Effect of vestibular,somatic, and autonomic afferent impulsation on vestibular nuclear unit activity in cats

Single unit responses in nuclei of the vestibular complex to stimulation of the labyrinths and of proprioceptive and autonomic afferents were investigated. Different types of unit responses were obtained to stimulation, including evoked activity consisting of a group of action potentials followed by inhibition of the spike discharge. Unit activity in the vestibular nuclei was shown to depend on extralabyrinthine stimulation. In response to adequate stimulation of the labyrinths by tilting the head, the role of receptors of muscles and joints in the neck was distinguished. The question of the somatotopic organization of the vestibular nuclei and convergence of various afferent flows on neurons giving rise to the vestibulospinal tract is discussed.Institute of Medico-Biological Problems, Ministry of Health of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 8, No. 5, pp. 507–513, September–October, 1976.     

Cortico-pyramidal and cortico-extrapyramidal synaptic influences on lumbar motoneurons in monkeys

Postsynaptic potentials evoked by stimulation of the motor cortex or pyramids before and after acute pyramidotomy were investigated in the lumbar motoneurons of monkeys. In response to activation of fibers of the pyramidal tract monosynaptic EPSPs predominated in motoneurons innervating the distal muscles of the hind limbs. Monosynaptic EPSPs in the motoneurons of the distal muscles had a significantly higher amplitude and could be evoked by weaker stimuli than EPSPs in the motoneurons of the proximal muscles. Cortico-motoneuronal EPSPs in the motoneurons of the distal muscles had a less marked frequency potentiation than EPSPs with monosynaptic segmental delay in the motoneurons of the proximal muscles. Cortico-extrapyramidal synaptic responses appeared in the pyramidotomized monkeys during intensive repetitive stimulation of the motor cortex in motoneurons of both distal and proximal muscles. These effects, transmitted by descending projections of the brain stem, may be responsible for the partial preservation of cortical motor control after pyramidotomy.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 4, No. 6, pp. 587–596, November–December, 1972.     

Role of dominant motivation in producing the effects of electric stimulation of hypothalamo-limbic structures

The experiments were made on cats with electrodes chronically implanted in the hypothalamus and the amygdala. The effects of electrical stimulation of the points from which the food reactions were initially evoked, were transformed into an avoidance reaction, if stimulation was applied in surroundings where the animals had previously received pain stimuli. Defensive reactions to stimulation of the hypothalamus and amygdala changed to alimentary reactions if the same stimulation was presented to hungry cats in conditions of repetitive feeding. A conclusion has been drawn that the elements of the hypothalamo-limbic structures have plastic properties and may be involved in different forms of behaviour, depending on current motivation and learning.     

The influence of target sex and dominance on evoked attack in Rhesus monkeys

Attack behaviors were elicited by the electrical stimulation of the hypothalamus of freely moving male rhesus monkeys. The influence of the sex and dominance status of target animals on the evoked response was measured. Animals offered as targets were dominant males and females and subordinate males and and females. Males were attacked more often than females and subordinate targets of either sex were attacked more often than dominant targets. A comparison was made between spontaneous and evoked attack behavior.     

Effect of injury to the lateral reticular nucleus and nuclei of the inferior olive on electrical responses of the cerebellar cortex evoked by vagus nerve stimulation in cats

The role of the lateral reticular nucleus and nuclei of the inferior olive in the formation of cerebellar cortical evoked potentials in response to vagus nerve stimulation was determined in experiments on 28 cats anesthetized with chloralose and pentobarbital. After electrolytic destruction of the lateral reticular nucleus, in response to vagus nerve stimulation, especially ipsilateral, lengthening of the latent period and a decrease in amplitude of evoked potentials were observed; after bilateral destruction of this nucleus, evoked potentials could be completely suppressed. It is concluded that the lateral reticular nucleus relays interoceptive impulses in the vagus nerve system on to the cerebellar cortex. Additional evidence was given by the appearance of spike responses of Purkinje cells, in the form of mainly simple discharges, to stimulation of the vagus nerve. After destruction of the nuclei of the inferior olive, the latent period and the number of components of evoked potentials in response to vagus nerve stimulation remained unchanged but their amplitude was reduced. The role of the nuclei of the inferior olive as a regulator of the intensity of the flow of interoceptive impulses to the cerebellum is discussed.N. I. Pirogov Medical Institute, Vinnitsa. Translated from Neirofiziologiya, Vol. 9, No. 3, pp. 290–299, May–June, 1977.     

