Corticofugal influences on the neurons of different regions of the hypothalamus

Responses of the neurons of the lateral and ventromedial hypothalamic regions (HL andHvm, respectively), as well as of the area of the dorsal hypothalamus (aHd) and the projection region of the medial forelimb bundle (MFB), evoked by stimulation of the proreal cortex (field 8), cingular cortex (field 24), pyriform lobula (periamigdalar cortex), and hippocampus (CA3) were studied in acute experiments on cats under ketamine anesthesia. Distributions of the latent periods of the responses recorded from hypothalamic neurons at stimulation of the above cortical structures were analyzed. The responses were classified into primary excitatory and primary inhibitory. Stimulation of the proreal gyrus evoked four times more excitatory responses than inhibitory responses. With stimulation of the cingular gyrus, the ratio of excitatory/inhibitory responses was 1.5∶1. Stimulation of the pyriform cortex evoked activatory and inhibitory responses with a similar probability. With hippocampal stimulation, inhibitory responses appeared two times more frequently than excitatory reactions. The hypothalamus was found to be a zone of wide convergence: one-half of all responding neurons in theHL andHvm responded to stimulations of two or more tested cortical zones. In 26% of the cells, only excitatory convergence was observed, while in 10% only inhibitory convergence was found; 21% of the cells revealed mixed convergence.     

Electrophysiological analysis of cortico-tectal connections in the turtle

Two types of evoked potentials are recorded in the tectum mesencephali in response to electrical stimulation of the forebrain surface of the turtleEmys orbicularis. The results of a layer-by-layer analysis show that evoked potentials of type I in response to stimulation of the hippocampal and piriform cortex are generated outside the tectum. Evoked potentials of type II, consisting of two surface-negative components, are recorded in the tectum in response to stimulation of the rostro-central surface of the forebrain. The first component appeared after a latent period of 20 msec and lasted 40–60 msec; the second component appeared after 80–100 msec and lasted 100–300 msec. Layer-by-layer and pharmacological analysis showed that the first component of the type II evoked potential is generated in the tegmental structures of the mesencephalon, whereas the second (long-latency) is generated in the tectum. The tectal origin of the second component is confirmed by its interaction with the tectal response to photic stimulation or to electrical stimulation of the optic nerve, evidence that these evoked potentials are generated by common structures. The efferent pathway from the dorsal cortex to the primary visual center is unilateral and has features of polysynaptic projections (long latent period, low lability).     

Corticofugal influences on the motoneurons of the trigeminal nucleus

We studied the postsynaptic potentials evoked from 76 trigeminal motoneurons by stimulation of the motor (MI) and somatosensory (SI) cortex in the ipsilateral and contralateral hemispheres of the cat. Stimulation of these cortical regions evoked primarily inhibitory postsynaptic potentials (PSP) in the motoneuron of the masseter muscle, but we also observed excitatory PSP and mixed reactions of the EPSP/IPSP type. The average IPSP latent period for the motoneurons of the masseter on stimulation of the ipsilateral cortex was 6.1±0.3 msec, while that on stimulation of the contralateral cortex was 5.2±0.4 msec; the corresponding figures for the EPSP were 7.6±0.5 and 4.5±0.3 msec respectively. Corticofugal impulses evoked only EPSP and action potentials in the motoneurons of the digastric muscle (m. digastricus). The latent period of the EPSP was 7.6 msec when evoked by afferent impulses from the ipsilateral cortex and 5.4 msec when evoked by pulses from the contralateral cortex. The duration of the PSP ranged from 25 to 30 msec. Postsynaptic potentials developed in the motoneurons studied when the cortex was stimulated with a single stimulus. An increase in the number of stimuli in the series led to a rise in the PSP amplitude and a reduction in the latent periods. When the cortex was stimulated with a series of pulses (lasting 1.0 msec), the IPSP were prolonged by appearance of a late slow component. We have hypothesized that activation of the trigeminal motoneurons by corticofugal impulsation is effected through a polysynaptic pathway; each functional group of motoneurons is activated in the same manner by the ipsilateral and contralateral cortex. The excitation of the digastric motoneurons and inhibition of the masseter motoneurons indicates reciprocal cortical control of their activity.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 3, No. 5, pp. 512–519, September–October, 1971.     

