Effect of posterior hypothalamic stimulation on neocortical electrical activity in the chronic premesencephalic cat

Chronic experiments were carried out on 19 adult cats after preliminary division of the brain stem at the level of the anterior border of the superior colliculus. High-frequency electrical stimulation of the posterior hypothalamus of these animals caused desynchronization of electrical activity in different parts of the neocortex. The influence of the posterior hypothalamus was predominantly on activity in the frontal zones of the neocortex. It is postulated on the basis of these results that the posterior hypothalamus has an activating effect on the neocortex through the thalamic nuclei.Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 8, No. 1, pp. 47–53, January–February, 1976.     

Formation of "caudate spindles" in the rabbit sensomotor cortex during ontogeny

Electrical activity of the sensomotor and visual areas of the neocortex during stimulation of the caudate nucleus was recorded in young rabbits aged 3–60 days and in adults. Single stimulation of the caudate nucleus was found to cause the appearance of characteristic bursts of spindle-like rhythmic activity ("caudate spindles"), described previously in cats and monkeys, in the adult rabbit cortex. The latent period of the caudate spindle was about 200 msec, its duration 1–3 sec, and the frequency of its oscillations of the order of 12 Hz. Caudate spindles were most marked in the sensomotor cortex of the ipsilateral hemisphere. In rabbits under 10 days old caudate spindles were not found even if the intensity of stimulation was increased many times. Starting from the age of 15 days bursts of rhythmic activity resembling caudate spindles, but with lower frequency (about 8 Hz), longer latent period (up to 350 msec), and also with a higher threshold, appeared in the sensomotor cortex. The definitive type of caudate spindles was established toward the end of the first month of postnatal life, corresponding to the time of formation and complication of conditioned-reflex activity in developing animals.Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 17, No. 1, pp. 11–15, March, 1985.     

Role of the frontal cortex in organizing emotional-behavioral reactions induced by hypothalamic stimulation and natural stimuli

Study of the effects of a functional switching off the sensorimotor neocortex area in cats by means of cooling reveals its inhibitory influence on emotional-behavioral reactions to hypothalamic stimulation. Multiple (up to 12) switchings off of the frontal neocortex are attended with a gradual compensation of its inhibitory function by the activity of other brain structures. On the other hand inactivation of the sensorimotor cortex reduces the ability of natural provoking stimuli to lower the thresholds of goal-directed rage which develops when these stimuli are combined with an electrical stimulation of the hypothalamus. A conclusion has been made on the participation of the frontal neocortex in the systemic organization of estimation of biologically significant stimuli.     

Participation of the posterior hypothalamus in the activity of the ascending activating system]

In chronic experiments on cats with premezencaphalic section of the brain stem electrica stimulation of the posterior hypothalamus caused desynchronization of the electrical activity of the neocortex. After the isolated injury of the posterior hypothalamus a moderate electrical stimulation of the medical part of the midbrain reticular formation failed to cause any pronounced activation of the neocortex. The results obtained indicated an important role of the posterior hypothalamus in the function of the ascending activating system.     

Analysis of evoked potentials from the limbic cortex

In acute experiments on cats we investigated evoked potentials from the cingulate gyrus developed in response to stimulation of somatic and visceral nerves; also potentials from various parts of the hypothalamus, and midbrain reticular formation. We showed that the nonspecific afferent system influences electrical activity in the limbic cortex through hypothalamic pathways. We consider the limbic cortex to be part of the association area of the neocortex and that the associative responses of the cortex are more complex in nature than is usually thought to be the case, and that they are formed under the influence of impulses arriving at the cortex along many specific and nonspecific pathways. The hypothalamo—cingulate system is one of the main systems of cortico—subcortical integration. It plays an important part in regulation of autonomic, somatic, and emotional responses.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 2, No. 5, pp. 451–459, September–October, 1970.     

Responses of pyramidal tract and corticorubral neurons to stimulation of lateral hypothalamic structures in cats

Responses of pyramidal tract neurons and corticorubral and unidentified neurons in the pericruciate area of the cortex to electrical stimulation in the posterior, tuberal, and anterior zones of the lateral hypothalamus and also to electrodermal stimulation of all four limbs were studied in cats anesthetized with chloralose. The proportion of pyramidal tract, corticorubral, and unidentified neurons which responded to hypothalamic stimulation was 73.3, 55.7, and 79.1% respectively. Data on the possibility of monosynaptic activation of some pyramidal tract neurons and unidentified cells were obtained. The presence of less stable and longer-latency responses of corticorubral neurons indicated the absence of a monosynaptic pathway for realization of ascending hypothalamic influences on neurons of the cortical extrapyramidal system. Some cortical neurons responded to stimulation of more than one zone of the hypothalamus. Pyramidal tract neurons and corticorubral neurons with axon collaterals running into the region of the hypothalamus were discovered for the first time. It was shown that most neurons of the pericruciate area of the cortex to which the ascending influence of the hypothalamus is directed have a large bilateral receptive field and respond to electrodermal stimulation of several limbs.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 14, No. 3, pp. 298–306, May–June, 1982.     