Reactions of neurons of orbitofrontal cortex to stimulation of limbic system formations

The reactions of 164 neurons of the orbitofrontal cortex (OFC) to stimulation of the mediodorsal nucleus of the thalamus (MD), the amygdaloid complex, and various sections of the hypothalamus, were investigated in acute experiments on cats. Stimulation of the MD led to the development in OFC neurons of reactions with a short (sometimes less than 6 msec) and stable latent period. Similar reactions were observed upon stimulation of the lateral amygdaloid nuclei. Stimulation of the basal and central nuclei of the amygdala evoked synchronization of the discharges in OFC neurons. Stable responses of OFC neurons developed from nuclei of the hypothalamus only in the lateral region. Stimulation of the other nuclei of the hypothalamus was accompanied by irregular responses or synchronization of the discharges. In an analysis of the material obtained, the functional characteristics of the connections between the structures investigated and OFC neurons were examined.State Medical Institute, Kemerovo. Translated from Neirofiziologiya, Vol. 3, No. 5, pp. 484–490, September–October, 1971.     

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.     

Conditioned reflex reproduction of evoked potentials during reinforcement by electrostimulation of the hypothalamus]

Conditioned evoked potentials to stimulation of a limb, a light flash or a short tone were studied on rats in acute experiments with nembutal anaesthesia and in chronic experiments. Electrical stimulation of the hypothalamus was used as reinforcement. Following the pairings of conditioned and hypothalamic stimulation, the appearance of conditioned EP was recorded, as manifest in the period of the previously applied unconditioned signal after its omission. Their emergence was facilitated after high-frequency stimulation of the hypothalamus or administration of galantamine, an anticholinesteraze drug. Coagulation of the hypothalamus did not prevent any manifestation of conditioned evoked potentials.     

Participation of adrenal hormones in the genesis of arterial hypertension of hypothalamic origin]

Continuous many-hour stimulation of the hypothalamic negative emotiogenic centres (ventromedial nuclei) evoked a stable arterial hypertension with a peculiar phasic dynamics of the adrenal secretory activity in waking immobilized rabbits. Bilateral extirpation of the adrenal glands decreased the initial level of the average arterial pressure, inhibiting development of stable arterial hypertension. Many-hour stimulation of the mentioned structures also produced stable arterial hypertension in adrenalectomized rabbits if preceded by the administration of hydrocortisone together with adrenaline. Against the background of separate administration of hydrocortisone and adrenaline to adrenalectomized rabbits, many-hour stimulation of the ventromedial hypothalamus evoked a short-term rise in the arterial pressure. A conclusion was drawn that activation of hormones of the adrenal cortical and medullary layers played an important part in the formation of stable arterial hypertension in rabbits under continuous many-hour stimulation of the hypothalamic negative emotiogenic centres.     

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.     

Analysis of the effect of increasing electrodermal stimulation on the somatovegetative reactions evoked by stimulation of the ventromedial hypothalamus

The influence of increasing electrodermal stimulation (EDS) on the dynamics of the somatovegetative reactions evoked by electrical stimulation of negative emotiogenic regions of the hypothalamus was studied. EDS produced a blocking effect on the somatovegetative reactions evoked by stimulation of the ventromedial hypothalamus (VMH). Pretreatment with naloxone prevented the effects of EDS. Injection of beta-endorphine in a dose of 10 micrograms to the lateral ventricules of the animal brain also blocked the somatovegetative reactions during VMH stimulation. Injection of beta-endorphine in doses of 50-100 micrograms enhanced and prolonged the somatovegetative reactions evoked by VMH stimulation. Elevated arterial blood pressure, pronounced bradycardia, extrasystoles, muscle tremor, and pathologic respiration were recorded. These disorders were completely reversed by EDS. It is assumed that both opiate peptides and their receptors are involved in the mechanism of the somatovegetative reactions evoked by VMH stimulation, experiencing the influence of EDS.     

