negative 67Ga scans, and 67Ga scans in 5 of the 16 lesions judged to be malignant were positive. It was thought that the sensitivity of the method did not warrant its use for routine screening in evaluations of malignancy of thyroid nodules.


Labeling of erythrocytes with 103Ru-ruthenium red. The preparation of 103Ru-ruthenium red and its use in the labeling of erythrocytes is described. Since in vivo and electrophoretic studies indicate that the tag is firmly bound to the cell, this technique appears to be very convenient for spleen scintigraphy and for the study of the in vivo fate of tagged cells.


Causal attributions as a function of locus of control, initial confidence, and performance outcomes. Causal attributions and body movements indicative of tension were recorded while subjects completed an anagrams task that was more extensive than most similar tasks used in attribution studies. Nine trials each containing 10 anagrams were presented such that most subjects succeeded on three sets of relatively simple anagrams, failed on three sets of difficult anagrams, and either succeeded or failed on three sets of intermediately difficult anagrams. Attributions and body movements were predicted by a combination of locus of control, initial confidence, and type of outcome. High-confident internals attributed responsibility for outcomes to themselves more than did low-confident externals, and this difference was most prominent when subjects failed. Tension-indicating body movements were also less common among the former than the latter subjects and were in greater evidence with failure than with success. The data indicate that there is consistency between locus of control and causal attributions obtained during performances. The data also correspond to the findings on helplessness in which aversive agents prove to be more deleterious when individuals perceive themselves as unable to alter their negative circumstances.


Trait and other sources of variance in the S-R inventory of anxiousness. The S-R Inventory of Anxiousness has a reliability of .95 but shows only 5% of its variance due to persons (traits). This strange combination of results is explored logically and empirically. A distinction is made between the Inventory as a test and as an experimental design. Some characteristics and problems of the Inventory as an experimental design are examined. These problems suggest that it is unwarranted to include variance from situations and modes of response in the total variance against which the component of variance due to individual differences is evaluated. It is such inclusions that have yielded the result of 5% of variance due to persons. It is concluded that results from the Inventory, when generalized to other omnibus inventories of anxiety, do not have the drastic implications that have been previously claimed.


Long-term value change initiated by computer feedback. To determine whether value change can be induced by a computer rather than a human agent and whether value change can be induced even when target values are not preselected for experimental treatment, subjects first filled out the Rokeach Value Survey and then obtained information from a computer enabling them to compare their own value rankings with those previously obtained for various reference groups. Experimental subjects exposed to computer feedback showed, first, significant changes in value systems 2 months afterward whereas control subjects showed no such changes. Second, value system change was significantly greater among those experimental subjects whose value rankings were on the whole more discrepant from those of positive reference groups. Third, rankings of certain values concerning achievement, peace, and egalitarianism were affected in a 2-month period following the treatment. These findings are interpreted within a broader theoretical framework about the conditions leading to long-term cognitive and behavioral change.


Pain cues and uncertainity as determinants of aggression in a situation involving repeated instigation. In contrast to the Buss aggression paradigm, a situation was employed in which subjects were given an expanded range of response options and were exposed to instigation throughout their response period. It was found that (a) despite these changes pain cues depressed aggressiveness in the present situation as they generally do in the Buss paradigm, but that this effect only occurred where the subjects' aggression was initially ineffective in changing their target's behavior; (b) situational uncertainity, which is minimal in a Buss-type situation, was related to aggressiveness; (c) subjects tended to match rather than attempt to control the responses of the target; and (d) the present paradigm is capable of isolating a personality variable related to overall aggressiveness. These data are discussed in terms of other recent paid cue studies that deviate from the standard Buss situation. Generally, the findings suggest the potential of increasing the range of situations in which aggression is studied.


Defensive externality and blame projection following failure. This study focuses upon the relationship between internal-external control and defensive blame projection. Trust was used as a moderator variable for making differential predictions concerning the behavior of two subgroups of externals: defensive externals, whose externality is presumed to reflect primarily a verbal technique of defense, and congruent externals, whose externality reflects a more genuine belief that most outcomes are determined by forces beyond their personal control. As predicted, defensive externals showed a stronger tendency than did congruent externals and internals to resort to blame projection following failure at an achievement task. There were no group differences in attribution following task success. Defensive externals were found to be more responsive to negative feedback than were congruent externals.


Cognitive flexibility in hypnosis: response to change communication from the hypnotist. It was predicted that modification of response as it indexes cognitive flexibility in the hypnotic subject is related to susceptibility to hypnosis and the difficulty of the hypnotic task attempted. Experiment 1 isolated two distinct hypnotic tasks (easy and difficult); alternative forms of each item conveyed either clear or unclear structure concerning the response that was perceived as most appropriate. In Experiment 2, 101 subjects were administered hypnotic induction procedures and tested for modification of response on both items; for each subject, the hypnotist posed a conflict in communication by plausibly requesting an alteration in response from the behavior that the subject had chosen to indicate previously. Change data demonstrated that hypnotic subjects modified their behavior in hypnosis, but their cognitive flexibility was much more relevant to easy than to difficult tasks. Results highlight a further dimension of role enactment as well as the special role cognitive skills in play in our understanding of performance on hypnotic test items.


Informational determinants of females' self-attributions and observers' judgments of them in an achievement situation. A female (A) received feedback about both her own and a male or female other's (B's) performance on an achievement task, and then estimated the likelihood that she and B possessed each of several attributes related to competence, likeableness, and physical attractiveness. The situation was witnessed by a male or female observer who then judged B's attributes and predicted A's and B's ratings of one another. A formulation of social inference processes developed by Gollob was used to identify and compare the informational cues used by actors and observers in making these attributions. The contributions of these cues depended substantially on the type of attribute being inferred, the judge (A or the observer), and whether the judgment was made of A or of B. A's behavior (i.e., her performance on the achievement task) contributed less to her self-attributions than it did either to her predictions of how B would rate her or to observers' actual judgments of her attributes. A's self-attributions tended to be relatively more influenced by her experiences before participating in the experiment. Whereas A appeared to use B's performance as a comparative standard when judging her own competence and expected B to do likewise, observers did not use B's performance in this manner when judging A. Moreover, A did not use her own performance as a standard when judging attributes of B. The article discusses theoretical implications of these results for attribution and self-perception processes.