Electrophysiological study of the functional connections of the hypothalamus with the forebrain in the tortoise Emys orbicularis

During stimulation of the posterior hypothalamus, the evoked potentials with short latent periods, high amplitude and poor exhaustion by rhythmic stimulation were recorded in the hippocampal cortex. In the piriform cortex, the evoked potentials exhibited longer latent periods and complex configuration. Less readily the evoked potentials appeared in the neocortex, their latency being very large. During stimulation of the anterior hypothalamus, maximum activity was also localized in the hippocampal cortex. The data obtained indicate close connection between hypothalamic structures and the hippocampal cortex. The latter is presumably the main projectional area for the ascending afferentation from the hypothalamus.     

Role of the caudate nucleus in the development of evoked synchronized activity

Synchronized activity (spindles, augmentation response) evoked by stimulation of thalamic nonspecific, association, and specific nuclei was investigated in chronic experiments on 11 cats before and after successive destruction of the caudate nuclei. After destruction of the caudate nuclei the duration of spindle activity in the frontal cortex and subcortical formations (thalamic nuclei, globus pallidus, putamen) was reduced to only three or four oscillations. In the subcortical nuclei its amplitude fell significantly (by 50±10%); in the cortex the decrease in amplitude was smaller and in some cases was not significant. Different changes were observed in the amplitude of the augmentation response, depending on where it was recorded. In the subcortical formations it was considerably and persistently reduced (by 50±10%); in the cortex these changes were unstable in character. Unilateral destruction of the caudate nucleus inhibited synchronized activity evoked by stimulation of the thalamic nuclei on the side of the operation only. Destruction of the basal ganglia (caudate nucleus, globus pallidus, entopeduncular nucleus, and putamen) did not prevent the appearance of synchronized activity; just as after isolated destruction of the caudate nucleus, after this operation synchronized activity was simply reduced in duration and amplitude. It is suggested that the caudate nucleus exerts an ipsilateral facilitatory influence on the nonspecific system of the thalamus during the development of evoked synchronized activity.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 9, No. 3, pp. 239–248, May–June, 1977.     

Hypothalamic control of visual cortical unit activity in rabbits

During the action of an extracellular polarizing current on neurons of the rabbit visual cortex electrical stimulation was applied to various hypothalamic nuclei (preoptic region, anterior hypothalamic region, lateral hypothalamus, mammillary bodies, and posterior hypothalamic nucleus). Hypothalamic stimulation was found to reduce the mean discharge frequency of most visual cortical neurons tested under conditions of anodal polarization, when the initial level of activity is considerably increased, than to a decrease in activity under conditions of cathodal polarization, when the initial level of activity is considerably reduced. The same tendency toward restoration of the initial (spontaneous) level of unit activity after hypothalamic stimulation was discovered when this level was shifted as a result of stimulation by regular flashes. The greatest effect was observed during stimulation of the preoptic region of the hypothalamus. Stimulation of the posterior hypothalamic nucleus was least effective in this respect.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 9, No. 5, pp. 469–476, September–October, 1977.     

Electrophysiological study of connections between the entorhinal cortex and the neocortex

In acute experiments in rabbits immobilized by d-tubocurarine, stimulation of the entorhinal area with rectangular electric impulses led to the appearance of evoked potentials (EP) with a latent period of 6–12 msec in the occipital, temporal, parietal, and cingular areas of the neocortex. The amplitude of the positive response component was 500 µV, and its duration 25–50 msec. The negative component was not always discernible. When rhythmic stimulation was used, these EPs followed stimulation frequencies not exceeding 20 per sec. Stimulation of the medial parts of the entorhinal area with a frequency of one to three per sec was accompanied by recruitment of the EP in the occipital and temporal neocortex areas. Nembutal depressed the amplitude of the neocortex EP appearing in response to stimulation of the entorhinal cortex. With the aid of double stimulation it could be established that, after conditioning stimulation of the entorhinal area, the positive component of the primary response (PR) evoked by stimulation of the contralateral sciatic nerve in the projection zone of the somatosensory cortex is strengthened during the first 50 msec, and subsequently after 80–120 msec. In these cases, the negative component was depressed. These findings are discussed with a view to the influence of limbic structures on the neocortex.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 2, No. 1, pp. 73–78, January–February, 1970.     

