Contribution of antidromic efferent-fiber excitation to mass spinal potentials in the cat

The contribution of antidromic excitation of motoneurons to cord dorsum potentials (CDP) was studied in the spinal cord of anesthetized cats. It was shown that stimulation of ventral roots (VR) or peripheral nerves following deafferentiation of a number of segments by crosscutting of dorsal roots on the dorsal surface evokes appreciable positive-negative CDP (VR-CDP). Under intact conditions, VR effects of antidromic stimulation of efferent fibers brings appreciable input to the initial "fast" CDP component (the "afferent" peak); input values for the main mixed nerves of the hindlimb are presented. After conditioning stimulation of a mixed nerve, VR-CDP undergo inhibition with two maximums, associated with blocking of the effects of antidromic excitation of efferents by orthodromic mono- and polysynaptic reflex discharges of motoneurons. The hypothesis that intactness of efferents in nerves under stimulation can be determined from an analysis of initial CDP components is stated.Scientific-Research Institute of Biology, Dnepropetrovsk State University, Dnepropetrovsk. Translated from Neirofiziologiya, Vol. 23, No. 6, pp. 655–661, November–December, 1991.     

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.     

Responses of motoneurons undergoing chromatolysis

The delayed and asynchronous firing of chromatolytic motoneurons in response to group I afferent volleys is shown to be evoked monosynaptically, there being an abnormally long and variable delay between onset of monosynaptic action and generation of impulse discharge. Intensity of monosynaptic excitatory action is reduced, and considerable variability in the form of successively evoked postsynaptic potentials is often observed. No evidence has been found for the development of excitatory group I polysynaptic pathways. Reduction in responsiveness of finer dendrites is indicated by the feeble "d" response evoked by an antidromic volley in a chromatolytic motor nucleus. Antidromic impulses appear to invade the cell bodies and coarse dendrites, but die out at points short of the normal extent of dendritic invasion. Vigorous firing of Renshaw cells can be elicited by antidromic volleys. Chromatolytic motoneurons appear to maintain reasonably normal resting membrane potentials, but are more susceptible to damage than are normal cells. Action potentials are large and usually overshoot the resting potential level. Post spike potentials are similar to those of normal cells except for a less prominent, or absent, early phase of depolarisation. In contrast with the reduced responsiveness of peripheral dendrites, there is a lowered threshold for antidromic and segmental reflex synaptic activation of the more central regions, probably the cell bodies and nearby coarse dendrites, of motoneurons undergoing chromatolysis.     

Synaptic effects evoked in motoneurons by stimulation of single propriospinal neurons

Experiments on cats with simultaneous extracellular recording, stimulation of single propriospinal neurons, and intracellular recording of unitary postsynaptic potentials from motoneurons, followed by computer averaging showed that direct stimulation of individual propriospinal cells receiving mono- and disynaptic influences from the medial reticular formation can evoke monosynaptic EPSPs and IPSPs in lower lumbar motoneurons. The amplitude of these EPSPs was 49.6±6.0 and of the IPSPs 28.9±2.9 µV and their synaptic delay was 0.34±0.05 msec. The same propriospinal neuron of the ventral horn of the upper lumbar segments may be connected with several motoneurons of the hind limb muscles.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 9, No. 3, pp. 300–306, May–June, 1977.     

Changes in postsynaptic responses in spinal motoneurons during repetitive stimulation of the locus coeruleus

Experiments on cats anesthetized with chloralose showed that repetitive stimulation of the locus coeruleus is accompanied by a decrease in IPSPs evoked by stimulation of flexor reflex afferents in extensor motoneurons. The effect appeared 600 msec after the beginning of stimulation and reached its maximum after 1500–2000 msec. Repetitive stimulation of the locus coeruleus did not change the membrane potential and did not affect EPSPs or IPSPs evoked by stimulation of low-threshold muscle afferents; EPSPs due to activation of high-threshold cutaneous and muscle afferents likewise remained unchanged. Repetitive stimulation of more central regions of the brain stem was accompanied not only by a decrease in IPSPs evoked by stimulation of flexor reflex afferents in extensor motoneurons, but also by a decrease in amplitude of EPSPs arising in response to stimulation of these same afferents in flexor motoneurons. These effects were not connected with activation of monoaminergic structures, for unlike effects arising during stimulation of the locus coeruleus, they were also found in previously reserpinized animals.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 14, No. 1, pp. 51–59, January–February, 1982.     

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.     

Pyramidal and extrapyramidal synaptic effects upon chronically deafferented motoneurons of the spinal cord of a cat

By means of intracellular recording technique, studies have been made of the electrical activity of -motoneurons of the seventh lumbar segment in cats with chronic rhizotomy of the dorsal root fibers (L₄-S₂). Postsynaptic potentials of the reticular formation of the midbrain, medulla, and ventral columns of the spinal cord were compared with the reactions recorded from nonoperated animals; these potentials were evoked by stimulation of the motor cortex, red nucleus, and Deuters' nuclei. Deafferentiation did not cause statistically reliable variations in the amplitude of the descending monosynaptic E PSPs. Extrapyramidal short-latent disynaptic E PSPs and IPSPs remained also practically unchanged, while the responses of deafferented motoneurons to cortico-spinal impulses were considerably facilitated; this effect was retained in pyramidal cats. Deafferentation was not accompanied by variations in the dependence of the discharge frequency on the depolarizing current strength or by the variation in the threshold and input resistance of the motoneuron membranes. This suggests that intensification of the pyramidal synaptic action upon deafferented motoneurons was caused by the variation on the intermediate neuronal level.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 1, No. 1, pp. 35–46, July–August, 1969.     