Temperature dependence of the circulation pattern in the upper extremities. 1. The rate of blood flow D through the hand and the rate of heat H transferred by that blood flow into the hand were measured on eleven subjects between 18 and 22 years old. The hand was immersed in water, at temperatures ranging from 10 to 40 degrees C. 2. The rate of blood flow was measured with a water-air displacement plethysmograph, which was adapted also to give heat loss measurements. 3. Comparison of the relative values of D and H at different temperatures gives information about the change in distribution of blood flow with temperature. On decreasing water temperature, the change in distribution starts at about 25 degrees C and continues gradually to about 15 degrees C, suggesting that more and more blood is shunted to deep veins. For one of the subjects, no change in distrubiton pattern was found.


Potassium activation in Helix aspersa neurones under voltage clamp: a component mediated by calcium influx. 1. Helix aspersa neurones under voltage clamp generate prolonged outward currents (potassium currents) in response to depolarizing command pulses. 2. The potassium currents recorded from cell A were reversibly reduced 25-50% by 10 mM cobalt ions in the bathing medium; 1 mM lanthanum, 10(-6) g/ml. D-600 and 10(-6) g/ml. iproveratril had similar effects but were only partially reversible. 3. The relationship between the potassium currents and the membrane potential had an "n" shape in normal saline. In calcium-free saline (containing 25 mM magnesium) the potassium currents were reduced and the "n" shape was abolished. The effect of calcium-free saline was readily reversible. 4. The voltage-dependence of the calcium-sensitive potassium currents was similar to that of the "late" calcium channel in squid axons (Baker, Hodgkin & Ridgway, 1971). 5. When cell A was depolarents were made up of two exponentially declining components. The slower of the two components was reduced in calcium-free saline. 6. When cell A was depolarized by 150 mV for 10 msec and then repolarized the "tail" currents were made up of a single rapidly declining component. The reversal potential of this component changed by 58 mV for a tenfold change in the external potassium concentration as predicted by the Nernst equation. 7. The reversal potential of "tail" currents having both components was less sensitive to changes in the external potassium concentration. 8. Tetraethylammonium (TEA) ions blocked both calcium dependent and voltage sensitive potassium currents. Each receptor was found to bind a single molecule of TEA. The dissociaton constant was about 10 mM in each case. 9. The intracellular concentration of ionized calcium was estimated from the potential at which there was no apparent calcium influx (the null point). It was between 3 x 10(-8) M and 8 x 10(-8) M with 10(-2) M calcium in the bathing medium. 10. The null point changed 30 mV for a tenfold change in the external calcium concentration as predicted by the Nernst equation. 11. It is concluded that depolarization of Helix neurones activates two typesof potassium channel. One channel is voltage dependent and highly selective for potassium. Activation of the other channel is dependent on the influx (or injection, see Meech, 1972, 1974a) of calcium. This calcium mediated potassium activation system saturates at high external calcium concentrations and is inhibited by external magnesium ions.


Calcium and sodium ions as charge carriers in the action potential of an identified snail neurone. 1. The soma of cell A in Helix aspersa produced action potentials in sodium-free or calcium-free saline, but not in saline with neither sodium nor calcium. 2. The axon had a sodium-dependent action potential. 3. Tetrodotoxin (5 x 10(-6) M) had no effect on the overshoot except at low external divalent ion concentrations. 4. The action potential in sodium-free saline was blocked by cobalt. 5. The slope of action potential overshoot against sodium concentration in the presence of 10 mM calcium was 10.5 mV/tenfold change. That of overshoot against calcium concentration in the presence of 75 mM sodium was 22 mV/tenfold change. 6. In sodium-free saline the slope of overshoot versus calcium concentration was 27 mV/tenfold change. 7. It is concluded that calcium is an important charge carrier in the action potential of cell A.


Voltage-clamp studies of the calcium inward current in an identified snail neurone: comparison with the sodium inward current. 1. Membrane currents were recorded under voltage clamp from cell A of the snail Helix aspersa. 2. In sodium-free saline the inward current was reduced to 75% of that in normal saline (containing both sodium and calcium). 3. The inward current in sodium-free saline was dependent on the external calcium concentration. 4. Calcium-free saline reduced the inward current to 30% of that in normal saline. (Na, Ca)-free saline abolished the inward current. 5. Changes in calcium concentration shifted the curve relating calcium conductance to membrane potential along the voltage axis. 6. Inactivation of inward current in both normal saline and sodium-free saline developed exponentially with time. 7. Steady-state inactivation of calcium inward current was similar to that for sodium current and it is concluded that the conductance mechanisms for these two ions bear a close resemblance.


The effect of procaine on the action of acetylcholine at the neuromuscular junction. 1. The effect of procaine on acetylcholine-induced membrane fluctuations (ACh noise) was studied by intracellular and focal external recording from end-plates of frog sartorius muscle. 2. With intracellular recording, ACh noise (the ratio of variance to mean depolarization) was substantially reduced by procaine, suggesting a greatly decreased amplitude of the elementary potential change. 3. Spectral analysis of the ACh noise indicated a dual average time course of the underlying "shot effects", similar to the complex shape (brief spike followed by a long tail of low intensity) of the end-plate current in pro-aine-treated muscle. 4. The post-synaptic blocking action of procaine can be largely explained by the drastic shortening of the initial high-intensity phase of the end-plate conductance change. 5. The average time course of the ACh shot effects is discussed in terms of alternative hypotheses, one attributing the complex shape to each elementary event, the other involving sequential reaction steps which produce two unequal populations of ion gates of different "life-times".


