Afferent connections of cat facial nucleus; a study using retrograde axonal transport of horseradish peroxidase

Neuronal populations in the brainstem and spinal cord — the sources of fiber pathways to the facial nucleus — were investigated in adult cats by microiontophoretically injecting horseradish peroxidase into restricted areas of the facial nucleus. Projections were identified from thenucleus nervi hypoglossi, nucleus praepositus hypoglossi, nucleus raphe pallidus, nucleus intercalatus, medial nucleus of the solitary tract, dorsal motor nucleus of the vagus, neurons of genu of the facial nerve, ipsilateral red nucleus, and reticular formation of the midbrain to the facial nucleus. Projections from a number of other brain structures to the facial nucleus also received confirmation. A topographic map was drawn up, showing how brainstem and spinal cord afferents are distributed in the facial nucleus.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 18, No. 1, pp. 35–45, January–February, 1986.     

Neuronal mechanisms of interaction between the red nucleus and other brain stem structures

Axon collaterals of rubrospinal neurons running to many brain stem structures were identified in acute experiments on cats by a technique of intracellular recording of antidromic action potentials in conjunction with collision testing. A systemic principle of organization of rubrospinal influences and also a tendency toward synchronous arrival of rubrospinal impulses at various brain stem centers were demonstrated. Most of these centers are relay nuclei, sending direct afferent projections to regions of the cerebellum which, in turn, control activity of the red nucleus. Besides such a loop, effecting dynamic cerebellar control over motor function, transmission of somatosensory information from nuclei of the dorsal columns of the spinal cord directly to the red nucleus was demonstrated. Special features of mono- and polysynaptic EPSPs evoked by stimulation of nuclei of the dorsal columns indicate that such PSPs arise in different regions of the soma-dendritic membrane of red nucleus neurons. The mechanisms of integration of descending motor volleys by the red nucleus are discussed.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 16, No. 5, pp. 665–678, September–October, 1984.     

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.     

Electrophysiological features of facial motoneurons in cats

Antidromic activation of facial motoneurons in cats during stimulation of different branches of the facial nerve was studied by intracellular recording. Time and amplitude characteristics of individual components of the antidromic action potentials were analyzed and fast and slow after-potentials distinguished. Correlation was found between the duration of the descending phase of the SD spike, duration of its after-hyperpolarization, and the spike conduction time along the axon. Data were obtained to show absence of a recurrent collateral pathway in motoneurons of the facial nucleus. The functional significance of the after-potentials is discussed.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 10, No. 3, pp. 261–270, May–June, 1978.     

Spatial organization of inhibitory control of activity of vestibulospinal Deiters' neurons by Purkinje cells in the anterior lobe of the cerebellum

The topographical distribution of vestibulospinal neurons in Deiters' nucleus was investigated by a microelectrode method. By contrast with observations made in morphological experiments, the localization of antidromically identified vestibulocervical (C-neurons) and vestibulolumbar (L-neurons) cells was found not to be limited to the ventral middle and rostral third of the nucleus (the forelimb region) and caudodorsal part of the nucleus (hind limb region), but to include the whole of the ventral and dorsal half of the nucleus, respectively. The zones of localization of these two groups of neurons are not confined to a single layer: C-neurons are found in the dorsal half of the nucleus and L-neurons in its ventrocaudal part also. Analysis of the distribution of monosynaptic IPSPs arising in response to activation of Purkinje cells in the vestibulospinal neurons showed that C-neurons are controlled chiefly from the forelimb zone of the cerebellar cortex whereas L-neurons are controlled equally by inhibitory influences from the forelimb and hind limb zones of the anterior lobe of the cerebellar cortex.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 11, No. 1, pp. 54–64, January–February, 1979.     