Structural-functional connections of the lemniscus system with the caudate nucleus in the cat

Afferent projections were studied of nuclei of the spinal cord dorsal columns to the caudate nuclei. Evoked potentials (EPs) were recorded in the caudate nuclei and the nuclei of dorsal columns of the spinal cord to stimulation of the forelimb against the background and after unilateral elimination of the medial lemniscus. After the section, the EPs in the recorded nuclei sharply intensified in response to stimulation of the forelimb, ipsilateral to the section. Degenerative changes were also shown by electron microscopy in axonal terminals in the caudate nuclei at the operated side. Conclusion is drawn that the caudate nuclei receive direct connections from the contralateral nuclei of the spinal cord dorsal columns, which probably, conduct mainly kinesthetic afferent influences.     

Adrenomedullary pressor responses to stimulation of the rostral hypothalamus in the rat: influence of adrenaline-induced vasodilation and reflex cardioinhibition

Electrical stimulation (100 Hz, 1 ms, 150 microA, 10 s) of the anterior hypothalamus in chloralose-anesthetized rats evoked a biphasic pressor response consisting of an initial sharp rise in arterial pressure at the onset of stimulation, followed by a second elevation after cessation of the stimulus. This response was accompanied by an increase in plasma noradrenaline and adrenaline levels. Peripheral sympathectomy with guanethidine selectively abolished the primary phase of the biphasic pressor response, while bilateral removal of the adrenal medulla eliminated only the secondary component. After alpha-adrenergic blockade with phentolamine, the primary phase of the stimulation-induced response was reduced while the secondary pressor component was blocked and replaced by a significant hypotension. The intravenous administration of sotalol enhanced the secondary pressor component without affecting the stimulation-induced plasma noradrenaline and adrenaline responses. After treatment with atropine, the secondary pressor effect was also potentiated, as the reflex bradycardia normally associated with the response was eliminated. A subsequent administration of sotalol in these rats further potentiated the secondary pressor component to stimulation. In rats treated with atropine and sotalol, the sympathetic vasomotor and the adrenomedullary pressor responses could be dissociated according to thresholds and stimulus frequency or current-response characteristics. The results suggest that in intact rats, adrenaline-induced vasodilation and reflex cardiac inhibition contribute to either reduce or mask the adrenomedullary component of the biphasic pressor response evoked by stimulation of the anterior hypothalamus. The study also raises the hypothesis of a dual regulation of both components of the sympathetic system in the anterior hypothalamic region.     

Hysteresis properties of movement in elbow joint of unanesthetized cats when antagonistic muscles are activated using different methods

Flexing and extending movements of the elbow joint were studied in unanesthetized cats. These movements were evoked by intracortical microstimulation and by vibration of the forepaw. After the animals were anesthetized the same movements were studied in response to direct stimulation of the antagonistic muscles. Interaction of the hysteresis effects in the antagonistic muscles under conditions of cortical-evoked movements in response to stimulation of two points of the cortex, one of which evoked flexion, and the other extension of the elbow joint, was studied using external local disturbance. Coactivation of the antagonists was shown to increase both the joint stiffness and the ambiguity of the equilibrium of the joint angle. This ambiguity was expressed in both the antagonistic actuating disturbances as well as in the change of the sequence for activating the antagonistic muscles. Comparison of the cortical-evoked movements and movements evoked by vibrating the forepaw when tested with an external load disturbance showed that with intracortical microstimulation the myotatic reflexes in the activated muscle are suppressed, but when vibration is used they are well defined in both antagonistic muscles. At the same time, in spite of the significantly different pathways for activating spinal neurons, the ambiguity effects displayed when determining the equilibrium of the joint angle were similar in both cases.A. A. Bogomolets Physiology Institute, Ukrainian Academy of Sciences, Kiev. Translated from Neirofiziologiya, Vol. 24, No. 3, pp. 322–330, May–June, 1991.     

Role of the hypothalamus in regulating liver circulation

In acute experiments on nembutal anesthetized dogs stimulation of anterior hypothalamus elicited changes in the hepatic artery blood flow, which followed those of arterial pressure; the vascular resistance remaining unchanged. The stimulation of medial and posterior hypothalamus led to decrease in flow and increase in the resistance of the hepatic artery. In most cases of hypothalamic stimulation the portal blood flow diminished, portal pressure and vascular resistance increased. The opposite reactions were observed during stimulation of sympathoinhibitory area, paraventricular and lateral hypothalamic nuclei. The conclusion is made that the hypothalamus participates in integrative and differential control of the hepatic circulation.     