The development of functional innervation in the hind limb of the chick embryo. 1. The development of functional motor innervation was studied in the hind limb of chick embryos from Stages 25 to 43 by observing contraction of individual muscles and by recording the resultant tension when individual spinal nerves were electrically stimulated. 2. At later developmental stages (35-43) a given muscle always received functional innervation from specific spinal nerves. This pattern, with respect to the craniocaudal position of motoneurones, was similar to those described for amphibians and mammals. 3. The observed pattern was similar throughout development from the time that movement could first be elicited at Stages 27-28. There was no indication that motoneurones form initial synapses with inappropriate muscles. 4. Recordings from muscle nerves during excitation of individual spinal nerves gave results similar to the tension recordings, showing that even at early developmental stages muscle nerves did not contain substantial numbers of inappropriate axons. 5. Most limb muscles or primitive muscle masses became functionally innervated at the same time with no clearly defined proximo-distal sequence of limb innervation. 6. It appears that chick motoneurones are initially specified with respect to their peripheral destination and grow out selectively to synapse with appropriate muscles from the outset.


Synaptic potentials recorded from neurones of the submucous plexus of guinea-pig small intestine. 1. Intracellular recordings have been made from neurones lying in the submucous plexus of guinea-pig mid small intestine. 2. Most neurones in this plexus receive an extensive excitatory input which could be abolished by tubocurarine. 3. A proportion of neurones also received a single inhibitory input which was activated by transmural stimulation. 4. Some of the characteristics of the inhibitory potentials evoked by transmural stimulation are described. 5. The observations are discussed in relation to the concept of descending excitation (Hirst, Holman & McKirdy, 1975).


The relation between discrimination and sensitivity in the perception of motion in depth. 1. Binocular discrimination of the direction of a target's motion in depth was measured in terms of the smallest angular difference in direction that could be detected with a probability 50% better than chance. Directional discrimination was measured for targets moving along 16 different trajectories directed to the left and right of the nose. 2. The relative velocities of the retinal images in the left and right eyes gave a sensitive cue to the direction of the target's motion in depth. 3. The direction of motion was bets discriminated when the target moved along a line directed close to the nose. A change in direction of only 0.2 degrees from this direction of motion could be detected. Discrimination showed two other maxima, one on each side of the central maximum. Discrimination fell to about 0.6-0.8 degrees when the target's direction was changed by only 6 degrees to either side of the nose. 4. The curve of sensitivity to movement in depth had a generally inverse shape to the directional discrimination curve: sensitivity was minimal for trajectories directed near the nose and increased for trajectories directed so as to miss the head. 5. The directional discrimination curve can be related to the sensitivity curves of the four postulated neural mechanisms tuned to different directions of motion in depth; there are three discrimination maxima and, correspondingly, three trajectories for which the slopes of adjacent sensitivity curves differ maximally. This suggests that binocular psychophysical judgements of the direction along which a target moves in depth are to some extent mediated by neural mechanisms that compare (e.g. subtract) the outputs of directionally tuned movement detectors. One function of such neural comparators might be to enhance psychophysical sensitivity to the direction along which a target moves in depth, and thus to provide a physiological basis for precisely judging whether or not an object will hit the head. 6. We suggest that the neural basis for judging the direction of moving objects has an analogy in colour vision where opponent-colour mechanisms enhance sensitivity to wave-length differences in such a way that wave-lengths are more easily discriminated in those parts of the spectrum where the slopes of the pigment action spectra differ maximally.


An analysis of the representation of the forelimb in the ventrobasal thalamic complex of the albino rat. 1. Glass micro-electrodes have been used to record from a total of 998 units situated in the ventrobasal thalamic complex in the deeply anaesthetized albino rat. 2. Of these units 889 responded to electrical stimulation of the contralateral forelimb and fifty-one to the contralateral hind limb. The remaining units consisted of those with receptive fields on the trunk, head and those which responded to stimulation of more than one limb. Only the latter group of units showed any spontaneous activity in the absence of intentional stimulation. 2. Of the units which responded to electrical stimulation of the contralateral forelimb the receptive fields, modality and latencies of response were accurately determined for 505 units. The mean latency to supramaximal stimulation at the wrist was 4.49 (+/- 0.04 S.E. of mean) msec; and to mechanical stimulation (for 146 of these units) at the centre of the receptive field 6.58 (+/- 0.12) msec. The modalities were distributed as follows: light pressure, 391; heavy pressure, 47; hair movement, 40; claw sensitive, 15 and joint movement, 12 units. 4. The forelimb representation within the ventrobasal thalamic complex was somatotopically organized, the over-all appearance being that of an incompletely closed fist, palmar surface uppermost, thumb media, with the wrist caudal and the digital tips rostral and dorsal. 5. The central projection was distorted, some parts showing expanded representation, notably the tips of digits II and III and the medial wrist pad. Other parts were contracted, e.g. the wrist, forearm and shoulder. 6. Units with receptive fields consisting of the whole of a walking pad had shorter mean latencies, to tactile stimulation, than those whose field was a single spot on a pad. 7. Units were found to show an abolute unresponsive time to the second of a pair of identical supramaximal electrical stimuli of up to 50 msec, and a relative unresponsive time which could last up to 500 msec. The absolute unresponsive and relative unresponsive times to the second of a pair of tactile stimuli was shorter being 30 and 150 msec respectively. 8. The effect of decortication was to increase the excitability of thalamic units to peripheral stimulation both in the initial and later discharges.