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.     

Responses of limbic cortical neurons to stimulation of splanchnic and sciatic nerves and of the mammillary bodies

Spontaneous and evoked unit activity in the anterior limbic cortex in response to stimulation of the splanchnic and sciatic nerves and of the mammillary region of the hypothalamus were recorded extracellularly in acute experiments on cats. The study of heterogeneous transsynaptic influence on limbic cortical neurons showed that in the presence of effective sensory viscerosomatic convergence, weak convergence of influences from the central hypothalamic and peripheral sources took place. Short-latency responses of limbic cortical neurons to stimulation of the mammillary bodies consisted of orthodromic and antidromic responses, evidence of the existence of short two-way connections between the anterior limbic cortex and mammillary nuclei of the hypothalamus.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 11, No. 5, pp. 419–426, September–October, 1979.     

Changes in the functional characteristics of Clare-Bishop area cells after partial unilateral isolation of the neocortex in cats

Evoked unit activity was investigated bilaterally in neurons of the Clare-Bishop area in cat brain after unilateral severing of the posterior limb of the internal capsule. Cell responses to photic, acoustic, and somatosensory stimuli, also to electrical stimulation of the association areas of the neocortex were investigated. The most rudimentary type of response to a diffuse light flash, electrical stimulation of the forepaw skin, and acoustic stimulation was restored in a proportion of test cells in the operated hemisphere within one week of operating. Sensitivity to visual stimuli increased considerably in cells of the Clare-Bishop area of the intact hemisphere during the first week after the operation. All test cells responded to presentation of light flashes; 80% had receptive fields located to electrical stimulation of the forepaw skin. Seven days after the operation the number of cells responding to photic stimulation fell to 35% and only 17% of cells responded to somatosensory stimuli. This article discusses features of the neuronal compensatory reorganization of the Clare-Bishop area and its role in the recovery of visual function.Institute of Experimental Medicine, Academy of Medical Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 18, No. 2, pp. 180–187, March–April, 1986.     

Projections of the posterior area of the hypothalamus to its medial,anterior, and lateral areas

The effect of stimulation of the lateral and medial supramammillary areas of the posterior hypothalamus on spontaneous single unit activity in the anterior, lateral, medial dorsal, and medial ventral areas of the hypothalamus was investigated in acute experiments on rabbits. Single stimulation of the medial area of the posterior hypothalamus evoked responses of 44% of neurons, whereas stimulation of the lateral area did so in only 35% of all neurons recorded. Repetitive stimulation led to an increase in the number of responding neurons (to 57% during stimulation of the lateral and 74% during stimulation of the medial supramammillary area). In response to repetitive stimulation of the medial supramammillary area, activating influences became predominant in all areas, whereas in response to stimulation of the lateral area, they became predominant in the medial, ventral, and lateral areas. The results are assessed from the standpoint of the role of the posterior hypothalamus in the regulation of adenohypophyseal functions.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 9, No. 4, pp. 377–381, July–August, 1977.     

The effect of electric stimulation of different regions of the cerebral cortex on the alimentary reaction in rabbits]

The influences of different parts of the neocortex on the rabbit alimentary behaviour produced by stimulation of the hypothalamic "alimentary centre" were studied in chronic experiments on rabbits with electrodes implanted in different formations of the limbic system and the midbrain. It has been found that electrical stimulation of the frontal and anterior parietal cortical areas raised the threshold of the evoked alimentary reaction. Inhibitory influences of the frontal areas proved to be stronger and more prolonged than those of the anterior parietal area. Electrical stimulation of the posterior parietal and occipital cortical areas decreased the threshold of the evoked alimentary reaction. Coagulation of the dorsal hippocampus eliminated the inhibitory influences of the neocortex, while coagulation of the mesencephalic reticular formation discontinued the facilitating influences of the neocortex on the alimentary reaction.     

