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.     

Synaptic potentials of motoneurons of the masseter muscle

Postsynaptic potentials of 93 motoneurons of the masseter muscle evoked by stimulation of different branches of the trigeminal nerve were studied. Stimulation of the most excitable afferent fibers of the motor nerve of the masseter muscle evoked monosynaptic EPSPs with a latent period of 1.2–2.0 msec, changing into action potentials when the strength of stimulation was increased. A further increase in the strength of stimulation produced an antidromic action potential in the motoneurons with a latent period of 0.9 msec. In some motoneurons polysynaptic EPSPs and action potentials developed following stimulation of the motor nerve to the masseter muscle. The ascending phase of synaptic and antidromic action potentials was subdivided into IS and SD components, while the descending phase ended with definite depolarization and hyperpolarization after-potentials. Stimulation of cutaneous branches of the trigeminal nerve, and also of the motor nerve of the antagonist muscle (digastric) evoked IPSPs with a latent period of 2.7–3.5 msec in motoneurons of the masseter muscle. These results indicate the existence of functional connections between motoneurons of the masseter muscle and its proprioceptive afferent fibers, and also with proprioceptive afferent fibers of the antagonist muscle and cutaneous afferent fibers.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 1, No. 3, pp. 262–268, November–December, 1969.     

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 stimulating the superior colliculus on motoneurons of the neck muscle in the cat

Postsynaptic potentials produced by stimulating three sites of the midbrain superior colliculus were examined in motoneurons innervating the sternocleidomastoid, the trapezius, and the platysma cervical muscles in anesthetized cats. Stimulating the ipsilateral colliculus produced EPSP in the motoneurons as well as action potentials with a latency of 1.5–3.5 msec, averaging 2.6 ± 0.1 msec. Stimulation of the contralateral colliculus evoked EPSP with a latency of 1.5–3.2 msec and averaging 2.1 ± 0.1 msec together with IPSP with latency ranging from 2.6 to 5.0 msec. It is postulated that these postsynaptic responses are both monosynpatic and bisynaptic in nature. This type of synaptic action is assumed to be one of the mechanisms responsible for coordinated head movements produced by tectofugal impulses.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 2, pp. 197–202, March–April, 1986.     

Membrane electrical properties of motoneurons innervating the masseter muscles in rats

Membrane potentials and action potentials evoked by antidromic and direct stimulation were investigated in motoneurons of the trigeminal nucleus in rats innervating the masseter muscle. This motor nucleus was shown to contain cell populations with high and low membrane potentials. The responses of cells of the first group had shorter latent periods of their antidromic action potentials, a longer spike duration, and a lower amplitude and shorter duration of after-hyperpolarization than responses of cells of the second group, and the input resistance of their membrane also is lower. The bimodal character of distribution of electrophysiological parameters of motoneurons in the trigeminal nucleus indicates that "fast" and "slow" fibers of the masseter muscles may be innervated by different types of nerve cells.N. A. Semashko Moscow Medical Stomatological Institute. Translated from Neirofiziologiya, Vol. 13, No. 3, pp. 270–274, May–June, 1981.     

Synaptic effects of contralateral somatic afferents on spinal motoneurons

Electrical activity of flexor and extensor alpha-motoneurons of the lumbar segments of cat's spinal cord as recorded intracellularly during electric stimulation of afferents of the contralateral posterior limb. Contralateral postsynaptic potentials (PSP) were shown to be evoked by activation of cutaneous and high-threshold muscle afferents. The high-threshold afferents of various muscle nerves participate to varying degrees in the generation of contralateral PSP. Contralateral inhibitory postsynaptic potentials (IPSP) were recorded in both flexor and extensor motoneurons along with contralateral excitatory postsynaptic potentials (EPSP). There are no fundamental differences in their distribution between flexor and extensor neurons. Inhibitory influences as a rule are predominant in both during the first 20 msec, and EPSP are predominant in the interval between 20 and 100 msec. The balance of excitatory and inhibitory pathway activity was found to be not as stable as that of the homolateral pathways.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 3, No. 4, pp. 418–425, July–August, 1971.     