Is brain prostaglandin synthesis involved in responses to cold? 1. Experiments with rats have suggested that prostaglandin synthesis in the C.N.S. may mediate thermoregulatory reactions to cold. This possibility was investigated in cats using two types of experiment. 2. In one series of experiments, c.s.f. collected from the cisterna magna of conscious cats exposed to a cold and a hot environment was assayed for prostaglandin-like activity. During cold exposure there was a slight increase in activity which persisted after return to neutral ambient temperature. There was no correlation between prostaglandin-like activity and rectal temperature. During the heat exposure there was no demonstrable change in activity. 3. In the second series, conscious cats were exposed to cold conditions and given intravenous injections of salicylate, paracetamol, or indomethacin, all of which inhibit prostaglandin synthesis. Indomethacin salicylate nor paracetamol caused any significant change in rectal temperature. 4. The results do not support a role for C.N.S. prostaglandin synthesis in thermoregulatory reactions to cold in cats.


Bronchial hysteresis in excised lungs.

Bronchial hysteresis in excised lungs. 1. Intrapulmonary bronchi in excised dog lungs were outlined with tantalum dust and stereoscopic radiographs taken during deflation and inflation of the lung with air, saline, Ringer or EDTA solutions. Dimensions of airways as a percentage of their values at full inflation were calculated from measurements of the stereoscopic X-ray images. 2. The mean deflation-inflation diameter difference at a transpulmonary pressure of 5 cm H2O was 20% in the air-filled lung, 9% in the saline filled preparation and 2% after filling with EDTA in saline. 3. These results show that the intrapulmonary bronchi have an intrinsic hysteresis separate from the hysteresis imposed on them by the expansion of the surrounding parenchyma. This intrinsic hysteresis is mainly due to the tone of the smooth muscle in the bronchial wall.


The velocity tuning of single units in cat striate cortex. 1. The activity of single units was recorded from the striate cortex (area 17) of anaesthetized, paralysed cats. Responses to stimuli moving at different velocities were examined. 2. Peak evoked firing frequency, rather than fotal evoked spikes, is used throughout as a measure of response. The former mea-ure gives curves of response vs. velocity that correlate well with curves of contrast sensitivity vs. velocity, wheras the latter does not. 3. Cortical receptive fields were classified according to the criteria of Hubel & Wiesel. Simple cells were found to prefer lower velocities (mean 2-2 deg sec-1) than complex cells( mean 18-8 deg sec-1). The response of simple cells to stimuli moving faster than 20 deg sec-1 is generally poor; complex cells usually discharge briskly to these speeds. 4. Cells classified as hypercomplex by the end-inhibition criterion were further chara-terized as type I or type II, according to the suggestion of Dreher (1972). Type I units are indistinguishable from simple cells in their velocity tuning, and type II units equally clearly resemble complex cells. These results are therefor consistent with Dreher's sbudivision. 5. Teh selectivity of cells for velocity is variable but can be quite marked. The average selectivities of simple and complex cells are not significantly different. There is an inverse correlation between preferred velocity and the sharpness of velocity selectivity for simple cells; no trend is apparent for other cell types. 6. No clear correlation is observed between the velocity preferances of units and their degree of direction selectivity, or receptive field arrangement. Simple cells with 'sustainef' temporal responses to flashed stimuli tend to prefer slower rates of movement than 'transient' ones, and to be less selective for velocity. 7. The results for different cortical cell-types are compared with the velocity tuning of X- and Y-cells in the lateral geniculate nucleus.


Effects of magnesium on contractile activation of skinned cardiac cells. 1. In the presence of a slight buffering of the free [Ca2+] with 0.050 mM total EGTA cyclic contractions were induced by a Ca2+-triggered release of Ca2+ on skinned (sarcolemma-free) segments of single cardiac cells from rat ventricle. The threshold of the free [Ca2+] trigger was elevated when the free [Mg2+] was increased. 2. At a suprathreshold free [Ca2+] increasing the free [Mg2+] resulted in a decrease in frequency and in an increase in amplitude of the phasic contractions. Addition of caffeine at a specified interval after a cyclic contraction produced a larger contraction when free [Mg2+] was higher. It was concluded that an increase of free [Mg2+] increased the capacity and the rate of binding for Ca2+ by the sarcoplasmic reticulum (SR). 3. Small skinned fibres of skeletal muscle which were perfused with 10 mM caffeine yielded results similar to those obtained in skinned cardiac cells. It was concluded that the mechanism of action of free Mg2+ was similar in both preparations, but that the SR of skeletal muscle had a higher capacity and rate of binding for Ca2+ than the cardiac SR. 4. With a strong buffering of the free [Ca2+] with 4-0 mM total EGTA, a smaller tonic tension was developed for a given pCa in the presence of a higher free [Mg2+]. This result was nearly identical in skinned cells from cardiac and skeletal muscle tissue. 5. A decrease of the [MgATP2-] produced a tension in the skinned cardiac cells that were perfused in Ca2+ free media. The maximum tension was observed for [MgATP2-] 10(-5-50)M as in skinned fibres of skeletal muscle. A further decrease of [MgATP2-] resulted in a decrease of tension.


Pattern and flicker detection analysed by subthreshold summation. 1. We confirm Keesey's (1972) observation that, when a flickering line is viewed, there are distinct thresholds for detecting flicker (or movement) and for detecting a well localized line (pattern detection). Our measurements of the temporal sensitivity of these two mechanisms are similar to Keesey's. 2. The flicker and pattern detection mechanism have been analysed using subthreshold summation, i.e. by observing the effect of subthreshold flickering stimuli (lines and gratings) on the contrast threshold for a flickering test line. 3. The pattern detector shows linear spatial summation of contrast while the flicker detector is non-linear in this respect. 4. The receptive field of the (most sensitive) flicker detector is about two to four times broader than that of the pattern detector. 5. The flicker detector has relatively weak surround inhibition and so, unlike the pattern detector, it is sensitive to a uniform flickering field. 6. The spatial arrangement of the pattern detector is the same at all temporal frequencies (including steady presentation); for flicker detection, the width of the receptive field increases with temporal frequency and the strength of lateral inhibition decreases at high frequencies. 7. Flicker detectors of various widths were demonstrated by using different test stimuli (for 12 Hz modulation); surround ingibition was relatively weak for the broadest detector. 8. There is a delay of surround inhibition of about 3 ms for both flicker and pattern detection. 9. By using a broad test stimulus modulated at a high frequency, a detector can be found with no significant surround inhibition. At threshold, this stimulus produces a sensation of flicker without the appearance of lateral motion observed for finer test lines at lower frequencies. 10. The characteristics of pattern and flicker (movement) detection are compared to electrophysiological studies on X (sustained) and Y (transient) neurones respectively, and correlations are described for studies of temporal frequency response, non-linearity, width of receptive field, strength of the inhibitory surround and motion sensitivity.


