Effect of direct and transcallosal stimulation on inhibition of unit activity in the cat association cortex

Inhibition of association cortical neurons (in the form of inhibition of spontaneous activity or of IPSPs) during direct and transcallosal stimulation was studied in cats immobilized with muscle relaxants. The duration of inhibition of stimulation and the number of stimuli. With an increase in the strength of stimulation inhibition deepened to a certain level for a particular neuron, after which it could be further lengthened with an increase in the number of stimuli. In the case of repeated stimulation by volleys of stimuli, very prolonged inhibition developed gradually in the neurons, during which spontaneous activity was inhibited for 2–5 sec. The duration of the IPSP depended on the intensity of stimulation and number of stimuli and its amplitude depended on the intensity and frequency of stimulation and on the number of stimuli. In some cases the amplitude of the IPSP continued to rise after a short volley of stimuli, even after the end of stimulation. An increase in the number of stimuli in the volley lengthened the IPSPs, but their amplitude remained constant throughout the period of stimulation. Prolonged inhibition (up to a few seconds) was connected with the development of a hyperpolarization postsynaptic potential in the neurons. It is suggested that neurons exerting a monosynaptic inhibitory influence on cells of the association cortex may be located in the opposite hemisphere.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 2, pp. 133–141, March–April, 1981.     

Neuronal and synaptic mechanisms of cortical inhibition

The latent periods, amplitude, and duration of IPSPs arising in neurons in different parts of the cat cortex in response to afferent stimuli, stimulation of thalamocortical fibers, and intracortical microstimulation are described. The duration of IPSPs evoked in cortical neurons in response to single afferent stimuli varied from 20 to 250 msec (most common frequency 30–60 msec). During intracortical microstimulation of the auditory cortex, IPSPs with a duration of 5–10 msec also appeared. Barbiturates and chloralose increased the duration of the IPSPs to 300–500 msec. The latent period of 73% of IPSPs arising in auditory cortical neurons in response to stimulation of thalamocortical fibers was 1.2 msec longer than the latent period of monosynaptic EPSPs evoked in the same way. It is concluded from these data that inhibition arising in most neurons of cortical projection areas as a result of the arrival of corresponding afferent impulsation is direct afferent inhibition involving the participation of cortical inhibitory interneurons. A mechanism of recurrent inhibition takes part in the development of inhibition in a certain proportion of neurons. IPSPs arise monosynaptically in 2% of cells. A study of responses of cortical neurons to intracortical microstimulation showed that synaptic delay of IPSPs in these cells is 0.3–0.4 msec. The length of axons of inhibitory neurons in layer IV of the auditory cortex reaches 1.5 mm. The velocity of spread of excitation along these axons is 1.6–2.8 msec (mean 2.2 msec).A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 3, pp. 394–403, May–June, 1984.     

Connections of neurons of the cat somatosensory cortex with the thalamic relay nuclei

Of 103 neurons in the rostral part of the posterior sigmoid gyrus of the cat cortex 30 responded to stimulation of the ventro-posterolateral and ventrolateral nuclei of the thalamus (VPL and VL), 42 responded to stimulation of VL only, and 31 to stimulation of VPL only. It was shown by intracellular recording that stimulation of VPL induces a spike response with or without subsequent IPSPs in some neurons and an initial IPSP in others. The spike frequency of single neurons reached 60/sec, but the IPSP frequency never exceeded 10–20/sec. Stimulation of VL was accompanied by: a) antidromic spike responses; b) short-latency monosynaptic EPSPs and spikes capable of following a stimulation frequency of 100/sec; c) long-latency polysynaptic EPSPs and spikes appearing in response to stimulation at 4–8/sec; d) short-latency IPSPs; e) long-latency IPSPs increasing in intensity on repetition of infrequent stimuli. It is concluded that the afferent inputs from the relay nuclei to neurons of the somatosensory cortex are heterogeneous. An important role is postulated for recurrent inhibition in the genesis of the long-latency IPSPs arising in response to stimulation of VL, and for direct afferent inhibition during IPSPs evoked by stimulation of VPL. It is shown that the rostral part of the posterior sigmoid gyrus performs the role of somatic projection and motor cortex simultaneously.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 3, pp. 245–255, May–June, 1972.     