Features of evoked potentials in the cerebellar cortex of rabbits

We investigated evoked responses of the cerebellar cortex of rabbits under Nembutal or chloralose anesthesia to stimulation of the sciatic, brachial, and vagus nerves. The parameters of evoked potentials (E Ps), together with features of their distribution throughout the cerebellar cortex, enabled us to divide them provisionally into three types. Evoked potentials of the first type have a latent period of 5–10 msec and a two-phase or more complex shape. Evoked potentials of the second type have a latent period of 10–23 msec and include from one to four components. Evoked potentials of the third type are discharges with long latent periods (20–50 msec) and consist of a series of slow sinusoidal oscillations. Appearance of an initial electronegative component is characteristic of EPs of the cerebellar cortex of rabbits, especially those of the second and third types. Evoked potentials of the first type are local.N. I. Pirogov Vinnitsa Medical Institute. Translated from Neirofiziologiya, Vol. 1, No. 1, pp. 73–80, July–August, 1969.     

Comparative electrophysiological characteristics of afferent representation in the cortical and striatal divisions of the turtle forebrain

In experiments on immobilized, lightly anesthetized turtles the presence of visual and somatic representation was established in the subcortical striatal division of the forebrain — the pallial thickening, the dorsal ventricular ridge, and the putamen. In their physiological characteristics they are similar to the corresponding representation in the general cortex. The absence of significant differences between the latent periods of cortical and striatal evoked potentials to flashes and to stimulation of the dorsal thalamus indicates that visual projection fibers (from the lateral geniculate body) terminate at both cortical and striatal levels. Differences in the distribution of latent periods of unit responses in the cortex to visual and thalamic stimulation are due to the presence of a rotundo-telencephalic visual channel, with direct connections with the striatal and polysynaptic connections with the general cortex, as well as the geniculo-telencephalic tract. Considerable differences between the latent periods of the evoked potentials and also between unit responses to electrodermal stimulation in the cortical and striatal structures indicate that somatic projection fibers relay in the striatum on their path to the general cortex. Consequently, the somatosensory system of turtles is less corticalized than the visual system. Comparison of the results described with those obtained by workers studying other vertebrates suggests that the afferent supply of the striatum may be reorganized in the transition from premammals to mammals.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 7, No. 2, pp. 184–193, March–April, 1973.     

Development of the hypothalamic-cortical interrelations in the ontogeny of the cat

Under chloralose narcosis, employing the evoked potentials method, studies have been made on the projection of the posterior hypothalamus to the frontal cortex in 1-30 days old kittens. The animals were divided into 3 age groups: 1-9, 10-19 and 20-30 days. Studies of the EPs in different points of pericruciate zone showed that these potentials are observed in all the investigated points from the first days of postnatal life. The latent period of responses in the youngest animals varied from 40 to 80 ms, exhibiting insignificant fluctuations depending on the cortical zone investigated. From the very beginning of postnatal life, in the same cortical zone the EPs may be observed in response to stimulation of the ischiadic nerve as well. In older animals, the latent period of the EPs decreases in all the points, the decrease being most significant near the crucial fissure. To the 30th day of postnatal life, the EPs in this zone with respect to their latency and configuration became quite similar to those in adult animals. In the third age period, the latency varies from 6 to 10 ms in the focus of maximum activity; with the removal of the recording electrode from this zone the latent period of the hypothalamo-cortical responses increases up to 30-40 ms. Overlapping of the EPs in response to central and peripheral stimulation was observed at all age periods.     