Electrophysiological study of locus ceruleus projections to central cerebellar nuclei

Evoked response (field potentials) were recorded in all cerebellar nuclei when stimulating the locus ceruleus (LC). Response occurring in the dentate and fastigial nuclei were of considerably greater amplitude and were repeated at a higher rate than in the interstitial nucleus. Blockade of beta-adrenoreceptors led to clear-cut depression of response in the dentate and fastigial nuclei and increased response in the interstitial nucleus. Neuronal response to LC stimulation in the nuclei mainly took the form of inhibition of spontaneous discharges. A less pronounced response was observed in the interstitial nucleus. The findings obtained would indicate the presence of noradrenergic afferents reaching the cerebellar nuclei, where they are unevenly distributed.Kh. Anovyan Pedagogical Institute, Armenia SSR, Erevan. L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 1, pp. 39–44, January–February, 1989.     

Afferent connections of the dorsal magnocellularis area of the cat red nucleus

Location within the brain of retrogradely labeled neurons putting out projections from the dorsal magnocellularis area of the red nucleus was investigated by means of microiontophoretic injection of horseradish peroxidase into the dorsal magnocellularis area of the cat red nucleus. Projections were found from a number of hypothalamic nuclei, the centrum medianum, parafascicular and subthalamic nuclei, zone incerta, Forel's field, nucleus medialis habenulae, pontine and bulbar reticular formation, and the following midbrain structures: the central gray matter, superior colliculus, Cajal's interstitial nucleus, reticular formation, and the contralateral red nucleus. Projections were also identified proceeding from more caudally located structures: the cerebellar fastigial nucleus, facial nucleus, medial vestibular and dorsal lateral vestibular nuclei, and ventral horns of the spinal cord cervical segments. Connections between the substantia nigra and the red nucleus were clarified. Projections to the red nucleus from the cerebral cortex, interstitial and dentate (lateral) cerebellar nuclei, the nucleus gracilis and cuneate nucleus were found, confirming data presented in the literature. Bilateral trajectories of retrogradely labeled fiber systems are described.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 19, No. 6, pp. 810–816, November–December, 1987.     

Neuronal analysis of projections from trigeminal nucleus caudalis to the facial nucleus in cats

Properties of neurons of the trigeminal nucleus caudalis, with projections into the facial nucleus, were investigated in cats by a microelectrode technique. These neurons were found to be located mainly in the ventral parts of the trigeminal nucleus caudalis and in the adjacent lateral reticular formation. Monosynaptic and polysynaptic activation of efferent neurons of the trigeminal nucleus caudalis was found in response to pyramidal impulsation. Repeated discharges were recorded in the test neurons in response to stimulation of their axons, to direct stimulation of the trigeminal nucleus caudalis, and also to stimulation of the pyramidal tract and facial nerve. The synaptic mechanisms of regulation of motoneuron activity in the facial nerve nucleus are discussed.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 13, No. 3, pp. 264–269, May–June, 1981.     

Sources of thalamo-cortical afferents of the forelimb representation area in the first somatosensory zone of the cat cerebral cortex

Retrogradely labeled thalamic neurons—the sources of afferents in the focus of peak activity induced by radial nerve stimulation—were investigated in adult cats by means of microiontophoretic horseradish peroxidase injection into the first somatosensory zone of the cerebral cortex. Labeled cells were found mainly in the ventroposterolateral and a smaller proportion in the posteroventral medial thalamic nuclei. Labeled neurons were distributed in groups differing in their morphological parameters within these nuclei.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 20, No. 2, pp. 154–160, March–April, 1988.     

Study of pathways transmitting sympathetic-activating influences from hypothalamus to spinal cord

The properties of hypothalamic pathways activating sympathetic preganglionic neurons in the lateral horns of the spinal cord were studied in cats. This activation was shown to take place through reticulospinal sympathetic-activating neurons in the medulla. The possible zone of location of hypothalamic sympathetic-activating output neurons was shown by the scanning stimulation method to be in the posterolateral hypothalamus. Reticulospinal sympathetic-activating neurons in the medulla are probably excited monosynaptically by hypothalamo-sympathetic activating fibers projected on them.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 14, No. 3, pp. 307–314, May–June, 1982.     