Inhibitory effects of reticulospinal fibers of the lateral funiculus on neurons of thoracic spinal reflex pathways

Experiments on anesthetized cats with partial transection of the spinal cord showed that reticulo-spinal fibers in the ventral part of the lateral funiculus participate in the inhibition of polysynaptic reflexes evoked by stimulation of the ipsi- and contralateral reticular formation. The reticulo-fugal wave in the ventrolateral funiculus evoked comparatively short (up to 70 msec) IPSPs in some motoneurons of the internal intercostal nerve investigated and at the same time evoked prolonged (up to 500 msec) inhibition of IPSPs caused by activation of high-threshold segmental afferents. This wave also led to the appearance of IPSPs in 14 of 91 (15.5 %) thoracic spinal interneurons studied. The duration of these IPSPs did not exceed 100 msec; meanwhile, segment excitatory responses of 21 of 43 interneurons remained partly suppressed for 120–500 msec. It is concluded that the inhibitory action of the lateral reticulo-spinal system on segmental reflexes is due to several synaptic mechanisms, some of them unconnected with hyperpolarization of spinal neurons. The possible types of mechanisms of this inhibition are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 2, pp. 162–172, March–April, 1978.     

Monosynaptic inhibitory postsynaptic potentials of cortical neurons

Monopolar intracortical stimulation of the auditory cortex was carried out in cats immobilized with D-tubocurarine. A macroelectrode (tip diameter 100 µ) or a microelectrode (tip diameter 10–15 µ) was used for stimulation. In both cases, besides excitatory responses, primary IPSPs with latent periods of 0.4–1.2 and 1.4–6.0 msec were recorded in cortical neurons close to the point of stimulation. The first group of IPSPs are considered to be generated in response to direct stimulation of bodies or axons of inhibitory cortical neurons, i.e., monosynaptically. The amplitude of these IPSPs varied in different neurons from 3 to 15 mV, and their duration from 4 to 150 msec. Additional later inhibitory responses were superposed on many of them. Of the IPSPs generated in auditory cortical neurons in response to stimulation of geniculocortical fibers 1.5% had a latency of 0.8–1.3 msec. They also are assumed to be monosynaptic. It is concluded that the duration of synaptic delay of IPSPs in cortical neurons and spinal motoneurons is the same, namely 0.3–0.4 msec. Axons of auditory cortical inhibitory neurons may be 1.5 mm long. The velocity of impulse conduction along these axons is 1.6–2.8 m/sec. The genesis of some special features of IPSPs of cortical neurons is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 7, No. 5, pp. 458–467, September–October, 1975.     

Analysis of long cortical evoked potentials

Evoked potentials arising in the motor cortex in response to its direct stimulation (dendritic and slow negative potentials), to stimulation of the ventrolateral (primary response) and intralaminar (nonspecific response) thalamic nuclei, and to stimulation of the pyramidal tracts (antidromic response), and also postsynaptic responses of neurons corresponding to them were studied in acute experiments on curarized cats. Evoked potentials arising in response to direct cortical stimulation and also to stimulation of the specific and nonspecific thalamic nuclei and pyramidal tracts were recorded from the same point of the motor cortex, and the corresponding intracellular responses were recorded from the same neuron. Slow negative potentials arising under these conditions of stimulation and the IPSPs corresponding to them were shown to have an identical time course. The results show that slow negative potentials are a reflection of hyperpolarization of pyramidal neurons. It is suggested that the individual components of responses evoked by direct stimulation of the cortex and thalamic nuclei have a common genesis.I. S. Beritashvili Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 14, No. 2, pp. 115–121, March–April, 1982.     

Effects of applying electrical stimulation to the locus coeruleus on neuronal activity in the parietal association cortex

It was shown during experiments on cats undergoing surgery under ketamine-induced anesthesia and immobilized with myorelaxin that applying trains of stimuli to the locus coeruleus (LC) produces an effect on 79% of parietal cortex neurons. This manifests as inhibition lasting 300–700 msec or a 16–32% decline in the activity rate of neurons with background activity. Hyperpolarization of 5–7 mV lasting 120–500 msec preceded by a latency of 30–90 msec was noted in such neurons as well as "silent" cells during intracellular recording. Duration of the inhibitory pause in neuronal background activity induced by transcallosal stimulation (TCS) increased by 50–200 msec under the effects of conditioned stimuli applied to the LC. Duration of the IPSP triggered by TCS likewise increased (by 50–100 msec) under the effects of LC stimulation. It was concluded that the effects of stimulating the LC on neuronal activity in the parietal cortex may manifest either directly, as inhibition of background activity and hyperpolarization, or else as modulation of influences exerted by other neurotransmitters.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 22, No. 4, pp. 486–494, July–August, 1990.     