Effects of ionic concentration on sodium permeability properties of myelinated nerve fibres of Xenopus laevis. 1. The nodal currents of single myelinated nerve fibres were recorded under potential clamp conditions, and the effect of [Ca], [Na] and [K] in the external solution on some of the Na permeability properties were analysed. 2. [Ca], [Na] and [K] all affected the position of the steady-state Na inactivation (h) curve on the potential axis. The curve was displaced in positive direction by high ionic concentration. 3. The shift associated to different [Ca] was largest in low [Na] and [K]. Similarly the shift associated to different [Na] and [K] was largest in low [Ca]. 4. The maximum peak sodium permeability (max. peak - PNa) was affected by the [Ca], [Na] and [K]. It was greater in (i) low [Ca], (ii) high ([Na] + [K]) and (iii) high [Na]:[K] ratio. 5. The effect of [Ca] on peak - Na was mainly a consequence of a change in PNa (which is the value of PNa if activation were complete, m = 1, and inactivation fully removed, h = 1).


Atrial receptors and heart rate: the efferent pathway. 1. Stimulation of left atrial receptors by distension of the junctions between the pulmonary veins and the left atrium is known to cause a reflex increase in heart rate. It was suggested that the efferent path of this reflex was solely in the sympathetic nerves to the heart but more recently the existence of a vagal efferent component has been postulated by Albrook, Bennion & Ledsome (1972). 3. The junctions between the pulmonary veins and the levt atrium were distended before and after the administration of I.C.I. 66082 and bretylium tosylate. The response of an increase in heart rate was significantly decreased after the administration of I.C.I. 66082 (5 mg/kg) and abolished after the administration of bretylium tosylate (10 mg/kg). 3. It is concluded that the efferent pathway of the reflex is solely in the sympathetic nerves to the heart.


Transport of deutherium oxide across isolated rat small intestine. 1. Transport of deuterium oxide from a luminal perfusate containing 1% D2O was studied in Fisher & Gardners (1974) isolated preparation of perfused rat small intestine. 2. The kinetics of appearance of D2O in the intestinal secretion at the serosal surface fitted well to a single exponential function. 3. The steady-state concentration of D2O in this secretion was not significantly different from the concentration in the luminal perfusate. 4. The total tissue water contained D2O at a concentration, on average, 5% lower than that in the luminal perfusate. 5. There is no evidence to suggest discrimination in transport across the intestinal mucosa between H2O and D2O. 6. The kinetics of wash-in of D2O to intestinal secretion show that the ratio of flux out of the lumen to reflux back to the lumen is 1-38;1.


Prostaglandins, endotoxin and lipid A on body temperature in rats. 1. In unanaesthetized restrained rats kept at an ambient temperature of 21-23degrees C, rectal temperature was continuously monitored and the temperature effects of injections of prostaglandins, endotoxin from Salmonella abortus equi, lipid A, and antipyretics were examined. 2. Fever occurred when prostaglandin E1, E2, F1alpha or F2alpha (PGE1, PGE2, PGF1alpha, PGF2alpha) was injected into the cerebral ventricles in doses of 200 ng and 2 mug. PGE2 was the most potent prostaglandin followed in descending order by PGE1, PGF2alpha, and PGF1alpha. The fever produced by 2 mug of PGE1 and PGE2 was short and followed by a fall in temperature to below the pre-injection level. 3. I.V. injections of endotoxin and lipid A in doses of 3 or 10 mug usually caused a long lasting fall in temperature, but when injected into the cerebral ventricles in doses of 400 ng or 1 mug, they produced long lasting fevers. 4. Injected I.V. or I.P., indomethacin and paracetamol had a hypothermic action of their own. Indomethacin was more potent than paracetamol and both were more potent than injected I.P. 5. I.V. and I.P. injections of indomethacin and paracetamol  did not reverse the hypothermia in response to I.V. endotoxin or lipid A, but the fever responses to their injection into the cerebral ventricles were prevented and abolished by the antipyretics. 6. It is concluded that in rats endotoxin and lipid A, or the endogenous pyrogens produced by them, do not readily pass through the blood-brain barrier into the brain tissue. If they do reach brain tissue, as when injected into the cerebral ventricles, they stimulate synthesis and release of prostaglandin in rats as they do in other species, and thereby produce fever. The hypothermia in response to I.V. endotoxin or lipid A, on the other hand, is thought to be independent of prostaglandin synthesis and to result from a direct toxic action on the skin vessels.


