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.     

Effect of pentobarbital on neuronal inhibitory response evoked in an isolated slab of cat auditory cortex by intracortical stimulation

Neuronal responses of an acutely isolated slab of auditory cortex (area AI) to intracortical electrical stimulation were studied intracellularly in cats anesthetized with pentobarbital. It was found that 77% of responses were primary IPSPs, and allowing for secondary inhibitory responses, an inhibitory response was observed in 92% of neurons. All types of neuronal responses in the slab were short-latency. The maximal response latency did not exceed 5 msec. Neurons responding to stimulation by IPSPs were found at all depths in the slab, with a maximum in layers II–III. Nearly all primary IPSPswere mono- and disynaptic. Pentobarbital increased the duration of individual neuronal inhibitory responses in the isolated slab of auditory cortex without affecting maximal duration of the IPSP. The mechanisms of the effect of pentobarbital on the amplitude and duration of IPSPs are discussed.I. I. Mechnikov Odessa State University. Translated from Neirofiziologiya, Vol. 16, No. 2, pp. 147–152, March–April, 1984.     

Neuronal response in a strychninized cortical slab isolated from the cat

Intracellular response in neurons and glial cells of an isolated cortical slab to direct electrical stimulation of the slab following surface application of strychnine was investigated during experiments on immobilized unanesthetized cats. Strychnine induced single epileptiform discharges and after-discharges in the slab and in the neurons it contained in the form of large-scale paroxysmal depolarization shifts (PDS) in membrane potential (MP). Spontaneous summated epileptiform discharges and neuronal activity in the units examined were not very synchronized. Electrical stimulation induced generalized paroxysmal activity in the isolated slab. Neuronal PDS were accompanied by refractory periods, onset of which did not depend on MP level. Strychnine increased the number of neurons manifesting background activity in which action potentials were generated by rhythmic depolarizing MP waves of extrasynaptic origin. Epileptiform response in strychninized cortical isolated slabs to presentation of single stimuli is accompanied by major depolarization shifts in the MP of glial cells. Paroxysmal excitation is thought to be triggered in strychninized isolated cortical slabs by extrasynaptic factors and closely linked to altered concentration of extracellular potassium.I. I. Mechnikov University, Odessa. Translated from Neirofiziologiya, Vol. 22, No. 1, pp. 23–29, January–February, 1990.     

Primary neuronal inhibitory responses of a chronically isolated slab of auditory cortex to intracortical stimulation in cats

Responses of 579 neurons in a slab of cerebral cortex (3 weeks after its isolation) to intracortical stimulation, with a distance of 0.5, 1.0, and 2.0 mm between recording and stimulating electrodes, were tested intercellularly and histological changes in a similar slab were studied in experiments on cats. Primary IPSPs were shown to develop in the chronically isolated slab in a much larger number of neurons than in the acutely isolated slab. Latent periods of IPSPs in all series of experiments did not exceed 10 msec, and most IPSPs were mono- and disynaptic. The amplitude and duration of the IPSPs were similar to those observed in the acutely isolated slab and intact auditory cortex in cats. It is concluded that local intracortical neuronal chains along which impulses evoking an inhibitory effect in the terminal neuron of the chain are transmitted are of relatively short length. Such chains may participate in local processing of incoming information. Analysis of the distribution of neurons responding by primary IPSPs by duration of their latent periods and depth in the slab in each series of experiments revealed a spatial and temporal mosaic of inhibitory responses in the chronically isolated slab of auditory cortex and showed that this mosaic is due to intracortical mechanisms.I. I. Mechnikov Odessa State University. Translated from Neirofiziologiya, Vol. 16, No. 2, pp. 152–161, March–April 1984.     

Neuronal responses in an isolated slab of the cat auditory cortex to intracortical stimulation

Neuronal responses in an isolated slab (area AI) to intracortical pulsed electrical stimulation at the level of layer IV were investigated extracellularly in acute experiments on cats immobilized with D-tubocurarine. Responding neurons were found in all layers of the slab. The character of their distribution by depth in the slab depended on the distance between recording and stimulating electrodes. The latent period of responses of different neurons ranged from 0.8 to 25 msec. With interelectrode distances of 0.5–2 mm most neurons responded mono- and disynaptically. However, responses of many neurons had a latent period of over 4 msec, i.e., they were polysynaptic. This indicates the complex character of interneuronal interactions, even in a limited area of the cortex. After intracortical stimulation no after-discharges with a latent period of over 40 msec could be recorded in the isolated slab of auditory cortex.I. I. Mechnikov Odessa State University. Translated from Neirofiziologiya, Vol. 14, No. 1, pp. 85–93, January–February, 1982.     

