Role of cortical inhibition in heterosensory interaction of neurons of the cat sensorimotor cortex

Background and evoked neuronal activity in the cat sensorimotor cortex was recorded under a-chloralose anesthesia. Pairs of heterogeneous stimuli were applied, spaced at intervals of 0, 100, 200, 300, and 400 msec. A clicking sound, flashing light, and electroshock to the contralateral forepaw were used as stimuli. Partial or complete blockade of response to test stimuli presentations spaced 100–200 msec apart were observed when using stimulation of varying modality. The greatest test response was recorded at interstimulus intervals of 200–300 msec. Intracellular mechanisms of heterosensory interaction were investigated by applying the inhibitory transmitter antagonist picrotoxin microiontophoretically to the test cell to produce local attenuation of inhibitory effects. This substance also reduced the duration of blockage following the conditioning stimulus and the occurrence of peak level test response at a lower interstimulus interval than in the controls. Either a consistent increase in the number of spikes per response at one of the interstimulus intervals or a uniform reinforcement in unit response to several different interstimulus intervals were observed in a proportion of the cells. The contribution of intracortical inhibitory influences to the mechanisms of heterosensory interaction on neurons of the cat sensorimotor cortex is discussed in the light of our findings.A. A. Ukhtomskii Institute of Physiology, A. A. Zhdanov State University, Leningrad. Translated from Neirofiziologiya, Vol. 19, No. 2, pp. 147–156, March–April, 1987.     

Role of intracortical inhibition in orientation tuning dynamics in the cat striate cortex neurons

A suggestion about the leading role of GABA-induced intracortical inhibition in the dynamics of orientation tuning (OT) of the cat striate cortical neurons was tested in acute experiments before and during the local blockade of their inhibition by iontophoretic application of bicucculine. In the course of the investigation of these dynamics, with the use of a temporal scanning method, two types of neurons differing in the inhibition blockade-induced OT changes were found. In the neurons of the first type (57%), bicuculline induced the OT dynamics or enhanced it, if it pre-existed before the bicuculline application. In the neurons of the second type (43%), bicuculline strongly reduced or eliminated the dynamic shift of a preferred orientation. These results mean that under normal conditions the inhibition stabilizes and sharpens OT in some cells, while in other cells, in contrast, it causes the OT dynamics. The following mechanisms may underlie the observed effects: an elimination of the inhibition originating from lateral non-isoorientational excitatory inputs of a receptive field; an inhibition of these inputs via the adjacent interneurons activated by a powerful discharge of the examined neuron; a long-term afterhyperpolarization of the neuron, and the dynamics of the excitatory and inhibitory zones of the receptive field.Neirofiziologiya/Neurophysiology, Vol. 27, No. 2, pp. 100–109, March–April, 1995.     

Pharmacological analysis of conditioning in sensorimotor cortex neurons in a model

In awake mobile rabbits, with electrodes implanted in the medial lemniscus, midbrain tegmental reticular nucleus, and pyramidal tract, combined stimulation of two brain of two brain structures resulted in elaboration of conditional connections in sensorimotor cortex neuronal populations. The main criterion of the conditioning was the appearance of changes in the neuronal activity on omission of the second stimulus. These changes represented a complex of electrical events, some of which were similar to and others different from the evoked responses to the second stimulus. Application of atropine, sulfate, chlorpromazine hydrochloride, serotonin creatinine sulfate, and gamma-aminobutyric acid (GABA) to the cortex at the site of the recording exerted a modulating effect on the conditional neuronal activity patterns. Of the above substances, GABA and atropine had the most pronounced effect. The GABA removed the short-latency components of the conditional changes which were similar to evoked responses. The atropine abolished the long-latency changes which differed from evoked responses.     

Activation of glutamate ionotropic connections of sensorimotor cortex neurons during conditioning

Changes in conditioned impulse reactions of neurons in sensorimotor cortex were studied during microiontophoretic application of glutamatergic and GABA ergic agonistic and antagonistic drugs. It was shown that ionotropic glutamate receptors (AMPA and NMDA) are activated by a conditioned stimulus. Not only large pyramidal neurons of deep cortical layers but surrounding short-axon inhibitory interneurons are involved in the reaction. It was shown that the activity of pyramidal neurons is under a constant inhibitory control from surrounding interneurons. This inhibition is involved in organization of excitatory cortical responses during conditioning.     