The neuronal organization of the limbic (cingulo-)-visceral reflex arc

The paper summarizes new electrophysiological data concerning the structural-functional organization of the limbic cortex and role of the rostral limbic region of visceral functions. Here are presented the results of a series of electrophysiological investigation of the focus of localization in the supracallosal (area 24) and infracallosal (area 25) part of the anterior cingulate gyrus of evoked potentials of maximal amplitude and minimal latent period to stimulation of pelvic, splanchnic and sciatic nerves. It was shown that evoked potentials of maximal amplitude and minimal latent periods to stimulation of viscero-somatic nerves are recorded in the supragenual area 24 in comparison with the infragenual area 25 of the anterior limbic cortex. In a series of microelectrophysiological studies of reactions of neurons of area 24 and 25 it was established that the reactivity of neurons of area 24 is higher than that of area 25. All these data indicate to the leading role of area 24 in reception and treatment of viscero-somatic afferent signals. In series of experiments it was shown that the focus of exciting neurons, forming the descending singular-autonomic discharge is localized in the infragenual area 25 of anterior limbic cortex. In a study of the comparative characteristics of sympathetic responses in lumbar white communicating rami and parasympathetic responses in pelvic nerve it was shown that evoked potentials in pelvic nerve and white rami had the lowest threshold and shorter latency in case of stimulation of area 25. Study of characteristics of influence of dorsal (area 24) and ventral (area 25) regions of rostral limbic cortex on bioelectrical activity of two postganglionic sympathetic nerves-inferior cardiac and vertebral branches of stellate ganglion, innervating coronary vessels and vessels of anterior extremities correspondingly, showed that stimulation of ventral area 25 evoked increase of electrical activity of the two sympathetic nerves and reliable increase of systemic arterial pressure, while stimulation of dorsal area 24 evoked decrease of tonic activity of the two sympathetic nerves and reliable decrease of systemic arterial pressure. In the paper are presented also the results of microelectrophysiological investigation of peculiarities of reactions of inspiratory and expiratory neurons of bulbar respiratory center to high frequency stimulation of area 24 and 25--in case of stimulation of dorsal area 24 the prevailing effect is suppression of spike activity of neurons, of stimulation of ventral, infragenual area 25 the prevailing influence is excitatory. In another series of microelectrophysiological experiments it was shown downward blocking inhibitory influence of dorsal supragenual area 24 of anterior limbic cortex on activity of vagal viscerosensory neurons of bulbar solitary tract nucleus. It is concluded that the strictly connected one another areas 24 and 25 of limbic cortex are functionally differentiated: the infra-limbic cortex is mainly a viscero-motor cortex, while the prelimbic area 24 plays a leading role in reception and treatment of viscero-somatic afferent information.     

Effect of positive and negative emotional states on the electrical activity of the auditory cortex in rabbit ontogeny

It has been shown that in all age groups of animals, self-stimulation of the hypothalamus is accompanied with the decrease in the latent period and the increase in the amplitude of the evoked potential (EP) in the auditory cortex. During negative stimulation, the increase in temporal parameters of the response takes place together with the decrease in the amplitude of the EP and the onset of secondary waves. Significant age changes were revealed in the recovery of the initial pattern of the EP after cessation of stimulation of emotiogenic zones. The recovery of the EP after stimulation of the "reward" zone in younger rabbits occurs 4 times faster than in adult animals, whereas in the former the recovery period of the EP after stimulation of the "punishment" zone is significantly longer.     

Analysis of long-latency components of field potentials evoked by stimulation of the cerebral cortex and nerves in the cerebellar paramedian lobule

Field potentials evoked in the graunular layer of the cerebellar paramedian lobule of unanesthetized cats in response to stimulation of the sensomotor cortex and limb nerves contained slow negative waves, appearing after a long latent period, which were generated by granule cells. In the case of nerve stimulation this component was recorded both inside and outside the projection zone of the corresponding limb. Cortical stimulation by single stimuli or series of stimuli not more than 1.8–2.5 times above threshold strength led to the appearance of evoked potentials only inside the corresponding projection zone. The long-latency component of field potentials evoked by cerebral stimulation followed high frequencies of repetitive stimulation and was less sensitive to the action of barbital anesthesia than the analogous component of potentials evoked by nerve stimulation. In the case of combined cerebral and nerve stimulation the long-latency components underwent summation. It is concluded that mossy fibers of slowly-conducting spino- and cerebrocerebellar tracts innervate different granule cells in the cerebellar cortex.Institute of Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 14, No. 4, pp. 379–385, July–August, 1982.     

Hypothalamic evoked potentials to vagus and sciatic nerve stimulation

Hypothalamic evoked potentials to stimulation of the cervical portion of the vagus nerve and the sciatic nerve were recorded in experiments on cats anesthetized with chloralose and immobilized with succinylcholine. When both monopolar and bipolar recording techniques were used the focus of maximal activity of both "visceral" and "somatic" evoked potentials was located in the supramammillary and posterolateral region of the hypothalamus. Responses in the tuberal and anterior hypothalamus occurred in most experiments after a longer latent period, their amplitude was lower, and they were less stable. Evoked potentials in the focus of maximal activity of the posterior hypothalamus are similar in all parameters to responses of the mesencephalic reticular formation. Evoked potentials to stimulation of the visceral nerve have a higher threshold of generation and a lower amplitude than the "somatic" responses and they are inhibited more strongly when the frequency of stimulation is increased. Evoked potentials arising in the hypothalamus in response to stimulation of the vagus and sciatic nerves are regarded as nonspecific responses of reticular type.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 5, No. 3, pp. 253–260, May–June, 1973.     