Synaptic mechanisms of central control of motoneuronal activity in the facial nerve nucleus

The responses of motoneurons of the facial nerve nucleus (FNN), evoked by stimulations of the oculomotor nerve nucleus, Edinger-Westphal's nucleus,substantia nigra, and entopeduncular nucleus, were studied in acute experiments on anesthetized and immobilized cats. The FNN motoneurons were identified by their antidromic activation after stimulation of various branches of the facial nerve. Stimulation of the oculomotor nerve nucleus, Edinger-Westphal's nucleus, and ipsi- or contralateral parts of thesubstantia nigra evoked mono- and polysynaptic EPSP in the FNN motoneurons, while stimulation of the entopeduncular nucleus elicited only polysynaptic EPSP. The influences from the above structures were shown to converge on the same FNN motoneurons. The findings are discussed considering morphological peculiarities of the afferent inputs to the FNN.Neirofiziologiya/Neurophysiology, Vol. 27, No. 2, pp. 116–125, March–April, 1995.     

Monosynaptic excitation of motoneurons of the accessory nerve nucleus by reticulofugal impulses

Acute experiments on cats anesthetized with chloralose and pentobarbital showed that excitation of fast-conducting (130 m/sec) reticulospinal fibers, arising during stimulation of the ipsilateral medullary reticular gigantocellular nucleus evoked monosynaptic EPSPs in motoneurons of the accessory nerve nucleus. The EPSPs had latent periods of between 0.6 and 1.0 msec (mean 0.7 msec), they reached their maximal amplitude (4.0 mV) after 2.0–2.5 msec, and lasted about 10 msec. The EPSPs underwent only weak potentiation through the different types of stimulation of the gigantocellular nucleus and were not transformed into action potentials.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 1, pp. 62–66, January–February, 1980.     

Rubrofugal activation of motoneurons of the cat accessory nucleus

Postsynaptic potentials evoked in accessory nerve motoneurons by stimulation of the ipsilateral and contralateral red nuclei were investigated in acute experiments on cats anesthetized with chloralose and pentobarbital. Polysynaptic EPSPs with latent periods of 5.2 to 16 (mean 9.1 ± 0.7) msec and from 5.5 to 18 (mean 10.3 ± 0.9) msec, respectively, appeared in motoneurons of the accessory nerve in response to stimulation of the contralateral and ipsilateral red nuclei. A minimum of two or three stimuli was necessary to produce EPSPs in these motoneurons. In response to single stimulation of the contralateral and ipsilateral red nuclei EPSPs appeared in four motoneurons of the trapezius muscle with latent periods of 2.5 to 5.0 and 3.0 to 5.2 msec, respectively. An increase in the number of stimuli led to action potential generation by motoneurons. The functional role of such activation is discussed.A. A. Bogomolets Institue of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 14, No. 5, pp. 532–536, September–October, 1982.     

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.     

Corticofugal postsynaptic influences on red nucleus neurons

The responses of red nucleus neurons to stimulation of the sensorimotor cortex was studied on nembutal-anesthetized cats. Most of the rubrospinal neurons were identified according to their antidromic activation. Stimulation of the sensorimotor cortex was shown to evoke in the red nucleus neurons monosynaptic excitatory potentials with a latency of 1.85 msec, polysynaptic excitatory potentials (EPSP), and inhibitory postsynaptic potentials (IPSP) with a latency of 9–24 msec. The EPSP often produced spikes. The probability of generation of spreading excitation is greater with motor cortex stimulation. The monosynaptic EPSP are assumed to arise under the influence of the impulses arriving over the corticorubral neurons as a result of excitation of axodendritic synapses. The radial type of branching of red nucleus neurons facilitates the transition from electrotonically spreading local depolarization to an action potential triggered by the initial axonal segment. Polysynaptic EPSP and IPSP seem to be a result of activation of fast pyramidal neurons whose axon collaterals are connected via interneurons with the soma of the red nucleus neurons.L. A. Orbeli Institute of Physiology of the Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 3, No. 1, pp. 43–51, January–February, 1971.     