Dendritic action potentials of pyramidal tract neurons in the cat sensorimotor cortex

The intracellular activity of pyramidal tract neurons was studied during electrical stimulation of ventrolateral and ventroposterolateral thalamic nuclei in acute experiments on cats immobilized by myorelaxants. Somatic action potentials were observed and spontaneous spikes were also produced by single and rhythmic stimulation of the thalamic nuclei at the rate of 8–14 Hz, by iontophoretic application of strychnine, and by intracellular depolarizing current pulses. These potentials had a relatively low and variable amplitude of 5–60 mV and are presumed to be dendritic action potentials. It is postulated that these variable potentials arise in the dendrites of pyramidal neurons with multiple zones generating such activity. No interaction was observed where somatic and dendritic action potentials occur simultaneously. The possible functional role of dendritic action potentials is discussed.I. S. Beritashvili Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 18, No. 4, pp. 435–443, July–August, 1986.     

Changes in trace reactions of sensorimotor cortex and putamen neurons as affected by haloperidol

Experiments on conscious rabbits were made to elaborate motor conditioned reflexes through pairing stimuli with electrocutaneous reinforcement applied every 30 s. Neuronal activity in the sensorimotor cortex and putamen was recorded during formation and reproduction of the conditioned reflexes before and after haloperidol injection (0.2 mg/kg i. v.). In the putamen, haloperidol increased the number of neurons exhibiting trace conditioned activity and made the intensity and duration of these processes rise. The changes seen in the sensorimotor cortex were opposite in nature. Inhibition of trace conditioned activity in the sensorimotor cortex depended mainly on the decreased amplitude of the reaction conditioned component. The role of the dopaminergic system in the interaction of the neostriatum and sensorimotor cortex and in formation and reproduction of trace conditioned activity of both the structures is discussed.     

Inhibition in the neurons of the somatosensory cortex and the possibility of intracortical propagation of excitation

Extra- and intracellular leads were used to study the reactions of neurons in the pyramidal tract (PT) of the cat brain to antidromic and afferent effects. It was shown that afferent activation of PT neurons proceeds heterogeneously. Three types of PT neurons were identified, successively involved in the impulse response to afferent stimulation. By means of paired stimuli we determined the heterogeneous changes in sensitivity of late reacting PT neurons. It was found that, under certain conditions, the different IPSP evoked by afferent stimulation or PT stimulation do not prevent the appearance of impulse responses to secondary synaptic activation. A conclusion was drawn from these experiments on the localization of the excitatory intracortical terminals on the somas of the PT neurons and on the limited effect of inhibitory processes upon intracortical propagation of the afferent signal reaching the cortex. A functional scheme of intracortical PT neuron links is presented.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the USSR, Kiev. Translated from Neirofiziologiya, Vol. 3, No. 5, pp. 465–473, September–October, 1971.     

Ultrastructure of sensorimotor cortex neurons in the progeny of rats receiving alcohol during pregnancy

Dynamics of ultrastructural changes in the sensomotor cortex neurons has been studied on the 21st, 30th and 60th days of life in offspring born by the rats given 20% alcohol (2 g/kg) during pregnancy. Moderate antenatal alcoholization produces certain disturbances in the ultrastructure of the cortical neurons and their dendrites. This is manifested as presence of retardation signs in maturation of nervous cell populations, as dystrophic changes in the neurons and their dendrites and display of reparative character with their own dynamics in the postnatal period of ontogenesis. The first two categories of the ultrastructural changes in the cortical neurons are more manifested at early stages of the postnatal development of the offspring, and the reparative processes--at the age of two months. Despite the presence of the reparative shifts, the dystrophic changes of the neurons of hypoxic character are present up to the period of sexual maturation. This demonstrates that the antenatal alcoholic intoxication in the offspring is manifested in the postnatal ontogenesis for a long time.     