Neuronal inhibitory responses to intracortical stimulation of an isolated slab of cat auditory cortex

Neuronal responses of an isolated slab of cortex to intracortical stimulation were studied intracellularly. The predominant responses were primary IPSPs. Their latent periods did not exceed 10 msec. Within the volume of cortex studied, neurons inhibited in response to stimulation were most numerous in the upper layers (II, III). Predominance of disynaptic IPSPs is evidence of the important role of cortical interneurons in their genesis. It is concluded from the results that primary IPSPs limit the spread of excitation primarily in the activated area of cortex. Since involvement of neurons of the isolated slab in the inhibition process takes place for only 10 msec after stimulation, neurons giving spike responses to intracortical stimulation with a longer latent period can transmit information into other brain zones. The role of duration of IPSP in the dynamics of interneuronal interaction in the cerebral cortex is discussed.I. I. Mechnikov Odessa State University. Translated from Neirofiziologiya, Vol. 16, No. 1. pp. 42–49, January–February, 1984.     

Protracted depolarizing potentials of neurons in a strychninized cortical slab isolated from the cat

Neuronal response in a cortical slab isolated from the cat during surface application of strychnine was investigated in experiments on immobilized unanesthetized animals by means of intracellular recording techniques. Protracted depolarizing potentials (PDP) were found to occur spontaneously and in response to a single intracortical electrical stimulus in a proportion of the neurons. These potentials could be triggered by transformation of response along the lines of "paroxysmal depolarizing shift" (PDS) — hyperpolarization, with hyperpolarization replaced by depolarizing potentials. A further increase in depolarizing after-potentials resulted in the generation of PDP. These changes were normally accompanied by enhanced summated epileptiform activity in the isolated cortical slab. It is postulated that PDP were triggered by increased calcium conductance at the neuronal membrane during intensification of paroxysmal response in the isolated cortical slab.I. I. Mechnikov University, Odessa. Translated from Neirofiziologiya, Vol. 22, No. 1, pp. 19–23, January–February, 1990.     

Neuronal responses of an isolated slab of cat auditory cortex to intracortical stimulation

Neuronal responses of an isolated slab of auditory cortex (area AI) to intracortical stimulation at the level IV were studied in curarized cats by extracellular recording 3 weeks after isolation. Dispersion of response latencies in the isolated slab was reduced (compared with that observed soon after isolation); the predominant responses were mono- and disynaptic, and the number of discharges consisting of bursts of spikes increased. However, despite simplification of the structural and functional organization of the chronically isolated slab of auditory cortex, the conditions for complex polysynaptic interaction between neurons of all layers were preserved in it, and in each layer the character of such interaction depended on the distance of the neuron from the focus of origin of the excitation. [In the chronically isolated slab of auditory cortex, just as in the acutely isolated slab, late reponses of over 40 msec were absent.]I. I. Mechnikov Odessa State University. Translated from Neirofiziologiya, Vol. 14, No. 5, pp. 462–469, September–October, 1982.     

Spread of excitation in upper layers of the cat auditory cortex with participation of intracortical interneuronal connections

In chronically isolated slabs of the cat auditory cortex with additional transection of lower layers and preservation of the structural integrity of one, two, or three upper layers of cortex just under the pial membrane, impulse responses of slab neurons to stimulation applied at the additionally undercut section were studied. High effectiveness of axodendritic and axospinal excitatory contacts formed by nerve elements of intracortical origin in upper cortical layers was demonstrated. The participation of geniculocortical fibers in spread of excitation in the cortex through synaptic contacts in layer I with dendrites of underlying-layer pyramidal neurons is discussed. The capacity for generation of polysynaptic excitation responses by the neurons indicates preservation of complex interneuronal interactions in the isolated cortex slab preparations with their undercut lower layers.I. I. Mechnikov State University of Odessa, Odessa. Translated from Neirofiziologiya, Vol. 23, No. 1, pp. 80–87, January–February, 1991.     