Inhibition in hippocampal pyramidal neurons during peripheral stimulation

Responses of hippocampal pyramidal neurons were investigated intracellularly in unanesthetized rabbits immobilized with tubocurarine. A single stimulus, applied to the sciatic nerve, evoked prolonged (up to 2.5 sec) hyperpolarization of the cell membrane, accompanied by inhibition of action potentials. The latent period of the evoked hyperpolarization was 48±16.4 msec, and its amplitude 2.5±1.9 mV. In some neurons the development of hyperpolarization potentials was preceded by excitation. The suggestion is made that hyperpolarization of the membrane of pyramidal cells during peripheral stimulation is manifested as an inhibitory postsynaptic potential (IPSP), generated with the participation of hippocampal interneurons. The possibility of prolonged tonic action of interneurons from outside as a cause of prolonged inhibition of the pyramidal neurons is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 1, No. 3, pp. 278–284, November–December, 1969.     

Postsynaptic inhibition in the general cortex of the turtle forebrain

Postsynaptic inhibition in the general cortex of the turtle forebrain was investigated by recording unit activity intracellularly. Depending on the type of IPSPs recorded in response to electrical stimulation of the contralateral optic nerve and cortical surface the neurons were subdivided into three groups: 1) with long direct IPSPs, 2) with long and short direct, and also recurrent IPSPs, 3) with short direct and recurrent IPSPs. It is concluded that inhibitory pathways of the short direct and recurrent IPSPs have a common final component, a stellate interneuron. Compared with the recurrent collaterals of the principal neurons, the direct afferents make contact with more distal portions of the dendrites of this cell. Synapses formed on dendrites of the principal neurons by axons of the stellate cells are nearer to the soma than synapses responsible for generation of the long direct IPSP.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 5, No. 4, pp. 375–383, July–August, 1973.     

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.     

Possible interaction between synaptic and pacemaker mechanisms of electrical activity in bursting neurons of Helix pomatia

Membrane hyperpolarization induced by short pulses of inward current, by stimulation of the anal nerve, which leads to the appearance of a long IPSP in the neuron, and developing during the appearance of spontaneous IPSPs in the neuron was investigated in neuron RPa1 ofHelix pomatia. Short-term hyperpolarization of the neuron membrane by an inward current (10 msec) led to the development of self-maintained (regenerative) membrane hyperpolarization lasting several seconds. The amplitude and duration of regenerative hyperpolarization increased with an increase in amplitude and duration of the pulse of inward current. The time course of IPSPs arising spontaneously in the neuron and in response to stimulation of the anal nerve was similar to that of regenerative hyperpolarization evoked by a pulse of inward current. It is suggested that regenerative hyperpolarization associated with activation of endogenous mechanisms of regulation of the bursting activity of the neuron may be due not only to short-term membrane hyperpolarization of the test neuron by the electric current, but also to hyperpolarization occurring during IPSP generation.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 1, pp. 67–74, January–February, 1981.     

Responses of the neurons of the cortical secondary auditory area to acoustic and non-acoustic stimuli in cats

The responses of the cortical secondary auditory area (AII) to the non-acoustic stimuli (electrical stimulation of the skin in the vibrissae area and light flash) and their combination with acoustic stimulation (sound click or tone) were studied in experiments on cats anesthetized by kalipsol using extra- and intracellular recording. Of the total number of neurons, 69% of the units generating spike responses to the acoustic stimulation responded to the non-acoustic stimulation too. The responses to the modal-nonspecific stimulation, as a rule, were weak and variable; they were mostly represented by a tonic change in the neuronal discharge frequency. The nonspecific stimulation evoked primary excitatory and inhibitory postsynaptic potentials in 77% and 20% of the examined neurons, respectively. We found that synaptic effects of the nonspecific and specific stimulations interact with each other, ensuring considerable modulation of the latter (mostly a significant facilitation resulting from the EPSP summation and suppression of an inhibitory component of the response to acoustic stimulation). Possible participation of the midbrain reticular formation in the transmission of the modal-nonspecific influences to the cortical neurons is considered; stimulation of this structure evoked responses similar to those evoked by the modal-nonspecific sensory stimuli.Neirofiziologiya/Neurophhysiology, Vol. 26, No. 5, pp. 356–364, September–October, 1994.     