Effect of local depression of inhibition on electrical activity of the spinal cord

The dorsal cord, dorsal root, and focal potentials in response to peripheral nerve stimulation were investigated in rats with local depression of inhibition in the left or right half of the lumbar segments produced by the action of tetanus toxin. The investigation was carried out at the stage of poisoning when excitation of the neuron population with disturbed inhibition caused generalized excitation of spinal and bulbar motoneurons. Experiments on spinal animals showed that if a cutaneous nerve is stimulated on the side affected by the toxin these responses have a greater amplitude and a much longer duration than those evoked by stimulation of the opposite nerve or responses in healthy rats. The maximal increase in amplitude and duration of the negative component of the focal potential corresponding to the time of the increased P wave of the dorsal cord potential was found in the ventral quadrant on the side affected by the toxin. Besides evoked focal potentials, spontaneous rhythmic negative waves also were recorded in this area. The mechanisms of spread of seizure activity from the focus of depressed inhibition are discussed and the structures generating spreading seizure activity are identified.     

Comparative study of sympathetic and parasympathetic firing in automatic nerves produced by stimulating different structures of the cat hypothalamus

It was discovered by making simultaneous recordings of evoked hypothalamic-parasympathetic and hypothalamic-sympathetic firing that sympathetic discharges in the splanchnic nerve and parasympathetic discharges in the pelvic nerve with minimum latency and lowest threshold level could be obtained by stimulating the posterolateral hypothalamus. It was also found that the focus of maximum neuronal activity produced by stimulating afferent visceral nerve fibers as well as the highest concentration of evoked efferent response in sympathetic and parasympathetic nerves were located in the same hypothalamic area. A working hypothesis was put forward that convergent polysensory hypothalamic neurons also act as divergent polyeffector constituents of the integrative system of the hypothalamovisceral reflex arc.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 19, No. 4, pp. 482–491, July–August, 1987.     

Synaptic processes produced in cat rubrospinal neurons by stimulating the cerebellar nucleus interprositus

The activity produced in red nucleus rubrospinal neurons by stimulating the cerebellar nucleus interpositus was investigated in cats anesthetized with nembutal. Analysis of field potentials together with summated and single EPSP following paired and frequency stimulation of this structure revealed facilitation at cerebello-rubral synapses. It was found that this facilitation was not mediated by changes in presynaptic volleys. It is suggested that modification of the effectiveness of transmission is determined by characteristic features of the operation of cerebellar synapses on red nucleus neurons.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 19, No. 5, pp. 630–636, September–October, 1987.     

Synaptic processes in facial motoneurons evoked by stimulation of the caudal trigeminal nucleus

Field potentials and postsynaptic potentials of facial motoneurons evoked by stimulation of the caudal trigeminal nucleus were investigated in acute experiments on cats by extra- and intra-cellular recording. Pre- and postsynaptic components of field potentials were found. Four types of motoneuron response were distinguished: EPSP with generation of single action potentials; a gradual shift of depolarization inducing grouped action potentials; a rhythmic discharge of action potentials arising at a low level of depolarization; and EPSPs or EPSP-IPSP sequences. The monosynaptic and (chiefly) polysynaptic nature of these responses was demonstrated. The possible mechanism of afferent control over facial motoneurons are discussed.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 12, No. 3, pp. 272–282, May–June, 1980.     