Neuronal electrical activity in the epileptic focus produced by electrical stimulation in an isolated cortical slab

Characteristics of neuronal activity in an isolated cortical slab were investigated during the onset of seizure spikes induced by frequent and powerful stimulation of the slab during experiments on unanesthetized immobilized cats. A high degree of coordination between the activity of cellular elements was found in the focus of epileptiform activity studied: convulsive shifts in membrane potential exactly corresponding to electrocorticograms of convulsive activity waves were observed in all neurons studied using intracellular techniques. No action potentials occurred in the soma of any of these neurons, moreover. Bursting spike discharges were recorded from neurons of the isolated slab at the same time. Findings from extra- and intracellular recordings of activity in the same neurons showed that action potentials are generated during convulsive activity at certain trigger zones remote from the cell in question without involving the soma, from which convulsive shifts in membrane potentials were recorded simultaneously. Mechanisms possibly underlying the generation of spike activity in neurons of the isolated slab undergoing development of generalized convulsive state are discussed.I. I. Mechnikov State University, Odessa. Translated from Neirofiziologiya, Vol. 20, No. 3, pp. 357–365, May–June, 1988.     

Unit responses in the cat auditory cortex to medial geniculate body stimulation

Responses of 98 auditory cortical neurons to electrical stimulation of the medial geniculate body (MGB) were recorded (45 extracellulary, 53 intracellularly) in experiments on cats immobilized with tubocurarine. Responses of the same neurons to clicks were recorded for comparison. Of the total number of neurons, 75 (76%) responded both to MGB stimulation and to clicks, and 23 (24%) to MGB stimulation only. The latent period of extracellularly recorded action potentials of auditory cortical neurons in response to clicks varied from 7 to 28 msec (late responses were disregarded), and that to MGB stimulation varied from 1.5 to 12.5 msec. For EPSPs these values were 8–13 and 1–4 msec respectively. The latent period of IPSPs arising in response to MGB stimulation varied from 2.2 to 6.5 msec; for 34% of neurons it did not exceed 3 msec. The difference between the latent periods of responses to clicks and to MGB stimulation varied for different neurons from 6 to 21 msec. Responses of 11% of neurons to MGB stimulation, recorded intracellularly, consisted of sub-threshold EPSPs, while responses of 23% of neurons began with an EPSP which was either followed by an action potential and subsequent IPSP or was at once cut off by an IPSP; 66% of neurons responded with primary IPSPs. Neurons responding to MGB stimulation by primary IPSPs are distributed irregularly in the depth of the cortex: there are very few in layers III and IV and many more at a depth of 1.6–2 mm. Conversely, excited neurons are predominant in layer III and IV, and they are few in number at a depth of 1.6–2 mm. It is concluded that the afferent volley reaching the auditory cortex induces excitation of some neurons therein and, at the same time, by the principle of reciprocity, induces inhibition of others. This afferent inhibition takes place with the participation of inhibitory interneurons, and in some cells the inhibition is recurrent. The existence of reciprocal relationships between neurons in different layers of the auditory cortex is postulated.A. A. Bogomolets' Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 1, pp. 23–31, January–February, 1972.     

Neuronal responses of the reticular and anterior ventral thalamic nuclei to stimulation of the thalamic ventrolateral nucleus and motor cortex

Responses of 137 neurons of the rostral pole of the reticular and anterior ventral thalamic nuclei to electrical stimulation of the ventrolateral nucleus and motor cortex were studied in 17 cats immobilized with D-tubocurarine. The number of neurons responding antidromically to stimulation of the ventrolateral nucleus was 10.5% of all cells tested (latent period of response 0.7–3.0 msec), whereas to stimulation of the motor cortex it was 11.0% (latent period of response 0.4–4.0 msec). Neurons with a dividing axon, one branch of which terminated in the thalamic ventrolateral nuclei, the other in the motor cortex, were found. Orthodromic excitation was observed in 78.9% of neurons tested during stimulation of the ventrolateral nucleus and in 52.5% of neurons during stimulation of the motor cortex. Altogether 55.6% of cells responded to stimulation of the ventrolateral nucleus with a discharge of 3 to 20 action potentials with a frequency of 130–350 Hz. Similar discharges in response to stimulation of the motor cortex were observed in 30.5% of neurons tested. An inhibitory response was recorded in only 6.8% of cells. Convergence of influences from the thalamic ventrolateral nucleus and motor cortex was observed in 55.7% of neurons. The corticofugal influence of the motor cortex on responses arising in these cells to testing stimulation of the ventrolateral nucleus could be either inhibitory or facilitatory.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 5, pp. 460–468, September–October, 1978.     