Neuronal response in nucleus reticularis thalami and neighboring thalamic structures to natural stimulation during chronic experiments on cats

Spike response was investigated in 104 neurons of the nucleus reticularis thalami (R) and adjoining thalamic nuclei to acoustic, tactile, and visual stimuli during chronic experiments on cats. Of the test neurons, 29% responded to acoustic stimulation and 11% showed no preference in relation to different acoustic stimuli. Minimum latencies of response to sounds measured 12–37 msec in excitatory and 18–27 msec in inhibitory cells. Duration of excitation produced by acoustic stimuli reached 50–250 msec; inhibition lasted 27–190 msec. Most cells belonging to this nucleus were excited by different stimuli; the proportion of inhibitory neurons did not exceed 4–10%.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 4, pp. 451–461, July–August, 1989.     

Unit responses of the somatosensory cortex of the waking cat to stimulation of the ventro-posterolateral thalamic nucleus

Unit responses in the primary somatosensory projection cortex to stimulation of the ventro-posterolateral thalamic nucleus were investigated by extra- and intracellular recording in chronic experiments on cats. Short-latency spike responses of 71.3% of recorded neurons appeared after not more than 4 msec. It is concluded that activation of neurons in this area of the cortex is chiefly monosynaptic and disynaptic. Besides participating in the initial response to the stimulus, one-quarter of the neurons generated after-discharges 120–314 msec later. These after-discharges are based on rebound after IPSPs and additional synaptic activation. Initial inhibition may appear 1.5 msec after stimulation of the ventro-posterolateral nucleus, evidence against the participation of recurrent collaterals in the formation of these IPSPs.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 5, No. 4, pp. 348–354, July–August, 1973.     

Unit responses in the auditory cortex to stimulation of geniculocortical fibers

Extracellular and intracellular single unit responses of neurons of the auditory cortex to electrical stimulation of geniculocortical fibers (GCF) were recorded in experiments on cats immobilized with tubocurarine. The latent period of responses of 15% of neurons to GCF stimulation was 0.3–1.5 msec. It is postulated that they were excited anti-dromically. The latent period of spikes generated by neurons responding to GCF stimulation orthodromically varied from 1.6 to 12 msec. In 28.6% of neurons the latent period was 1.6–2.5 msec. It is postulated that these neurons were excited monosynaptically. Intracellular recording revealed primary IPSPs in response to GCF stimulation in 63.3% of neurons, a brief EPSP followed by a prolonged IPSP in 17.7%, an EPSP-spike-IPSP complex in 12.3%, and subthreshold EPSPs in 7% of neurons. The latent period of the primary IPSPs varied from 1.8 to 11 msec, being 1.8–3.7 in 72%, 3.8–5.7 in 20.0%, and 5.8–11 msec in 8.0% of neurons. The latent period of responses beginning with an EPSP was 1–4 msec (mean 1.8 msec). Orthodromic responses arising 3–10 msec after the antidromic response, and consisting of 3–5 spikes, were recorded in some antidromically excited neurons. Hypotheses regarding the functional organization of the auditory cortex and mechanisms of inhibition in its neurons are put forward on the basis of the results obtained.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 3, pp. 227–235, May–June, 1972.     