Role of different types of fibers of the infraorbital nerve in synaptic activation of masseter and digastric motoneurons

Postsynaptic potentials of motoneurons of the masseter and digastric muscles evoked by stimulation of the infraorbital nerve with a strength of between 1 and 10 thresholds were investigated in cats anesthetized with a mixture of chloralose and pentobarbital. Depending on their ability to be activated by low-threshold afferents of this nerve, motoneurons of the masseter were divided into two groups. Stimuli with a strength of 1.2–2.5 times above threshold for the most excitable fibers of the infraorbital nerve evoked short-latency EPSPs in the motoneurons of the first group; a further increase in stimulus strength (3–9 thresholds) led to the appearance of IPSPs with latent periods of 2.8–3.5 msec. Motoneurons of the second group responded to stimulation of the infraorbital nerve with a strength of 3–9 thresholds by IPSPs whose latent periods varied from 6 to 8 msec. Stimuli below 3 thresholds in strength evoked no responses in these motoneurons. Stimulation of the infraorbital nerve with pulses of between 1 and 2 thresholds in strength evoked EPSPs in digastric motoneurons, but an increase in the strength of stimulation led to action potential generation. The presence of many excitatory and inhibitory inputs formed by afferent fibers of different types evidently provides a basis for functional diversity of jaw-opening and jaw-closing reflexes.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 6, pp. 596–603, November–December, 1980.     

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.     

Postsynaptic potentials of motoneurons evoked by rubrofugal impulsation in the hypoglossal nucleus of the cat

The effect of stimulation of the ipsilateral and contralateral red nuclei on motoneurons of the hypoglossal nucleus was studied in cats anesthetized with chloralose and pentobarbital. In 35 (69%) of the 51 motoneurons tested, PSPs were generated in response to stimulation of the red nuclei by series of 3 to 5 stimuli of threshold strength and with a frequency of 500–600/sec. Of this number, 33 motoneurons responded to stimulation by EPSPs, whose latent periods varied from 3.5 to 14.0 msec (mean value for the ipsilateral red nucleus 5.7±0.75, for the contralateral nucleus 6.8±0.8 msec), whereas two motoneurons responded (after 6.2 msec) by IPSPs. Of the 35 motoneurons responding to stimulation of the red nuclei, stimulation of the lingual nerve evoked EPSPs in 31 and IPSPs in 4 (two of them were inhibited by rubrofugal impulses). IPSPs were generated as a result of stimulation of the lingual nerve in 16 motoneurons which did not respond to rubrofugal impulses.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 1, pp. 62–66, January–February, 1978.     

Monosynaptic excitory postsynaptic potentials in thoracic motoneurons under reticulospinal influences

We studied synaptic processes in motoneurons of thoracic segments (T_IX-T_XI) evoked by stimulation of the medial area of the giant-cell reticular nucleus in decerebrated cats. Monosynaptic EPSP were recorded in the majority of investigated motoneurons upon activation of the most rapidly conducting reticulospinal fibers. In some cells, such monosynaptic EPSP were accompanied by late EPSP or IPSP. Amplitude of monosynaptic EPSP attained 5 mV, but this value usually was insufficient for development of an action potential. Upon summation of single monosynaptic EPSP, the membrane potential reached the critical level and an action potential arose in the motoneuron. The efficiency of summary processes evoked by stimulation of the reticular formation exceeded the intensity of synaptic processes that arise in thoracic motoneurons on stimulating the nucleus of Deiters. Functional characteristics of reticular and vestibular monosynaptic EPSP are discussed in the work.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 1, No. 3, pp. 243–252, November–December, 1969.     

Action potentials of masseter motoneurons evoked by stimulation of low-threshold infraorbital nerve afferents in cats

In cats anesthetized with chloralose and pentobarbital stimulation of the infraorbital nerve by a volley of 3 or 4 stimuli 1.2 times stronger than the threshold for excitation of A-fibers caused the generation of action potentials in motoneurons of the masseter muscle if the frequency of stimuli in the volley exceeded 300/sec. Paired stimuli with a strength of 2.0 thresholds, and with an interval of 1.3–4.0 msec between stimuli, led to generation of an action potential by the motoneurons. If the interval exceeded 4 msec stimulation with a strength of 1.2–2.0 thresholds caused biphasic facilitation of the second EPSP with a facilitation factor of between 0.2 and 1.0. The small number of stimuli, combined with their high frequency in the volley, required for action potential generation by masseter motoneurons suggests that they are due to activation of A-fibers of the infraorbital nerve connected with fast-adapted receptors of the vibrissae.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 4 pp. 385–389, July–August, 1978.     

