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.     

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.     

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 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.     

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.     

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.     

Properties of action potentials in Drosera tentacles

Summary Action potentials of Drosera tentacles resemble those of vertebrate peripheral nerves in that they appear to be comprised of relatively uniform spikes, variable shoulders or negative after-potentials, and variable positive after-potentials. The peaking of the spike corresponds to a period of great refractoriness, while action potentials of low amplitude may be fired readily during the negative after-potential. The action potentials fired during the negative after-potential appear to be unlike those of peripheral nerves in that they are of abnormally brief duration. Also apparently different from the case in peripheral nerves is the dependence of the duration of an action potential on the interval separating it from the preceding action potential.Action potentials propagate from the neck of the stalk to its base at about 5 mm s^-1 at room temperature. Propagation may be reversed artificially, consistent with the possibility that the neuroid cells are electrically coupled.     

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.     

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.     

Inhibition in the fish olfactory bulb

Inhibition in the olfactory bulb of the carp was studied by recording potentials from secondary neurons intracellularly. Three types of inhibition — trace, early, and late — can arise in neurons of the olfactory bulb. Trace inhibition corresponds to hyperpolarization about 20 msec in duration, which is closely connected with the spike, but it is not after-hyperpolarization but an IPSP. Early and late inhibition correspond to IPSPs of different parameters. The first has a latency of 0–50 msec (relative to the spike) and a duration of 60–400 msec; the corresponding values for the second are 100–400 msec and 0.5–3 sec. The possible mechanisms of these types of inhibition are discussed.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 3, No. 6, pp. 650–656, November–December, 1971.     

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.     

Influence of forelimb afferents on the activity of lumbar spinal-cord motoneurons

Experiments were conducted on anesthetized cats with microelectrode recording to study the synaptic responses that develop in the lumbar motoneurons on stimulation of the afferent fibers of groups II and III in the nerves of the ipsilateral and contralateral forelegs. Stimulation of these afferents evoked predominantly inhibitory postsynaptic potentials (IPSP) in the extensor motoneurons and excitatory postsynaptic potentials (EPSP) in the flexor motoneurons. A basically inhibitory change in the rhythmic background activity developed under the influence of descending impulsation. The duration of the total inhibition of "spontaneous" motoneuron activity corresponded to the duration of the inhibitory influences exerted by the forelimb flexor-reflex afferents (FRA) on the interneurons. The interaction of the descending and segmental PSP resulted in inhibition and facilitation of the segmental responses in the motoneurons. The ultimate result of this interaction was determined by the shifts in the membrane potential of the motoneuron and by the effects created in the interneurons.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 3, No. 1, pp. 58–67, January–February, 1971.     

Participation of midbrain periaqueductal gray matter in defense conditioning in rats

Responses of neurons of the periaqueductal gray matter (PAG) were studied in chronic experiments on cats during formation and extinction of a defensive conditioned reflex to sound and its differential inhibition. In response to conditioned stimulation these neurons developed phasic-tonic spike responses up to 3 sec in duration. During combination of stimuli these responses were formed long before the conditioned reflex and disappeared long after the latter was extinguished. In the case of an established conditioned reflex, the onset of spike responses occurred 100–200 msec before the appearance of motor responses. An increase in spike activity of tonic character in neurons of PAG preceded voluntary movements by 100–500 msec. The responses of these neurons to presentation of a differential stimulus consisted of groups of spikes 150–200 msec in duration. They were formed with difficulty, and their manifestation was made even more difficult by an interruption during the experiment and by preceding positive stimuli. On the basis of the results a conditioned reflex can be regarded as the result of a multilevel hierarchic process of readjustment of unit activity, which begins in the nonspecific structures of the midbrain.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 15, No. 3, pp. 278–287, May–June, 1983.     

Effect of pH changes on after potentials of single frog Ranvier nodes

In experiments on single nodes of Ranvier of isolated frog nerve fibers a decrease in pH of the medium to 5 caused a small increase in after-depolarization but an increase in pH to 9 caused virtually no change in it. The after-hyperpolarization arising in potassium-free Ringer's solution was abolished by a decrease in pH but remained substantially unchanged as a result of an increase in pH; posttetanic hyperpolarization was reduced in amplitude and slightly increased in duration by a decrease in pH, but not appreciably changed by an increase in pH. It is concluded that the character of changes in after-potentials of single nodes of Ranvier of isolated nerve fibers in medium of different pH is entirely determined by the influence of this factor on the kinetics of the potassium permeability of the excitable membrane.I. N. Ul'yanov Pedagogic Institute, Ul'yanovsk. Translated from Neirofiziologiya, Vol. 8, No. 1, pp. 62–66, January–February, 1976.     