Evoked potentials to electrical stimulation of the facial nerve in the carp tectum mesencephali

Tectal evoked potentials to stimulation of the facial nerve, containing afferent fibers of nonolfactory chemoreception, in the carp are positive evoked potentials with a latent period of 5 to 25 msec which show no phase shift as the microelectrode is advanced to a depth of 600 µ. Depending on the amplitude and latency of evoked potentials seven active zones differing in one or both parameters were distinguished in the ipsilateral tectum mesencephali. The role of impulses from the medulla in the mechanism of tectal evoked potentials to facial nerve stimulation is proved by differences in latent periods and disappearance of the tectal response (although it is preserved in the primary center) after severance of connections between the two parts of the brain. Descending influences from the tectum on the primary center were found: its extirpation disturbs evoked potential generation in several parts of the medullla, so that they either disappear completely or their parameters are modified.A. A. Zhdanov State University, Leningrad. Translated from Neirofiziologiya, Vol. 8, No. 1, pp. 39–46, January–February, 1976.     

Postsynaptic potentials of neck muscle motoneurons evoked by horizontal semicircular canal stimulation in cats

Postsynaptic potentials evoked by stimulation of ipsilateral and contralateral horizontal semicircular canals in motoneurons of muscles tilting and turning the head were investigated in acute experiments on cats anesthetized with chloralose and pentobarbital. Stimulation of the ipsilateral canal evoked EPSPs with latent periods varying from 1.8 to 10.0 msec in 25 of these motoneurons and IPSPs with latent periods varying from 1.9 to 3.9 msec in 10 of them. Calculation of the impulse conduction time from the ipsilateral semicircular canal through Deiters' nucleus to the cervical motoneurons indicates that EPSPs with latent periods of under 3.8 msec may be regarded as disynaptic, and those with latent periods of over 3.8 msec as polysynaptic. Stimulation of the contralateral canal evoked EPSPs with latent periods varying from 1.8 to 6.0 msec in 19 motoneurons and IPSPs with latent periods varying from 3.2 to 3.9 msec in two cells. The possible pathways of transmission of these influences and their functional role are discussed.     

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.     

Unit responses in area 5b of the suprasylvian gyrus to stimulation of the posterior lateral thalmamic nucleus

In response to stimulation of the posterior lateral nucleus in unanesthetized cats immobilized with D-tubocurarine an evoked potential consisting of three components with a latent period of 3–5 msec appeared in area 5b of the suprasylvian gyrus. All three components were reversed at about the same depth in the cortex (1500–1600 µ). Reversal of the potential shows that it is generated in that area by neurons evidently located in deeper layers of the cortex and is not conducted to it physically from other regions. Responses of 53 spontaneously active neurons in the same area of the cortex to stimulation of the posterior lateral nucleus were investigated. A characteristic feature of these reponses was that inhibition occurred nearly all of them. In 22 neurons the responses began with inhibition, which lasted from 30 to 400 msec. In 30 neurons inhibition appeared immediately after excitation while one neuron responded by excitation alone. The latent periods of the excitatory responses varied from 3 to 28 msec. The short latent period of the evoked potentials and of some single units responses (3–6 msec) confirms morphological evidence of direct connections between the posterior lateral nucleus and area 5b of the suprasylvian gyrus. Repetitive stimulation of that nucleus led to strengthening of both excitation and inhibition. Influences of the posterior lateral nucleus were opposite to those of the specific nuclei: the posterior ventrolateral nucleus and the lateral and medial geniculate bodies. Stimulation of the nonspecific reticular nucleus, however, evoked discharges from neurons like those produced by stimulation of the posterior lateral nucleus.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 5, No. 5, pp. 502–509, September–October, 1973.     