Effect of chronic stimulation of the negative and positive emotionogenic centers of the hypothalamus on development of cardiac arrhythmias]

Chronic experiments were conducted on 46 rabbits; a study was made of the changes in cardiac activity arising in prolonged (up to 1--2 weeks) electric stimulation of the ventro-median nuclei of the hypothalamus. Disturbances of the cardiac rhythm in the form of tachycardia, atrial flutter and fibrillation, ventricular extrasystole and paroxysmal ventricular tachysystole occurred mostly during the first days of stimulation and ceased after inderal infusion. Functional "weakness" of the cardiac pacemakers was revealed in the animals subjected to 1--2-week stimulation of the ventromedian nuclei. This was indicated by the post-stimulation suppression of the pacemaker automaticity and the appearance of Liciani's periods. Disturbances of the cardiac rhythm originating in stimulation of the ventromedian nuclei ceased in stimulation of the lateral hypothalamic field.     

Inhibition of jaw opening reflexes by stimulation of the central gray matter and raphe nuclei in cats

The effect of stimulation of the mesencephalic central gray matter and raphe nuclei on jaw opening reflexes evoked by excitation of high-threshold (dental pulp) and low-threshold (A-alpha) fibers of the infraorbital nerve afferents was studied in cats anesthetized with chloralose and pentobarbital. The jaw opening reflex evoked by stimulation of the dental pulp was shown to be effectively suppressed by conditioning stimulation of the central gray matter and raphe nuclei. The reflex evoked by stimulation of low-threshold infraorbital nerve afferents also was depressed (but less deeply and for a shorter period than the reflex evoked by stimulation of the dental pulp) during stimulation of the raphe nuclei and caudal zone of the central gray matter, but was unchanged after stimulation of the points located in the rostral zone of the central gray matter. Application of single stimuli or bursts of five stimuli with a frequency of 100 Hz had no effect on the reflexes studied. Short-term stimulation with a burst of 10–20 stimuli with a following frequency of 200–400 Hz led to inhibition of the reflexes, which lasted 450–1000 msec. Long-term stimulation of the central gray matter and raphe nuclei for 30 sec with a frequency of 50 Hz caused inhibition of jaw opening reflexes evoked by stimulation of both high- and low-threshold afferents for 60 min. Impulses from the central gray matter and raphe nuclei thus have a mainly inhibitory action on the jaw opening reflex evoked by stimulation of high-threshold afferents, but they act less effectively on the reflex evoked by stimulation of low-thres-hold afferents. The duration of inhibition depends essentially on the parameters of stimulation.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 3, pp. 374–387, May–June, 1984.     

Synaptic reactions of sensomotor cortex neurons to stimulation of emotionally significant brain structures

The study deals with synaptic and spike responses of neurones in the rat sensorimotor cortex to stimulation of the lateral and medial hypothalamus, locus coeruleus and raphe nuclei. The activity of 57 neurones was recorded, 41 of them intracellularly and quasi-intracellularly, in response to the stimulation of sites in these structures, which were previously identified as "emotionally/ significant. No considerable differences in the effects of the stimulation of different "emotiogenic" zones were found. The stimulation parameters, differing from the "behavioural" ones by a greater strength, elicited in the majority of neurones clear post-synaptic responses, often in the form of EPSP-IPSP. Latencies of the responses varied from 3 to 80 msec. The most stable and pronounced responses were obtained to the stimulation of the lateral hypothalamus. No significant correlations of the latencies of the responses to the stimulation of different "emotiogenic" structures were found.     

Electrophysiologic study of hippocampo-hypothalamic connections in rabbits

Using the evoked potentials (EP) studies have been made on functional connections of different fields (CA1, CA3) of the dorsal hippocamp with phylogenetically different parts of the hypothalamus in rabbits. It was shown that during stimulation of both the field CA1 and the field CA3 of the hippocamp, the EP are widely present in nuclear structures of the posterior hypothalamus (supramammilary area, the posterior hypothalamic area, mammilary bodies). In the anterior hypothalamus (area preoptic medialis), the EP were recorded only during stimulation of the field CA1 in the dorsal hippocamp.