Synaptic mechanisms controlling receptor unit activity in the stretch receptor—Abdominal ganglionic chain system of the crayfish

Inhibitory control over activity of the receptor neuron was investigated in a preparation of the stretch receptor and abdominal ganglionic chain in crayfishes. Potentials were recorded intracellularly from receptor neurons and neurons of the abdominal ganglion, and extracellularly from the dorsal roots. IPSPs appeared in the receptor neuron in response to stimulation of that same neuron or of the abdominal ganglionic chain. The relationship between spikes at the input and output of the inhibitory neuron varied over a wide range depending on the functional state of the neuron. A linear relationship was established between the time before appearance of the IPSP and the duration of the interspike interval of the slowly adapting neuron (SAN) and also between the firing rate of this and the inhibitory neurons during recurrent inhibition. Factors influencing the length of the interspike interval of the SAN on the appearance of an IPSP in it were investigated. It is postulated that summation of potentials evoked by spikes of the SAN and also of potentials evoked by spikes of that neuron, together with local processes evidently of endogenous nature takes place in the inhibitory neuron. IPSPs were recorded from two neurons resistant to strychnine and blocked by picrotoxin on the receptor neuron. The structural and functional organization of the individual elements in the chain of recurrent inhibition and inhibition evoked by stimulation of the abdominal ganglionic chain is discussed.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 5, No. 3, pp. 323–332, May–June, 1973.     

Changes in membrane potential and postsynaptic potentials evoked by strychnine in neocortical neurons

Intracellular responses of neurons of the suprasylvian fissure to intracortical stimulation before and during topical cortical strychnine application was studied in experiments on immobilized, unanesthetized cats (a local anesthetic was used). Untreated cortical neurons responded to intracortical stimulation with a monosynaptic excitatory postsynaptic potential (EPSP) followed by an inhibitory postsynaptic potential (IPSP). Application of strychnine evoked epileptiform population activity and paroxysmal depolarizations of neuronal membrane potentials (MPs), followed by hyperpolarization. Increased hyperpolarizations, and the prolonged duration of their summation were responsible for an increased MP and reduced or abolished tonic spike activity. Intracellular application (as a result of diffusion from the microelectrode) of ethyleneglycoltetraacetate (EGTA) that blocked the calcium-dependent potassium membrane conductance (gK(Ca)) abolished the hyperpolarization. The development of epileptiform activity was accompanied by reduction of the IPSP, and an increase in the monosynaptic EPSP. The role of gK(Ca) and postsynaptic inhibition in epileptogenesis is discussed.I. I. Mechnikov State University, Odessa. Translated from Neirofiziologiya, Vol. 24, No. 6, pp. 684–691, November–December, 1992.     

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.     

Effect of reticular formation on hippocampal neurons (field CA1)

The reaction of field CA₁ hippocampal neurons to stimulation of the reticular formation (RF) with impulses of different frequencies was investigated in experiments on unanesthetized rabbits. The effect of electrical and sensory stimuli was compared and the effect of reticular stimulation on the sensory responses was determined. With an increase in the frequency of RF stimulation, the number of neurons of field CA₁ responding with inhibition of the activity increases. Multimodal neurons of the hippocampus depend on the reticular input to a greater degree than unimodal neurons. Neurons whose activity does not change in response to the effect of sensory stimuli also do not respond to stimulation of the RF. Neurons responding with inhibitory reactions to sensory stimulation show a higher correlation with the effects of RF stimulation than neurons with activation reactions and, especially those with "complex" responses to the effect of sensory stimuli. In a considerable number of hippocampal neurons the responses to sensory stimuli change in the course of 10–15 min after stimulation of the RF. The role of the RF in the organization of the reactions of hippocampal neurons is discussed.Division of Memory Problems, Institute of Biological Physics, Academy of Sciences of the USSR, Pushchino-on-Oke. Translated from Neirofiziologiya, Vol. 3, No. 3, pp. 227–235, May–June, 1971.     

Mechanisms of the effect of diazepam on paroxysmal electrical activity of an isolated cortical slab in cats

The effect of diazepam on paroxysmal global electrical activity of a neuronally isolated slab of auditory cortex and on inhibitory responses of its neurons due to intracortical electrical stimulation was investigated in cats. Diazepam (2 mg/kg, intravenously) caused inhibition of paroxysmal electrical activity and increased the number of inhibited neurons in both the acutely isolated slab and three weeks after isolation, compared with the intact cortex. However, the number of disynaptic responses was reduced under these circumstances, especially in the long-isolated slab. It is postulated that diazepam exerts its action through activation of GABA-ergic inhibitory neurons, by synchronizing inhibition and increasing the duration of the IPSPs. The action of diazepam is manifested first, probably, in the initial links of cortical neuron chains.I. I. Mechnikov Odessa State University. Translated from Neirofiziologiya, Vol. 17, No. 1, pp. 3–10, January–February, 1985.