Analysis of the layer distribution of transcallosal responses in the sensorimotor cortex of kittens in the 1st month of life

In experiments on 23 kittens ageing between 1-30 days, anaesthetized by barbiturate and immobilized by diplacine, studies have been made on the distribution of transcallosal responses (TCRs) along the whole diameter of the sensorimotor cortex. In order to obtain more accurate data on localization of the sources and drains of extracellular current vertical component, a method of double graphic differentiation was used. It was shown that in 1-2-day kittens TCRs have a positive oscillation form throughout all the depth of recording. During the 1st week, TCRs from the cortical surface acquired a positive-negative configuration, remaining mostly positive in deeper layers. At this ontogenetic stage, the drain of positive-negative oscillation is focused in the layer I. In 2-3-week kittens, positive-negative potentials on the surface were transformed into negative-positive responses in deep layers. The drains of this deep negative component were localized in the layers III and V-VI. On the 4th week, positive-negative TCRs on the surface changed into negative-positive potentials at various depths depending on the spatial position of the recording point. The drain of deep-laid negative component in the focus of maximum activity was found in the layer V, out of its boundaries--in the layers II-III. Ontogenetic dynamics was revealed of current drains localization of both TCRs components in the sensorimotor cortex in new-born kittens.     

Effect of a vasopressin analog on the chemoreactive properties of sensorimotor cortex neurons

Subcutaneous injection of 10 micrograms desglycilargininvasopressin (DG-AVP) does not alter the mean frequency of background unit activity of sensorimotor cortical neurons. However, the pattern of impulse activity is essentially changed. At the same time the reactions of sensorimotor cortical neurons to microiontophoretic administration of acetylcholine and noradrenaline experience definite changes. It is suggested that the DG-AVP-induced changes in chemoreactive properties of neurons underlie the effect of this peptide on the learning and memory.     

Influence of the sensorimotor cortex on single neurons of the nucleus gracilis in the cat

The aim of this study was to investigate the functional role of the cortical projections to gracile nucleus. In unanesthetized cats single nuclear units projecting to the thalamus were tested for microstimulation of cortical foci (area 4) able to evoke single joint movements in contralateral hindlimb. A very significant percentage of gracile cells was influenced, very often in excitatory manner, if their receptive field was overlaying or very close to the joint controlled by a given cortical focus. Conversely, when the location of the receptive field was more distant, the percentage of responses and the incidence of excitatory effects decreased, inhibitions occurring more frequently. From a functional point of view, such an organization of the cortico-gracile control could be effective in modulating transmission of exteroceptive information from the region of the motor target (facilitation) as well as from adjacent ones (suppression). This arrangement could provide an higher resolution of afferent messages, in relation with the cortically induced movements.     

Origination and development of sensorimotor, associative and transcallosal responses in kittens in ontogeny

In acute experiments on 3-30-day kittens, recording the evoked potentials, studies have been made on the development and maturation of sensorimotor parietal associative and transcallosal responses (TCR). At early ontogenetic stages, these TCR are presented by single negative oscillation, strictly localized, with a large latent period and long duration. During postnatal life, the duration of the latent period decreases, whereas the area of the evoked potentials increases. Investigation of the electrical responses in focus of maximum activity in sensorimotor and parietal associative regions in kittens of all age groups revealed earlier activation of the projectional areas and later maturation of the associative inputs.     

Trace rhythm recruitment by the neurons of the rabbit sensorimotor cortex in old age]

Spectral analysis (ACG and gSP) of the impulse activity of the neurones of the old rabbits sensorimotor cortex allowed to reveal a trace recruitment of the rhythm--CR analogue to time--in after-action f rhythmic stimulation. Connection was established between the number of presented series of periodic electrocutaneous stimulation and expressiveness of the trace rhythm recruitment depending on the animals age. Trace rhythm recruitment took place slower in old animals (54-56 months) than in young ones (up to 1 year), chiefly in 2-3 experimental days after 2-4 series of rhythmic stimulation and was preserved in a small percent of cases the next day after stimulation. In the background activity of a number of neurones an initial periodicity was discovered, which was intensified under the influence of stimulation by another frequency, or the initial rhythm was extinguished, and stimulation rhythm was reproduced. Periodical stimulation in very old animals (66-85 months) practically did not evoke plastic reconstructions of the cortical neurones. Under the influence of the stimulation a non-specific trace increase of the frequency of neurones background activity of the old animals was observed. The revealed characteristics of plastic neurones properties may testify to projected disturbances of mnestic processes at definite age stages of normal aging.     