Independent effects of cholinergic and serotonergic lesions on acetylcholine and serotonin release in the neocortex of the rat

Rats received a unilateral lesion of the nucleus basalis magnocellularis (NBM) by infusion of ibotenic acid. In addition, the dorsal raphe nucleus was lesioned by infusion of 5,7-dihydroxytryptamine (5,7-DHT). The release of acetylcholine (ACh), choline, serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) was measured in the frontal neocortex by means of microdialysis. Lesions of the NBM, but not the raphe nucleus, reduced the release of ACh significantly (–47%). The release of 5-HT and 5-HIAA was reduced by raphe lesions (–44% and –79%), but not by NBM lesions. In no case did the combined lesion affect neurotransmitter release more than a single lesion. These results suggest that serotonergic projections from the dorsal raphe nucleus are not involved in tonic inhibition of ACh release in the neocortex.     

Limbico-reticular relations during formation of various motivation responses in rabbits subjected to ethanol administration

Chronic experiments on rabbits with electrodes implanted into different limbic-midbrain structures were made to study the effects of a single intravenous injection of ethanol (0.5 g/kg) on the background EEG during formation of food motivation and avoidance behavior from the criterion of the power of the main EEG rhythms. Intravenous injection of ethanol resulted in an increase in the power of beta-, alpha- and theta-rhythms in the frontal cortex, and in that of alpha- and theta-rhythms in the occipital area of the neocortex. New patterns of the powers of the main EEG rhythms recorded in animals exposed to ethanol during electric stimulation of the lateral and ventromedial hypothalamus, evoking food motivation and avoidance behavior, as well as during electrical stimulation of the dorsal hippocamp and mesencephalic reticular formation that correlate with changes in the functions of the study limbic-mesencephalic structures attest to profound ethanol-induced abnormalities of the central mechanisms of food motivation and avoidance behavior.     

Effect of stimulation of neocortical regions and the subiculum on hippocampal neurons in rabbits

In chronic experiments on rabbits using extracellular recording of unit activity in hippocampal area CA₁ the effects of stimulation of the subiculum, posterior cingulate cortex, and anterior and posterior nonprimary areas of the neocortex were investigated. The effects of such stimulation were compared in the intact and chronically isolated hippocampus. It is concluded from the results that direct two-way connections exist between CA₁ and the subiculum. Polysynaptic influences of the subiculum on CA₁ are realized through the entorhinal cortex, for they are not present in the isolated hippocampus. Influences of the neocortical areas studied on CA₁ are transmitted to some extent through a relay in the subiculum. The entorhinal cortex plays no part in the realization of polysynaptic effects. The effectiveness of these influences increases with removal of the principal hippocampal afferent systems.Institute of Biological Physics, Academy of Sciences of the USSR, Pushchino-on-Oka. Translated from Neirofiziologiya, Vol. 14, No. 3, pp. 315–323, May–June, 1982.     

Effect of peripheral stimulation on neocortical electrical activity in the chronic premesencephalic cat

Chronic experiments on 19 adult cats showed that on the second or third day after premesencephalic section through the brain stem preserving the lemniscal pathways, auditory, olfactory, and cutaneous stimulation evoke diffuse neocortical activation. Although photic stimulation evoked responses in the visual cortex, it could not desynchronize the neocortical activity. It is postulated that diffuse neocortical activation in cats with a complete block of the mesencephalic recticular formation in response to auditory, olfactory, and cutaneous stimulation arises through excitation of the posterior hypothalamus.Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 7, No. 5, pp. 493–499, September–October, 1975.     

Neonatal cerebral cortical lesion abolishes the anxiolytic action of diazepam in adult rats: effects of location and extent of cortical lesion.

In our previous study, diazepam (DZP), a benzodiazepine receptor agonist, failed to suppress foot-shock-elicited ultrasonic vocalizations (USVs) in adult rats that had been neonatally lesioned in the neocortex. Because neonatal lesion of the neocortex did not influence the production of USVs, the presence of an anxiolytic mechanism of DZP is suggested apart from any anxiogenic mechanism in the brain. However, the previous study did not indicate any specific cortical regional lesions that impaired the normal development of the anxiolytic mechanism in the brain. The present study was undertaken in order to examine whether neonatal lesion of the neocortex, smaller and more localized than that in the previous study, abolishes the anxiolytic effect of DZP on foot-shock-elicited and air-puff-elicited USVs. A neonatal lesion about 2 mm diameter was made in the unilateral frontal cortex frontal to the hindlimb area or in the occipital cortex caudal to the hindlimb area. The attenuating effect of DZP on the USVs elicited by both aversive stimuli was found to be abolished only in the frontal cortex-lesioned rats. This finding indicates that the frontal cortex is likely to be specifically involved in the normal development of the benzodiazepine-anxiolytic mechanism in the brain.