The mode of activation of pyramidal tract cells by intracortical stimuli. 1. Direct and indirect effects of intracortical stimulattion on pyramidal tract cells were compared in the monkey and in the cat under barbiturate or chloralose anaesthesia. The hind-limb motor areas were explored, that in the monkey only within the convex part of the precentral gyrus. The intracortical stimuli were applied in the nearest vicinity of pyramidal tract cells, where antidromic spike potentials of single cells were recorded. 2. Average records of descending volleys in corticospinal tract fibres were taken from the surface of the lateral funiculus or from its dissected fascicles. The sensitivity of the recording was sufficient to detect responses in single fibres. 3. The latencies of the earliest descending volleys evoked by weak intracortical stimuli were compared with the latencies of the antidromic spike potentials of pyramidal tract cells evoked by stimulation of the lateral funiculus at a low lumbar level (same conduction distance). Only in about one third of cases these latencies were similar and compatible with a direct activation of pyramidal tract cells. In the remaining cases they indicated mono- or polysynaptic activation of pyramidal tract cells. 4. Latencies of the later components of the descending volleys indicated that they were due to indirect activation of pyramidal tract cells in practically all cases. 5. The components of the descending volleys attributable to the indirect activation of pyramidal tract cells were greatly increased when repetitive intracortical stimuli were applied instead of single ones. 6. The investigation leads to the conclusion that a weak intracortical stimulation is relatively ineffective in a direct excitation of pyramidal tract cells and that the effects of such a stimulation are mainly indirect, especially when repetitive stimuli are used.


Projections of pyramidal tract cells to alpha-motoneurones innervating hind-limb muscles in the monkey. 1. We have investigated the spatial organization of monosynaptic corticospinal projections to hind-limb motoneurones, using near threshold stimulation of the surface of the precentral gyrus to activate pyramidal tract (PT) cells and intracellular recording from motoneurones to detect the resulting e.p.s.p.s. 2. Monosynaptic e.p.s.p.s. of cortical origin were seen in all motoneurone species investigated, those of distal as well as of proximal hind-limb muscles. The proportion of motoneurones in which the e.s.p.s. were evoked and the amplitudes of the latter indicated a more extensive cortical projection to motor nuclei for distal than for proximal muscles, as previously found for forelimb motoneurones. 3. Cortical areas from which monosynaptic e.p.s.p.s. were evoked in individual motoneurones were remarkably large, most often between 3 and 7 mm2. Several motoneurones appeared to have two or three separate areas within the hind-limb division of the motor cortex. 4. Areas of location of pyramidal tract cells projecting to various motoneurones innervating one muscle were usually not identical. They overlapped often only partially or did not overlap at all. 5. Areas of location of pyramidal tract cells projecting to motor nuclei for different muscles often showed an extensive overlap. When it occurred, various motoneurones of a given motor nucleus had common cortical projection areas with motoneurones of other motor nuclei, either to synergistic or to antagonistic muscles. Our results give further evidence for overlapping of areas of cortical projections to motoneurones and speak against a mosaic-like organization of pyramidal tract cells projecting to different motor nuclei. 6. The rise times of cortically evoked e.p.s.p.s. indicate that the corticospinal tract fibres terminate on motoneurones at approximately similar distances from the soma as group Ia afferents. The small amplitudes of the majority of e.p.s.p.s. evoked by near threshold cortical stimulation therefore suggest that unitary e.p.s.p.s of cortical origin are small and that the density of pyramidal tract cells projecting to individual motoneurones is usually low, even in the centrum of projection areas. 7. Effects of intracortical stimulation depended on the stimulus strength. With currents of 2-3 muA, e.p.s.p.s were usually evoked in one motoneurone species or in close synergists. With currents of 5-10 muA, largest e.p.s.p.s a number of other motoneurones. Latencies of descending volleys in the lumbar corticospinal tract indicated that intracortical stimuli activated pyramidal tract cells indirectly; the effects of these stimuli could thus not be used to indicate the location of pyramidal tract cells responsible for them.


The effect of ouabain on ion transport across isolated sheep rumen epithelium. 1. The net flux of Na from the lumen to the blood side of isolated sheep rumen epithelium was reduced to zero in the third 30 min period after treatment with ouabain. 2. The net flux of K from blood to lumen side of the epithelium was reduced from 0-34 to 0-13 mumole/cm2. hr in the third 30 min period after ouabain treatment. 3. The net flux of Cl from lumen to blood side of the epithelium was reduced from 1-4 to 0-72 mumole/cm2. hr in the third 30 min period after ouabain treatment. 4. The results support the existence of a Cl pump independent of Na transport and also a K pump in sheep rumen epithelium.


Characterization of acetylcholine receptors in the Schwann cell membrane of the squid nerve fibre. 1. The effects of alpha-bungarotoxin, nicotine and muscarine on the Schwann cell membrane potential have been studied in the giant nerve fibre of the squid. The external application of alpha-bungarotoxin (10(-6), 10(-8), 10(-9) M) irreversibly blocks the long-lasting Schwann cell hyperpolarizations following the conduction of nerve impulse trains by the axon. It also blocks the Schwann cell hyperpolarizing response to the external application of carbamylcholine (10(-6)M) to the resting nerve fibre. 2. Externally applied D-tubocurarine (10(-5)M) protects against the irreversible action of alpha-bungarotoxin (10(-9)M) on the Schwann cell. Within 10 min of reimmersion in toxin-free sea water there is complete recovery of the Schwann cell hyperpolarizing response to carbamylcholine (10(-6)M) which had been initially abolished. 3. Nicotine (10(-6)M) induces a prolonged hyperpolarization of the Schwann cells in the resting nerve fibre, wheras at the same concentration, muscarine has no appreciable effect on the Schwann cell membrane potential. 4. None of these drugs, at the concnetrations utilized in the present study, had any appreciable effect on the resting and action potentials of the axon. 5. These findings show the presence of acetylcholine receptors of the nicotinic type in the Schwann cell membrane, and give further support to the hypothesis on the role of the acetylcholine system in the genesis of the long-lasting Schwann cell hyperpolarizations caused by the conduction of nerve impulse trains by the axon.


