Neuronal activity of the cerebral cortex in cats with conditioned inhibition

Unit activity of the somatosensory cortex was studied in chronic experiments on cats during alimentary instrumental conditioned reflex performance and elaboration of conditioned inhibition (CI). First presentations of the CI signal at the beginning of CI formation caused, due to orienting reaction to a new stimulus, a levelling of the response of the neurones to the positive conditioned signal included into the CI complex. At the stage of consolidated CI, this depression proceeded gradually during the development of conditioned inhibition caused by consecutive presentations of the nonreinforced CI combination. Two groups of neurones were involved in the process of the CI performance: one of them being the same which was activated also in response to positive stimulation during performance of the conditioned response, and the second one being areactive to the positive conditioned stimulus but reducing the frequency of the background activity.     

Neuronal responses in the limbic cortex of awake cats during defensive conditioning

Spike activity was investigated in limbic cortex neurons during defensive conditioning to acoustic stimulation in chronic experiments on cats. A relationship was found between the numbers of neurons responding, their contribution to formation of a temporal connection, and the duration of the acoustic stimulus. Phasic responses of 50–500 msec duration with latencies of 15–50 msec were observed for the most part. Intensive spike response with a minimum latency of 15 msec and a duration of between 200 msec and 2.5 sec evolved in most cells (95.1% in field 24 and 83% in field 32) in response to electrical stimulation. Response to acoustic stimulation rose during defensive conditioning in 33.3% cells and declined and finally disappeared in 13.3%, but response at the site where reinforcement was abolished was reproduced in all these cells. It was thus found that the numbers of limbic cortex neurons responding to sound not only fails to increase but actually decreases after training. The limbic cortex is thought to play its most active part in conditioning response to a recognized signal during the period preceding the awaited painful reinforcement.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 5, pp. 660–669, September–October, 1986.     

Neuronal interaction in the auditory cortex of alert cats

Spontaneous activity of neighboring auditory cortical neurons was derived by glass microelectrodes in chronic experiments on unanesthetized, unimmobilized cats, and the spike trains were subsequently analyzed by computer. Altogether 20 pairs of neurons were tested. The commonest type of interaction (50%) was found to be a common excitatory source, conjectured to be from specific auditory afferents. Interaction of the "common inhibitory source" (5%) and also complex forms of interaction were found. Interaction was absent in only 10% of cases. No direct inhibitory influence of neighboring neurons on one another was observed. The possible causes of absence of a direct inhibitory action are discussed. The most likely cause is absence of marked spontaneous activity in inhibitory auditory cortical neurons.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 2, pp. 161–167, March–April, 1984.     

Neuronal responses of a chronically isolated slab of auditory cortex to intracortical stimulation during paroxysmal electrical activity in cats

Responses of 155 neurons 3 weeks after neuronal isolation of a slab of auditory cortex (area AI) to single intracortical stimulating pulses at the level of layer IV were studied in unanesthetized, curarized cats during paroxysmal electrical activity evoked by series of high-frequency (10–20 Hz) electrical stimulation by a current 2–5 times above threshold for the direct cortical response. In response to such stimulation a discharge of paroxysmal electrical activity, lasting from a few seconds to tens of seconds, appeared in the slab. As a rule it consisted of two phases — tonic and clonic. This indicates that cortical neurons can form both phases of paroxysmal cortical activity. Depending on behavior of the neurons during paroxysmal electrical activity and preservation of their ability to respond to intracortical stimulation at this time, all cells tested in the isolated slab were divided into four groups. Their distribution layer by layer and by duration of latent periods was studied. Two-thirds of the neurons tested were shown to generate spike activity during paroxysmal discharges whereas the rest exhibited no such activity. A special role of neurons in layer II in generation of paroxysmal activity in the isolated slab was noted. The view is expressed that at each moment functional neuronal circuits, independent of each other, exist in the slab and also, evidently in the intact cortex, which can interact with one another when conditions change.I. I. Mechnikov Odessa State University. Translated from Neirofiziologiya, Vol. 16, No. 1, pp. 3–11, January–February, 1984.     

Neuronal interaction in the cat cerebellar cortex: A cross correlation analysis

Neuronal interaction in the cat cerebellum was investigated by cross correlation analysis techniques. Excitatory connections of varying effectiveness were found between neurons of 13 out of 90 pairs investigated (or 14%). Inhibitory interaction was observed in 38 pairs, or 42%. Neurons of 26 pairs (40%) had shared inputs. Effectiveness of connections between cerebellar cortex neurons was demonstrated by changing stimulus parameters. Findings obtained agree with existing data on the functional organization of the cerebellar cortex. Possible reasons for the large numbers of inhibitory connections discovered are discussed.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow, Institute of Experimental Biology, Polish Academy of Sciences, Warsaw. Translated from Neirofiziologiya, Vol. 19, No. 5, pp. 672–678, September–October, 1987.     

Activity of cat cerebellar neurons in penicillin epilepsy and amphetamine treatment.

