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.     

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 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.     

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.     

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.     

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.     

Cholinergic neurons in an association cortex slab chronically isolated from the cat

Small numbers of short- and long-axon cholinergic interneurons were revealed on a slab of association cortex three weeks after (neuronal) isolation from the cat by means of a histochemical acetylcholinesterase reaction. Short-axon neurons are located at layers II–VI and take the form of mainly spindle-shaped medium sized cells with their axons forming synaptic terminals on pyramidal and stellate neurons of the isolated section. Typical positioning of cholinergic terminals on the perikaryon and proximal portions of cholinoceptive neuron dendrites was noted. Pyramidal cholinoceptive cells may be classed as noncholinergic cells, whereas stellate cells may be either cholinergic or noncholinergic. Long-axon cholinergic interneurons of different shapes and sizes are situated at layers I and VI. Neuronal axons located in these layers run within fibers of the first and subcortical layers, establishing intracortical connections beyond the confines of the isolated section.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 1, pp. 60–66, January–February, 1989.     

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.     

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.     

Response of cat auditory cortex neurons to tonal stimulation during and after nembutal anesthesia

During acute experiments on 20 cats a comparative study was made of neuronal reaction to a tone, as recorded during the first few hours after administration of Nembutal and after an interval of 10–30 h. No spontaneous activity was seen in 89% of auditory cortex neurons of the anesthetized cats; these produced a sterotyped on- response to the optimal frequency tone. Late neuronal spike discharges at distinct intervals of 100–150 msec appeared in response to the setting up of acoustic stimulation after a brief latent reaction lasting 9–15 msec. It was shown that this stimulation did not produce an off-response in the cortical neurons. When the animals emerged from Nembutal anesthesia, the neurons reacted very differently to the optimal frequency tone. About 76% of the cells produced an on, on-off or off response, while about 21% responded with either tonic spike discharges or total inhibition of these throughout the acoustic stimulation. In unanesthetized cats the vast majority of AI cortical neurons were capable of reacting as long as the stimulus lasted. It is shown how this ability is lost under deep Nembutal anesthetic.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 17, No. 6, pp. 728–737, November–December, 1985.     

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 responses in area 7 of the cat cortex during defensive conditioning

Responses of neurons in area 7 of the parietal association cortex during and after formation of a defensive conditioned reflex to sound were recorded in waking cats. Changes in spike responses of the neurons as a result of the onset of conditioned reflex limb movements were observed in 68% of neurons. Spike responses of neurons formed as a result of learning appeared only if conditioned-reflex limb movements appeared, and they were not observed if, for some reason or other, movements were absent after presentation of the positive conditioned stimulus or on extinction of the reflex. Responses of 46% neurons to conditioned stimulation preceded the conditioned-reflex motor responses by 50–450 msec. The remaining responding neurons were recruited into the response after the beginning of movement. Characteristic spike responses of neurons to the conditioned stimulus appeared 500–900 msec before the beginning of movement and, in the case of appearance of special, "prolonged" motor responses of limb withdrawal, evoked by subsequent reinforcing stimulation.     

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.