Effects of vasopressin and oxytocin on evoked dorsal horn cell activity in an isolated segment of spinal cord

During experiments on an isolated segment of the spinal cord of 2- to 3-week-old rats, a study was made of the effects of vasopressin and oxytocin on the activity of dorsal horn cells produced by stimulating the afferent root. Both field and action potentials were recorded in single cells. It was established that vasopressin and oxytocin produced reversible inhibition of the postsynaptic component of field potentials. The amplitude of potentials was reduced by 33–39% by vasopressin and by 12–34% using oxytocin. The effect of the test substances depended on the concentration used and the duration of their action on the brain. Both vasopressin and oxytocin reversibly depressed discharges of single dorsal horn cells evoked by stimulating the dorsal root. These two neuropeptides prolonged latency, and reduced the number of evoked potentials or completely suppressed response. A facilitatory effect was recorded in a small number of cells. We deduced from our findings that their hypothalamospinal neurohormonal system inhibits transmission of afferent impulses at the level of interneurons of the dorsal horn.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 17, No. 5, pp. 634–640, September–October, 1985.     

Synaptic mechanisms of the action of subcortical formations on motoneurons in cat facial nerve

Characteristics of the synaptic processes produced by stimulating the head of the caudate nucleus, theglocus pallidus, and the central amygaloid nucleus were investigated in motoneurons of the facial nerve during acute experiments on cats using intracellular recording techniques. It was found that stimulating the first two of these structures causes polysynaptic activation, while both mono- and polysynaptic excitation of facial nerve motoneurons are produced by stimulation of the central amygdaloid nucleus.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 17, No. 6, pp. 800–809, November–December, 1985.     

N-methyl-D-aspartate effect on spontaneous activity of 16–20-day-old chick embryo spinal cord

The effects of N-methyl-D-aspartate (NMDA) and the NMDA receptor antagonist, 2-amino-5-phosphonovaleric acid (2-APV), on spontaneous activity of dorsal and ventral roots (DR and VR, respectively) generated by isolated spinal cord from 16–20-day-old chick embryo were studied. This activity was synchronous oscillations of electrotonic potentials in DR and VR. There was no impulse activity in the VR. When NMDA was applied at 2–25 µM, the amplitudes of the oscillations increased, the impulse activities in VR and DR developed, and the tonic component of electrotonic potentials appeared. At 20 µM, 2-APV decreased both, the spontaneous and NMDA induced activity. After sectioning of the spinal cord, the neuronal network of the isolated dorsal arm conserved the capacity to generate spontaneous activity in the DR which increased after NMDA application. There was no rhythm in the ventral part of the spinal cord. The localization of the NMDA-sensitive neuronal network, generator of the rhythmic (motor) activity, in the spinal cord is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 2, pp. 205–213, March–April, 1991.     

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.     

Evoked activity of spinal neurons in the early period after sciatic nerve division

The character of dorsal horn motoneurons and interneurons evoked by stimulation of the dorsal root, and activity of Renshaw cells in response to stimulation of the ventral root were studied in albino rats in the lower lumbar segments of the spinal cord 5 days after sciatic nerve division. A significant increase in the mean amplitude of excitatory postsynaptic potentials of motoneurons was observed on the side of division of the nerve. No significant change in membrane potential and in the threshold of appearance of the action potential of these motoneurons took place. The mean number of action potentials and the duration of discharge of the Renshaw cells and dorsal horn interneurons likewise were not significantly changed.Dnepropetrovsk Medical Institute, Ukrainian Ministry of Health. Translated from Neirofiziologiya, Vol. 24, No. 3, pp. 306–314, May–June, 1992.     

Glial origin of the slow negative potential of the direct cortical response: Microelectrode study and mathematical analysis

The slow negative potential of the direct cortical response is similar in its shape, time course, and relationship to repetitive stimulation to depolarization of cortical glial cells but differs from the IPSP of cortical neurons. According to the results of digital spectral (frequency) analysis, the basis of the slow negative potential is the glial component formed by summation of components which coincide with glial depolarization processes with an accuracy determined by a constant factor. The much smaller component (as regards relative contribution) is the indirect result of the development of an IPSP in the neurons.I. S. Beritashvili Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 14, No. 1, pp. 76–84, January–February, 1982.