Effects of stimulating the acetylcholine receptor on the current-voltage relationships of the smooth muscle membrane studied by voltage clamp of potential recorded by micro-electrode. 1. A double sucrose-gap voltage-clamp technique is described for use on smooth muscle strips longer than about 2 mm. It involves intracellular recording by microelectrode of the membrane potential of a narrow region of the strip ("node") sandwiched between two streams of deionized sucrose solution. Current was passed into the node across one or both sucrose streams. 2. Preliminary experiments in which potential was recorded intracellularly at two points during polarization of a "short cable" preparation, formed by folding over a strip of smooth muscle, suggested that a node width of less than 0-15 mm was needed to achieve uniform potential during inward current flow. However, when node width between sucrose-gaps was reduced to 0-5 mm, spontaneous electrical activity was lost, and below 0-5 mm spike threshold was raised and the regenerative spike became graded. The currents flowing during the application of rectangular voltage-clamp command potentials were described. 3. Using taenia smooth muscle it was shown by recording with a second, independent micro-electrode that potential was not uniform for up to 200 ms or more following a step change in potential under voltage-clamp in nodes 0-4-0-5 mm wide where current was passed across both sucrose gaps. However, reasonably uniform nodal potentials were obtained using ramps with relatively slow rates of rise (25 mV/s). 4. Using such slow ramp commands under voltage clamp, the effects of carbachol on the current-voltage relationship of longitudinal muscle of ileum and taenia were studied in hypertonic solution. 5. In the presence of carbachol (10(-6) to 10(-5) g/ml.) additional inward current flowed across the membrane (in some experiments an equilibrium potential was observed at which this current reversed direction). The magnitude of this additional current was linearly related to potential at potentials negative to the resting potential. At potentials positive to the resting membrane potential, this additional current increased with depolarization over the range -40 to -10 mV; in ileum the effect of this additional inward current on the current-voltage relationship was to produce a region of net inward current where before, in the absence of carbachol, a net outward current existed. In taenia the additional inward current flowing in the presence of carbachol was too small to produce a region of net inward current; thus carbachol produced regenerative slow oscillations of potential (slow waves) in ileum but not in taenia. 6. These results support a previous suggestion that activation of the acetylcholine receptor of ileal smooth muscle produces an additional inward current in the membrane which increases with depolarization and is responsible for the regenerative slow waves seen when muscarinic stimulants are applied. A similar effect apparently operates in taenia but the additional inward current is too small to produce regenerative slow waves.


The mechanism of acute renal ischaemia caused by adrenalectomy in the rat. 1. The acute reduction of renal blood flow following adrenalectomy in the rat, which had previously been shown to be associated with sequestration of blood volume in the splanchnic area, was further investigated. An attempt was made to define the role of the renal sympathetic nerves in causing the blood flow change. 2. The systemic and renal intra-arterial administration of phenoxybenzamine, isoprenaline and propranolol and denervation of the renal pedicle failed to re-establish normal renal function. 3. Infusion of P113 (sarcosyl1 alanine8), an angiotensin blocker, failed to improve renal function. 4. In contrast, volume replacement with high-molecular weight PVP caused a prompt increase of RPF and GFR without altering arterial pressure and central venous pressure. 5. Angiographic studies demonstrated that the calibre of the aorta of adrenalectomized rats was significantly smaller than that of the sham operated and increased after the administration of this plasma volume expander. 6. It was concluded that after adrenalectomy the major arteries readjusted their calibre to the reduced volume of blood in the arterial tree with maintenance of a constant pressure/volume relationship. Their contracted state in the case of the kidney then led to flow reduction.


Actions of gamma-aminobutyric acid on sympathetic ganglion cells. 1. Responses of single ganglion cells in the isolated rat superior cervical ganglion to gamma-aminobutyric acid (GABA) applied via the bathing medium were recorded using intracellular micro-electrodes. 2. GABA produced a large fall in cell input resistance, frequently to immeasurable levels. In thirteen cells showing a modest response to 100 muM GABA, input resistance fell from 50-5 +/-9-5 to 15.9 +/- 3-2 Momega (means +/- S.E. of mean). After correction for resistance leaks introduced by the impaling electrode, the resting membrane resistance Rm and the resistance of the GABA-shunt Rg in these cells were calculated to be 79-3 +/- 16-6 and 35-0 +/- 9-5 Momega respectively. 3. Cells with recorded resting membrane potentials greater than -42 mV were depolarized by GABA; at resting potential less than -42 mV they were hyperpolarized...


Aerobic and anaerobic metabolism in smooth muscle cells of taenia coli in relation to active ion transport. 1. The O2 consumption and lactic acid production of the guinea-pig's taenia coli have been studied in relation to the active Na-K transport, in order to estimate the ratio: active Na extrusion/active K uptake/ATP hydrolysis. 2. By applying different procedures of partial metabolic ingibition, it was found that a reactivation of the active Na-K transport in K-depleted tissues could occur in an anaerobic medium, provided glucose was present and in an aerobic medium free of added metabolizable substrate. The active Na-K transport was rapidly blocked in an anaerobic-substrate free medium. 3. Readmission of K to K-depleted tissues under aerobic conditions stimulates both O2 consumption and lactic acid production. While the O2 consumption creeps up slowly and requires 50 min to reach control values, the aerobic lactic acid production increases to a maximum within 10 min and decreases again during the next 50 min to its steady-state value. 4. A reactivation of the Na-pump in K-depleted cells in a N2-glucose medium causes an immediate increase of the lactic acid production, which decreases to its control value after 60 min. The maximal increase in anaerobic lactic acid production during reactivation of the Na-K pump is a function of [K]O. The system can be cescribed with first order kinetics having a Vmax = 0-72 mumole.g-1 f. wt. min-1 and a Km = 1-1 mM. 5. By varying the glucose concentration of [K]O during reactivation of the Na-K pump, different Na-K pumping rates can be obtained. The ratios net Na extrusion/ATP or net K accumulation/ATP amount to -1-32 +/- 0-19 (36) and 1-02 +/- 0-11 (36), in the experiments with different glucose concentrations. Taking into account the interference by net passive fluxes, one can estimate a ratio:active Na transport/active K transport/ATP, of 1-7/0-8/1. This ratio is not very different from the values observed in other tissues.