Rubrospinal synaptic influences on the lumbar motoneurons of the rat

Intracellular recording was employed in experiments on rats with the nervous system intact and after acute pyramidotomy to study the postsynaptic effects produced in the lumbar motoneurons on stimulation of the nucleus ruber. Stimulation of this nucleus with single stimuli and with a short series of stimuli caused excitatory and inhibitory postsynaptic potentials (EPSP and IPSP) to develop in the motoneurons. Most of the EPSP recorded were disynaptic, but response development involved a monosynaptic segmental delay in five of the 124 cells that exhibited EPSP. A capacity for high-frequency potentiation was a characteristic feature of the disynaptic excitatory and inhibitory effects. Transmembrane polarization of the motoneurons had a marked influence on the amplitude of the disynaptic EPSP and IPSP. The properties of the disynaptic rubrospinal influences were similar to those described for the cat.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 3, No. 3, pp. 266–273, May–June, 1971.     

EPSPs of masseter motoneurons evoked by stimulation of low-threshold infraorbital nerve afferents in cat

Stimulation of the infraorbital nerve at strengths 1.4–2.5 times higer than the threshold of excitation of A fibers in cats anesthetized with chloralose and pentobarbital evoked EPSPs with an amplitude up to 3.0 mV and a duration of 9–15 msec in 69% of masseter motoneurons after 1.5–3.0 msec. These EPSPs were complex and formed by summation of simpler short-latency and long-latency EPSPs. The short-latency EPSPs appeared in response to infraorbital nerve stimulation at 1.1–1.5 thresholds and had a slow rate of rise (2.5–4.5 msec, mean 3.7±0.4 msec), low amplitude (under 2.0 mV), and short duration (5–6 msec). Their latent period varied from 1.5 to 3.0 msec (mean 2.1±0.2 msec). The shortness of the latent period and its constancy during stimulation of the nerve at increasing strength, and also the character of development of facilitation and inhibition of the EPSP during high-frequency stimulation suggests that these EPSPs are monosynaptic. The slow rate of rise suggested that these EPSPs arise on distal dendrites of the motoneurons. Long-latency EPSPs appeared 7–9 msec after stimulation of the infraorbital nerve at 1.1–1.5 thresholds. Their amplitude reached 1.5–2.0 mV and their duration 7–9 msec. The long duration of the latent period combined with low ability to reproduce high-frequency stimulation (up to 30/sec) points to the polysynaptic origin of these EPSPs.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 9, No. 6, pp. 583–591, November–December, 1977.     

Postsynaptic potentials of facial motoneurons evoked by afferent and corticofugal impulses

Postsynaptic potentials of motoneurons in the facial nerve nucleus, evoked by stimulation of the cranial nerves (trigeminal, hypoglossal, facial) and of the sensomotor cortex were investigated in cats anesthetized with chloralose and pentobarbital. Two functionally opposite groups of motoneurons were found to exist in the facial nucleus. Stimulation of the afferent nerves and cortex evoked the appearance of EPSPs in the first of these groups and IPSPs in the second. The latency and duration of the PSPs indicate that afferent and corticofugal impulses reach the facial motoneurons along polysynaptic pathways. Interneurons on which wide convergence of influences travelling along afferent fibers and of the cortex, were found in the region of the facial nucleus. The possible neuronal pathways concerned with the transmission of afferent and corticofugal impulses to the facial motoneurons are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol.4, No.4, pp. 391–400, July–August, 1972.     

Monosynaptic excitation of facial motoneurons during electrical stimulation of the red nucleus

Synaptic effects of the red nucleus on motoneurons of the facial nucleus were studied in cats. Impulses from the red nucleus activate motoneurons innervating the auricular, buccal, and orbicularis oculi muscles. Monosynaptic EPSPs appeared in all motoneurons which responded to stimulation. Their mean latent period was 1.5±0.04 msec, duration 12.3 ± 0.34 msec, and rise time between 1.5 and 3.2 msec. Repetitive stimulation of the red nucleus led to marked facilitation of the testing EPSP. Facilitation was maximal when the interval between stimuli was 3.5 msec; it was reduced by either a decrease or an increase in the interval. The functional role of the monosynaptic connections of neurons of the red nucleus and of the facial motoneurons is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 3, pp. 272–279, May–June, 1972.