The discharge pattern of cerebellar Purkinje cells and fastigial neurons was studied after acute amphetamine treatment in immobilized cats, as well as during generalized penicillin-induced epilepsy. There was a marked reversible decrease in spontaneous firing rate of Purkinje cells and an increase in spontaneous firing rate of fastigial neurons after acute d-1 amphetamine administration (5 mg/kg, s.c.). The discharge pattern of Purkinje cells showed tendency towards inhibition, while the fastigial neurons showed less clear tendency towards disinhibition in the course of epilepsy induced by parenteral administration of penicillin (400.000-500.000 I.U./kg, i.m.). Moreover, acute amphetamine treatment (5 mg/kg, s.c.) performed after the development of penicillin-induced epileptic episodes elicited a prominent suppression of Purkinje cell discharges associated with a parallel increase in discharges of fastigial neurons. These results suggest that the changes in discharge rate of cerebellar corticonuclear neurons induced by amphetamine contribute to suppression of seizural activity in the feline model of generalized epilepsy.     

Neuronal septal activity during hippocampal seizure discharges generation in acute model of epilepsy

The activity of the neurones of the medial septal region (MS) and the hippocampal EEG in control and during the appearance of seizure discharges provoked by electrical stimulation of the perforant path were investigated in the awake rabbit. During afterdischarge generation in the hippocampus the dense neuronal bursts separated by periods of inhibition were recorded in the MS. In one group of neurons the bursts of spikes coincided with the discharges in the hippocampus, in other group-occured during inhibitory periods. When the afterdischarge stopped, in the septal neurons with theta activity the disruption of theta pattern was recorded, which have been correlated with the occurrence of low amplitude high frequency (20-25 Hz) waves in the hippocampal EEG. As a rule, the neuronal activivity of the MS recovered much quickly than EEG of the hippocampus; in some cases the increasing of the theta regularity was observed. The definite accordance of the electrical activity of the hippocampus and MS during seizure discharges suggests that the septohippocampal system operate as integral nervous circuit in these conditions. Diverse in the temporal interrelations between the discharges of MS neurones and ictal discharges in the hippocampus in the different cells possible indicate that various groups of the septal nervous elements have different participation in the seizure development. Appearance of the high frequency bursts in the MS is a possible "precursor" of the seizure onsets.     

Neuronal connections of ocular dominance columns in the cortex of monocularly deprived cats

We have investigated the developmental changes of intrahemispheric neuronal connections of the areas 17 & 18 ocular dominance columns in monocularly deprived cats. Single cortical columns were microiontophoretically injected with horseradish peroxidase and 3D reconstruction of retrogradely labelled cells' region was done. Ocular dominance of injected columns and their coordinates in the visual field map were determined. In area 17 it was shown that for non-deprived eye the connections of columns that are driven via the crossed pathways were longer than connections of columns driven via uncrossed ones, and in both cases they were longer than connections in intact cats. The connections of deprived eye columns are significantly reduced. We have observed some changes in the spatial organization of long-range connections in area 17 for columns driven by the non-deprived eye (more rounded shape of regions of labeled cells, non-uniform distribution of cells within it). Maximal length of such connections did not exceed the length of connections in strabismic cats. We speculate that the length of cell axons providing for the horizontal connections of cortical columns has some intrinsic limit that does not depend on visual stimulation during the critical period of development.     

Neuronal activity in the prefrontal cortex in rats with various typological features during emotional affect

Unit activity in the right and left prefrontal cortex was recorded in male Wistar rats after testing by the emotional resonance technique. Rats were divided in two groups by their reaction to the suffering cry of a partner. Rats from the group A ("altruists") escaped partner's crying, and those from the group E ("egoists") did not. Activity of neurons was analyzed in hungry rats, after feeding, during intracranial emotionally positive and negative stimulation, and during crying of the rat partner. Some differences in neural activity between A and E groups were revealed. In the hungry state the rate of neuronal discharges was higher in the A group. In both groups of animals the positive emotional stimulation was accompanied by more intensive neuronal reaction that the negative stimulation, but in the E group increase in the rate of neuronal discharges in both hemispheres was significantly more pronounced. Negative stimulation produced in both groups a significantly greater activation in the left hemisphere than in the right one while during the positive stimulation the neural activity was more intensive in the left hemisphere. The neuronal reaction to partner's crying was significantly higher in the A group in both hemispheres, while the neuronal activity in E group did not significantly change.     

Dynamics of single unit activity in the association cortex of waking cats during defensive conditioning

Responses of neurons in association area 5 during defensive conditioning to acoustic stimulation were studied in chronic experiments on cats. As a rule the neurons responded by excitation to presentation of conditioned and unconditioned stimuli. During the conditioned reflex unit responses usually appeared in the first 50 msec after the beginning of acoustic stimulation, i.e., they were connected with the action of the conditioned stimulus and not with manifestations of conditioned-reflex motion. The most significant changes in responses of cortical association units were observed in the initial period of conditioning. During stabilization of the conditioned reflex, responses of some neurons became stabilized, whereas in other neurons the spontaneous activity and intensity of responses increased, and in a third group the response to one of the stimuli disappeared. This last result indicates a switch during conditioning from polysensory unit responses to monosensory specialized responses. Extinctive inhibition was found to consist of a gradual decrease in the level of the spike discharge and its approximation to spontaneous activity, i.e., to be passive in character.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 6, pp. 563–572, November–December, 1978.