Responses of auditory cortex neurons in unanesthetized cats to best-frequency tones

The characteristics of extra- and intracellular responses of neurons in the AI region were studied in experiments with unanesthetized cats. It was established that auditory cortex neurons with similar best frequencies showed different forms of responses to tones of the corresponding frequency. About 40% of the auditory cortex neurons generated on responses to tone presentation. On — off and off responses were found in 27% of the neurons. Cortical neurons (27%) in which stimulation or inhibition of impulse discharge persisted throughout tone action were assigned to the tonic type group of cells. Approximately 6% of neurons in the AI region did not respond to a tone. During intracellular recording about 85% of the neurons responded to the turning on and/or off of a tone by generating an action potential followed by an IPSI. In 96% of the cortical neurons studied the IPSPs were a constant component of the intracellular responses to a tone. It is concluded that the inhibition of the impulse activity of the given neurons is of primarily a postsynaptic origin. Neurons showing one or another form of response differ from one another in the relative intensity and time characteristics of excitatory and inhibitory processes interacting on their postsynaptic membranes. In neurons of the phasic type inhibitory processes are dominant over excitatory, while excitatory processes are predominant in neurons of the tonic type.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 17, No. 4, pp. 500–508, July–August, 1985.     

Comparative characteristics of activity in grafted and intact neocortex in slice preparations

Background single unit activity and mixed single and multiunit responses to electrical stimulation of rat's embryonic cortex grafted into the somatosensory cortex of adult rats were investigated in a slice preparation. The relative number of neurons exhibiting background activity in the grafts was higher than in slices of intact cortex (23 and 6%, respectively), however, the portion of neurons responding to electrical stimulation of areas of neighboring neocortex in the recipient was lower than in intact cortex. The latent periods of population responses in the grafts were consistently longer than in those in intact neocortex (19.4±5 and 5.8±1.1 msec, respectively), although the extreme values coincided. The duration of population responses in the grafts was approximately an order of magnitude longer. The data presented suggests the existence of local connections between the graft and the brain of the recipient and shows weakness of inhibitory processes in the grafts. A functional integration of graft and brain in recipients with craniocerebral trauma was demonstrated.Institute of Biophysics, Academy of Sciences of the USSR, Pushchino, Moscow. Institute of Neurosurgery, Ministry of Public Health of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 3, pp. 273–280, May–June, 1991.     

Single unit activity related to acoustic stimulus meaning in the cat auditory cortex during instrumental food reflex

Responses of 93 neurons to isolated presentation of a single click and a series of 10 clicks with following frequency of 1000 Hz and responses of 66 neurons after the click had become a positive conditioned stimulus, and a series of 10 clicks had become a differential, negative stimulus, were investigated in chronic experiments on cats. Formation and realization of differential inhibition of an instrumental food reflex was shown not to lead to strengthening of inhibition in the auditory cortex, and the process of differential inhibition itself within the primary auditory cortex is not essentially an inhibitory process. Identical changes were found in responses of auditory cortical neurons to both positive and negative conditioned stimuli after training, evidence that neurons of the primary auditory cortex play a similar role in realization of the instrumental reflex and in its differential inhibition. It is suggested that the presence of groups of neurons responding by excitation or inhibition only to presentation of a stimulus with definite informative value is of great importance for differentiation.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukranian SSR, Kiev. Translated from Neirofiziologiya, Vol. 17, No. 2, pp. 212–221, March–April, 1985.     

Increase in the sensitivity of rabbit sensomotor cortex neurons to gamma-aminobutyric acid under the influence of diazepam (microiontophoretic study)]

A study was made of the action of diazepam on the effects of the gamma-aminobutyric acid (GABA) applied electrophoretically to the neurons of the sensory-motor rabbit cortex. It was shown that diazepam intensified the depressive action of GABA on the spontaneous neuronal activity and the prolonging action of GABA on the duration of the inhibitory phase in the neuron responses to the afferent and direct stimulation of the cortex. Diazepam failed to alter the neuron response to glycine, glutamate and acetylcholine applied microelectrophoretically. It is supposed that diazepam increased the sensitivity of the receptors of the post-synaptic membrane of the neuron to GABA.     