Change in the evoked potentials of the brain exposed to a constant magnetic field]

The influence of the constant magnetic field (CMF) upon the cerebral and cerebellar cortex potentials evoked by the sciatic stimulation was studied in rats. During the exposure to the CMF there occurred an increase of the evoked potentials in amplitude and the appearance of additional waves in their structure. The effect was enhanced with increase in the intensity of magnetic field within the range of 500-4000 oe.     

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.     

Investigation of pallidofugal influences on hypothalamic activity

In chronic experiments on nine cats electrical stimulation of the posterior zones of the lateral hypothalamus led to reproduction of a conditioned food-getting reflex produced previously in response to clicks. During stimulation of the globus pallidus a food-getting reflex also appeared in 3 of 10 zones studied, but it did so only irregularly. In response to combined stimulation of the hypothalamus and these three zones of the globus pallidus facilitation of this reflex was observed: its intensity was increased and its latent period shortened. Stimulation of other areas of the globus pallidus inhibited the food getting reflex of hypothalamic origin on account of the intensification of purposeless motor responses. Stimulation of the globus pallidus evoked desynchronization of spontaneous hypothalamic electrical activity. After bilateral electrolytic destruction of the globus pallidus and its principal efferent pathway (the ansa lenticularis) no conditioned food-getting reflex was reproduced during hypothalamic stimulation. After pallidectomy the amplitude of the spontaneous waves and evoked potentials was reduced by a statistically significant degree in the hypothalamic zones tested. The results are evidence of the existence of regulatory functional influences of the globus pallidus on the lateral hypothalamus.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 6, No. 6, pp. 592–601, November–December, 1974.     

Vestibular projections in the cat temporal cortex

Boundaries of vestibular projections in the temporal cortex during stimulation of the vestibular nerve were studied in cats anesthetized with pentobarbital and chloralose or chloralose alone. The caudal boundary of the vestibular zone was shown to run along the anterior ectosylvian gyrus. A focus of evoked activity was found in the suprasylvian sulcus or 1–2 mm rostrally to it. All short-latency evoked potentials recorded during vestibular nerve stimulation in the temporal region caudally to the zone mentioned above were connected with the spread of current to auditory structures. To verify the extent of spread of the stimulating current, focal potentials were recorded in the vestibular and superior olivary groups of nuclei. Special experiments were carried out to study the topography of these potentials at the level of bulbar structures during stimulation of vestibular and auditory nerves. According to the results, there is no second vestibular area in the temporal cortex in cats. Vestibular afferentation is projected mainly into the contralateral hemisphere, and the response latency is 5.2±0.7 msec. The ipsilateral evoked potentials had a long latent period (8.4±1.3 msec), and their amplitude depended on the type of anesthesia; it was accordingly postulated that additional synaptic relays exist in this vestibulocortical pathway.     

Excitation of accessory motoneurons by stimulation of Deiters' nucleus in the cat

Acute experiments on cats under chloralose-pentobarbital anesthesia showed that application of single stimuli to Deiters' nucleus evoked monosynaptic EPSPs in motoneurons of the accessory nucleus. Latent periods of EPSPs ranged from 1.3 to 2.3 msec (mean 1.8±0.3 msec), their rise time was 0.5–1.0 msec, and their duration 7–10 msec. During repetitive stimulation the EPSPs were weakly potentiated, but with an increase in the strength of stimulation applied to Deiters' nucleus they readily changed into action potentials. In some motoneurons polysynaptic EPSPs with latent periods of the order of 6.0 msec appeared on the descending phase of these EPSPs.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 5, pp. 515–519, September–October, 1981.     

Changes in the arterial pressure and evoked potential in the sensorimotor cortex induced by nalorphine injected in the hypothalamus during painful electric shock in rabbits

During the hypotensive phase of electronocuous shock in rabbits, injection of nalorphine to the hypothalamus provoked elevation in the blood pressure (BP), recovery of the evoked potential (EP) of the sensorimotor brain cortex in response to electrodermal stimulation (EDS) of the hind limb. Injection of the drug to the central gray of the midbrain resulted in an insignificant short-term elevation of the BP followed by its drop. It is concluded that the endogenous opioid system of the hypothalamus is of importance in the genesis of the hypotensive response and suppression of the EP of the rabbit sensorimotor brain cortex in response to EDS during electronocuous shock.