The tuning of striate neurons to cross-like figures during local blockade of intracortical inhibition]

Many neurons in the cat primary visual cortex reveal sensitivity to cruciform and corner figures as well as to local orientation discontinuities. We investigated this sensitivity in 85 V1 neurons before and after the local blockade of GABA(A)ergic inhibition by microiontophoretic application of bicuculline and observed two opposite effects: a decrease or disappearance of sensitivity to crosses in about half of the neurons and its increase or appearance in about one third of the units. The results indicate substantial and drastically different contribution of intracortical inhibition to sensitivity to line-crossings in the visual cortical neurons. Some possible mechanisms of this difference are discussed.     

Activity of sensorimotor cortex neurons during a dopaminergic transmission block in cats performing conditional reflex

Activity of sensorimotor cortex neurons was recorded in chronic experements on cats trained to perform instrumental conditional reflex; records were made before, during, and after isolated iontophoretic applications of haloperidol or glutamate, or their combined application. Haloperidol was shown either to facilitate or to inhibit the background and evoked (related to acoustic stimulation and motor response) spike activity of cortical neurons. Aftereffects of haloperidol were observed too; they were still expressed 10–15 min after the cessation of the iontophoresis. Combined haloperidol and glutamate application was followed by a sharp suppression of the evoked responses potentiated earlier by glutamate. An adenylatecyclase system is supposed to mediate the facilitation evoked by glutamate application. Some modulators, including dopamine, probably activate adenylatecyclase and in this way ensure facilitation of the glutamate-induced responses.Neirofiziologiya/Neurophysiology, Vol. 26, No. 5, pp. 347–355, September–October, 1994.     

Effect of vasopressin and enkephalin analogs on the chemoreactive properties of the sensorimotor cortex neurons in rats

On immobile rats it has been shown that subcuteneous injection of two different neuropeptides causes different distribution of activating, inhibiting and areactive cells resulting from microionoforetically administrated acetylcholine and noradrenaline without altering the mean frequency of the background unit activity sensorimotor cortical neurons. At the same time the alteration in the pattern of neurons impulse activity has been revealed, which acquires the character of packet activity with a specific packet length of 2-3, 4-6, 7-10 impulses. Depending on the injected neuropeptide reliable but almost contrary effects of the packet activity alterations have been observed. These effects have been suggested to result from the alteration of the chemoreactive properties of the neuron membranes and the corresponding reorganisations of interneuron attitudes.     

Comparative analysis of the interactions between spontaneous active neurons of the sensomotor cortex of kittens and adult cats

The character of functional interneuronal relations in the sensorimotor cortex during spontaneous neural activity in kitten and adult cats immobilized with d-tubocurarine, was studied by the method of cross-correlations of two impulse series. The data obtained by computation revealed specific age-related interneuronal connections in investigated groups of animals. In kitten aged up to 10 days, the highest percentage of the functional connections was observed which were established mainly due to the influence of a common source. In other groups of animals (kittens of 20, 30 days of postnatal life, adult cats) the common source did not play a significant role in the formation of interneuronal connections. The results showed that inhibitory connections between neurones-are established to the end of the first month of the postnatal life.     

Analysis of the reactivity of the sensorimotor neurons of the rat cerebral cortex to acetylcholine

Several types of cholinoceptive neurons have been identified in rat's sensomotor cortex according to response character to ionophoretical application of acetylcholine. The neurons investigated form continuous range according to duration of the excitatory component of reaction to transmitter application. It has been suggested that the duration of this component reflects the important functional properties of the nerve cell.