Neuronal response in an epileptically excited isolated cortical slab to single electrical stimuli

Neuronal response to single stimuli was investigated in a cortical slab isolated from immobilized cats before, during, and after onset of induced epileptic states. Neurons of the isolated cortical slab were found to generate EPSP and paroxysmal depolarizing shifts (PDS) in membrane potential (MP) during the development of generalized epileptoid activity; these occurred together with refractory periods. Duration of the latter corresponds with the PDS plateau and repolarizing shifts in MP. Single electrical stimuli induced gradual alteration in PDS as these shifts developed. Neurons still maintain their ability to generate PDS arising in response to presentation of single stimuli once ictal activity has ceased. Postsynaptic response is not thought to play a decisive role in the genesis of epileptoid activity. Nonspecific factors and especially alterations in the concentration of electrogenic ions apparently contribute to this phenomenon.I. I. Mechnikov State University, Odessa. Translated from Neirofiziologiya, Vol. 21, No. 2, pp. 198–204, March–April, 1989.     

Responses of rabbit visual cortical neurons to intracortical electrical stimulation

Responses of rabbit visual cortical neurons to single and repetitive intracortical electrical stimulation were investigated. The stimulating electrode was located 0.7–1.2 mm away from the recording electrode. Response thresholds to single stimulation were as a rule 150–180 µA, whereas to series of stimuli they were 30–60 µA. The latent period to the first spike averaged 5–15 msec but the probability of the initial discharge was very low, namely 3–6%. With an increase in current intensity the duration of the initial inhibitory pause was increased in half of the neurons responding to it, whereas in the rest it was unchanged. After presentation of series of stimuli spontaneous activity was enhanced for a short time (4–6 sec). In about half of the cells the same kinds of discharge dynamics were observed in response to repetitive stimulation (frequency 0.25 Hz) as in responses to light, but more neurons with sensitization of discharge and fewer "habituating" neurons took part in responses to electrical stimulation. It is postulated that stimulation of a given point of the visual cortex evokes excitation of a local neuron hypercolumn and inhibition of neighboring cell columns.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 15, No. 4, pp. 412–419, July–August, 1983.     

Characteristics of poststimulus and lateral inhibition in neurons of cat primary auditory cortex

Experiments using intracellular recording of potentials from neurons of the primary auditory cortex of cats anesthetized with pentobarbital showed that under the influence of tones of characteristic frequency for the neuron under test, or of electrical stimulation of nerve fibers of the spiral ganglion, innervating the center of the receptive field of the neuron, transient excitation of the latter is followed by the development of prolonged (20–250 msec) inhibition. The cause of this inhibition is an IPSP arising in the neuron after the action potential. On the basis of data showing a close connection between inhibition and the preceding spike it is concluded that it arises through the participation of a mechanism of recurrent inhibition. During the action of tones of uncharacteristic frequency or electrical stimulation of the peripheral part of the receptive field of the neuron, a response consisting of EPSP-IPSP arises in the neuron. This IPSP is accompanied by inhibition of spontaneous activity of the neuron and its responses to testing stimulation. It has been shown that this inhibition is lateral in its genesis. Characteristics of these two types of inhibition are given.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 2, pp. 194–201, March–April, 1984.     

Responses of neurons in cat primary somatosensory cortex to repetitive stimulation of vibrissae

Extra- and intracellular responses of neurons in the primary somatosensory cortex to repetitive mechanical stimulation of the vibrissae at different frequencies were studied in unanesthetized curarized adult cats. Unlike responses to electrical stimulation of the combined afferent input (the infraorbital nerve) spike discharges of neurons in response to vibrissal stimulation can reproduce rather higher frequencies of stimulation and their initial character changes more often in the course of the repetitive series. Most cortical neurons were characterized by limitation of the area of their peripheral receptive fields with an increase in the frequency of adequate repetitive stimulation. A group of cortical neurons was distinguished by its ability to respond to high-frequency stimulation and to generate burst discharges. Comparison of the frequency characteristics of spike responses of these cells and of inhibitory synaptic action in other cortical neurons led to the conclusion that this group of cells thus distinguished may be inhibitory cortical neurons. The role of interaction between excitatory and inhibitory processes arising in cortical neurons during repetitive stimulation of different areas of their receptive fields is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 14, No. 2, pp. 164–171, March–April, 1982.