Spike generation by spinal neurons evoked by sinusoidal depolarization in cats

Dynamic characteristics of transformation of cell membrane depolarization by spinal neurons into spike discharge frequency were investigated in anesthetized cats. Neurons were activated by sinusoidally modulated currents passed through an intracellular microelectrode. Frequency analysis of this transformation for motoneurons was carried out within a modulation frequency range of 0.2–10 Hz. Frequency characteristics were determined with respect to parameters of the first harmonic of the evoked firing rate; the region of values of current fluctuations was chosen on the linear part of the current intensity versus firing rate characteristic curve. Changes in amplitude characteristics did not exceed 5 dB in absolute terms; at the same time the phase lead of the output signal increased with a rise of frequency. At a frequency of 0.2 Hz phase shifts were virtually absent, but at frequencies of 1, 5, and 10 Hz they amounted to 32, 50, and 83° on average respectively. Transformation of membrane depolarization by neurons into spike discharge frequency is characterized by essentially nonlinear properties, due in particular to the absence of a dynamic component of the response to a negative rate of change of depolarizing current. The frequency characteristics of spike activity of neurons of the motor system are discussed from the standpoint of possible correction of dynamic properties of the whole system at the single unit level.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Dnepropetrovsk State University. Translated from Neirofiziologiya, Vol. 14, No. 1, pp. 35–42, January–February, 1982.     

On the role of the spinal afferent neuron as a generator of extracellular current

The prediction that a system of currents flows between the dorsal column and the dorsal root due to differences in their after-potentials was found to be consistent with the experimental findings. The form, magnitude, duration, and sign of the electrotonic component DRα fulfill the requirements of the postulated system. A contribution of tract after-potentials to the evoked potential of intramedullary structures is indicated. It is a conclusion of this and previous studies that profound changes occur in certain membrane properties of myelinated primary afferent axons as they penetrate the central nervous system. The working concept of abrupt intraaxonal junctional regions is therefore justifiable.     

Factors responsible for multiple discharge of motoneurons in the facial nucleus in cats

The multiple discharge evoked by stimulation of the caudal trigeminal nucleus in motoneurons of the cat facial nucleus was investigated by an intracellular recording method in acute experiments on cats. The multiple discharge was shown to arise on the basis of gradual depolarization of the motoneuron membranes produced as a result of effective summation of high-frequency excitatory influences arriving from the caudal trigeminal nucleus. Factors facilitating the development of this process are the dendritic localization of synaptic endings of projection neurons of the caudal trigeminal nucleus, the dendritic origin of delayed depolarization processes, and the high input resistance of the motoneuron membrane in the facial nerve nucleus.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 13, No. 5, pp. 520–530, September–October, 1981.     

Afterhyperpolarization–firing rate relation of turtle spinal neurons

This study addressed the afterhyperploarization–firing rate relationship of unanesthetized turtle spinal motoneurons and interneurons. The afterhyperploarization of their solitary action potential at rheobase was compared to that during the cells minimum and maximum firing rates. Like previous mammalian findings, afterhyperpolarization duration and area at rheobase were 32 and 19% less for high- versus low-threshold motoneurons. Contrariwise, maximum firing rate was two times less for the high-threshold group. Other new findings were that for high- versus low-threshold interneurons, afterhyperpolarization duration and area were 25 and 95% less, and maximum firing rate 21% higher for the high-threshold group. For combined motoneurons versus interneurons, there were no differences in afterhyperpolarization duration and area at rheobase, whereas maximum firing rate was 265% higher for the interneurons. For high-threshold motoneurons alone, there were significant associations between minimum firing rate and afterhyperpolarization duration and area measured at rheobase. In summary, this study showed that (1) the afterhyperploarization values of both turtle spinal motoneurons and interneurons at rheobase provided little indication of their corresponding values at the cells minimum and maximum firing states, and (2) the evolution of afterhyperploarization from rheobase to maximum firing state differed both qualitatively and quantitatively for motoneurons versus interneurons.     

After-Potentials and Large Depolarizations of Single Nodes of Ranvier Treated with Veratridine

Potential differences between normal nodes of Ranvier (single fiber from the sciatic nerve of the frog, air-gap method) and a node exposed to 1 to 2.5 x 10^-6 gm veratridine per ml were measured. Negative after-potentials occurred immediately after application of the alkaloid when spike configuration and resting potential were virtually unchanged. The after-potentials decreased in magnitude and their time constant increased as the resting membrane was depolarized either by outward currents or by a train of impulses. Increase of (Na)_o markedly increased the amplitude of the after-potential. After prolonged application of veratridine or with higher concentrations, a large slow depolarization (rate of potential change about 7 mv per second) could be triggered by a train of impulses or even a single spike. This depolarization could promptly be terminated by withdrawing Na. It is concluded that, once the nodal membrane has become permeable to Na (as during a spike), veratridine prevents the normal return of P_Na to its resting value.