Effect of intracellular injection of calcium and strontium on cell communication in heart. 1. The influence of Ca and Sr on the electrical coupling of canine Purkinje cells was investigated by injecting the ions electrophoretically into the cytoplasm. 2. It was found that the intracellular injection produced electrical uncoupling which was spontaneously reversed. 3. No change in resting potential of the cell adjacent to the injection site was found except in those fibres not completely healed. 4. The input resistance of the injected cell increased concomitantly with the establishment of the electrical uncoupling. 5. Caffeine (6mM), added to the extracellular fluid, reduced the rate of spontaneous recoupling. Reduction of temperature of the Tyrode solution had the same effect. 6. The abolition of cell communication produced by Ca injection seems to indicate that the ion plays an important role in the control of junctional conductance in heart fibres.


The effectiveness of bicuculline as an antagonist of GABA and visually evoked inhibition in the cat's striate cortex. 1. The iontophoretic application of the alkaloid bicuculline to neurones in area 17 of the cat's visual cortex effectively antagonized the inhibitory action of iontophoretically applied GABA in fifty-four out of sixty-two neurones examined. It had little or no effect on the inhibitory action of iontophoretically applied glycine. 2. At the stage that the iontophoretic application of bicuculline blocked the inhibitory action of GABA it also reduced or blocked visually evoked inhibitory influences acting on forty-three of the fifty-four cells. This effect on visually evoked inhibition was not reproduced by simply raising the neural spontaneous activity with iontophoretically applied glutamate. 3. For those seven neurones where the iontophoresis of bicuculline failed to block the inhibitory action of iontophoretically applied GABA it also failed to produce any change in visually evoked inhibition. 4. In all cases where a visually evoked inhibition of a cells resting discharge was reduced by the iontophoretic application of bicuculline, the inhibitory response was replaced by an excitatory response. The application of bicuculline also revealed excitatory responses to certain of the visual stimuli that previously appeared to exert neither inhibitory nor excitatory effects on a cell, and often where cells normally exhibited small excitatory responses it produced large increases in the magnitude of the evoked response. 5. These results indicate that the normal responses of the neurones examined in the present work, to the particular visual stimuli used, reflect an interaction between simultaneously evoked excitatory and inhibitory inputs. It is suggested that the iontophoretic application of bicuculline by blocking or reducing the inhibitory input moves the balance between the inputs in favour of the excitatory input. 6. The present results support the view that GABA is an inhibitory transmitter in the visual cortex.


The contribution of inhibitory mechanisms to the receptive field properties of neurones in the striate cortex of the cat. 1. The iontophoretic application of the GABA antagonist bicuculline to simple and complex cells in the striate cortex of the cat produced extensive modifications of receptive field properties. These modifications appear to relate to a block or reduction of GABA-mediated intracortical inhibitory influences acting on the cells examined. 2. For simple cells the effects of bicuculline on receptive field properties involved a loss of the subdivision of the receptive field into antagonistic "on" and "off" regions, a reduction in orientation specificity and a reduction or elimination of directional specificity. 3. The effect on the "on" and "off" subdivisions of the simple cell receptive field was such that all stationary flashing stimuli, whether covering the whole receptive field, or located within the receptive field over a previously determined "on" or "off" region, resulted in an "on and off" response. 4. The orientation specificity of complex cells was reduced during the application of bicuculline such that in many cases the original specificity of the cell was virtually lost with the response to the orientation at 90 degrees to the optimal being of similar magnitude to the optimal. The directional specificity of complex cells was generally less affected than that of simple cells. Often when large changes in orientation specificity were observed the directional specificity was relatively unaffected. 5. For some cells apparently showing to all visual stimuli only inhibitory responses, the application of bicuculline resulted in the appearance of excitatory responses. 6. In all cases receptive field properties reverted to the original state after termination of the bicuculline application. It was not generally possible to duplicate the effects of bicuculline by raising neuronal excitability with iontophoretically applied glutamate. 7. On the basis of these results it is suggested that the normal subdivision of the simple cell receptive field into separate "on" and "off" regions and its directional specificity are dependent on intracortical inhibitory processes that are blocked by bicuculline. The orientational tuning of simple cells conversely appears to be largely determined by the excitatory input but normally enhanced by lateral type inhibitory processes acting in the orientation domain. 8. It also appears that the excitatory input to some complex cells is not orientation specific. This suggests that for these cells it is extremely unlikely that they receive an orientation specific excitatory input from simple cells.


The independence of channels in human vision selective for direction of movement. 1. Human visual selectivity for direction of movement was determined using a subthreshold summation technique. 2. The threshold contrast for detecting a drifting sinusoidal grating was found to be independent of the contrast of an added subthreshold grating which moved in the opposite direction. 3. The detection threshold for a counterphase flickering grating is twice that for a moving grating, suggesting that the visual system analyses a counterphase grating as the sum of two half-contrast gratings which move in opposite directions. 4. Threshold for a counterphase grating may be linearly reduced by the addition of subthreshold background gratings drifting in either direction. Additivity between counterphase grating and moving background is complete. 5. After adaptation to a drifting grating, the behaviour of counterphase detection threshold as a function of the contrast of a moving subthreshold background depends upon the direction of background movement. When the background moves in a direction opposite that of the adaptation stimulus, complete linear additivity results. When the background moves in the same direction as the adapting grating, counterphase threshold is constant for low background contrasts, but drops linearly for higher background contrasts. 6. The results support the hypothesis that directionally selective channels in human vision are independent contrast detectors. Counterphase gratings are detected by one or the other of these direction-specific mechanisms, whichever is momentarily the more sensitive.