Analysis of long cortical evoked potentials

Evoked potentials arising in the motor cortex in response to its direct stimulation (dendritic and slow negative potentials), to stimulation of the ventrolateral (primary response) and intralaminar (nonspecific response) thalamic nuclei, and to stimulation of the pyramidal tracts (antidromic response), and also postsynaptic responses of neurons corresponding to them were studied in acute experiments on curarized cats. Evoked potentials arising in response to direct cortical stimulation and also to stimulation of the specific and nonspecific thalamic nuclei and pyramidal tracts were recorded from the same point of the motor cortex, and the corresponding intracellular responses were recorded from the same neuron. Slow negative potentials arising under these conditions of stimulation and the IPSPs corresponding to them were shown to have an identical time course. The results show that slow negative potentials are a reflection of hyperpolarization of pyramidal neurons. It is suggested that the individual components of responses evoked by direct stimulation of the cortex and thalamic nuclei have a common genesis.I. S. Beritashvili Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 14, No. 2, pp. 115–121, March–April, 1982.     

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.     

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.     

Convergence of corticospinal and rubrospinal influences on cervical motoneurons

Synaptic responses of 121 identified cervical motoneurons to stimulation of the pyramidal tract and red nucleus were investigated by intracellular recording in cats. Responses of EPSP or EPSP-IPSP type were predominant in motoneurons of distal groups of muscles and proximal flexors, while responses of IPSP type were predominant in motoneurons of the proximal extensors. The minimal effective number of stimuli for most motoneurons was 2 or 3. The mean latent period, counted from the first stimulus in the series, was 7.86 msec for EPSPs for stimulation of the pyramidal tract and 7.91 msec for stimulation of the red nucleus, while the corresponding periods for IPSPs were 8.68 and 8.75 msec. The segmental delay of 1.3–2 msec for EPSPs and IPSPs generated in certain motoneurons in response to stimulation of both structures indicates that the shortest pathway for transmission of activity from the fibers of these tracts to the motoneurons may be disynaptic. At the same time, the possible presence of an additional neuron for most inhibitory pathways cannot be ruled out. Analysis of the results also suggests the presence of a common interneuronal apparatus for both systems.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol.3, No.6, pp. 599–608, November–December, 1971.     

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.     

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.     

Responses of medial geniculate body neurons to auditory cortical stimulation

Extracellular and intracellular unit responses of thepars principalis of the medial geniculate body to stimulation of the first (AI), second (AII), and third (AIII) auditory cortical areas were studied in cats immobilized with D-tubocurarine. In response to auditory cortical stimulation both antidromic (45–50%) and orthodromic (50–55%) responses occurred in the geniculate neurons. The latent period of the antidromic responses was 0.3–2.5 msec and of the orthodromic 2.0–18.0 msec. Late responses had a latent period of 30–200 msec. Of all neurons responding antidromically to stimulation of AII, 63% responded antidromically to stimulation of AI also, confirming the hypothesis that many of the same neurons of the medial geniculate body have projections into both auditory areas. Orthodromic responses of geniculate neurons consisted either of 1 or 2 spikes or of volleys of 8–12 spikes with a frequency of 300–600/sec. It is suggested that the volleys of spikes were discharges of inhibitory neurons. Intracellular responses were recorded in the form of antidromic spikes, EPSPs, EPSP-spike, EPSP-spike-IPSP, EPSP-IPSP, and primary IPSP. Over 50% of primary IPSP had a latent period of 2.0–4.0 msec. It is suggested that they arose through the participation of inhibitory interneurons located in the medial geniculate body.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 8, No. 1, pp. 5–12, January–February, 1976.     

Unit responses of the first and second somatosensory areas to stimulation of the ventroposterior thalamic nucleus

Single unit responses of the first (SI) and second (SII) somatosensory areas to stimulation of the ventroposterior thalamic nucleus (VP) were investigated in cats immobilized with D-tubocurarine. In response to VP stimulation 12.0% of reacting SI neurons and 9.5% of SII neurons generated an antidromic spike. In most antidromic responses of both SI and SII neurons the latent period did not exceed 1.0 msec. The minimal latent period of spike potentials during orthodromic excitation was 1.5 msec in SI and 1.7 msec in SII. Neurons with an orthodromic spike latency of not more than 3.0 msec were more numerous in SI than those with a latency of 3.1–4.5 msec. The ratio between the numbers of neurons of these two groups in SII was the opposite. In SII there were many more neurons with a latency of 5.6–8.0 msec than in SI. EPSPs appeared after a latent period of 1.1–9.0 msec in SI and of 1.4–6.6 msec in SII. The latent period of IPSPs was 1.5–6.8 msec in SI and 2.2–9.4 msec in SII. The relative importance of different pathways for excitatory and inhibitory influences of VP on SI and SII neurons is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 8, No. 2, pp. 115–121, March–April, 1976.     

Tetanus toxin conformation

Summary The circular dichroic spectrum of highly purified tetanus toxin has been determined between 200–310 nm. A comparison of the ellipticity between 207–243 nm and of the rotational strengths of the major resolved bands between 200–250 nm with the corresponding values from proteins of known conformation indicates that tetanus toxin contains about 20% -helix and 23% -structure. Above 250 nm the resolved spectrum showed contributions from tryptophanyl, tyrosyl, and phenylalanyl groups. The rotational strengths of the major near ultraviolet circular dichroic bands were significantly higher in the toxin than in low molecular weight peptides containing aromatic residues. This indicates that tetanus toxin has a stable tertiary structure.Andrew W. Mellon Foundation Teacher-Scholar Awardee.Camille and Henry Dreyfus Foundation Teacher-Scholar Awardee.     

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.     

Inhibitory effects of reticulospinal fibers of the lateral funiculus on neurons of thoracic spinal reflex pathways

Experiments on anesthetized cats with partial transection of the spinal cord showed that reticulo-spinal fibers in the ventral part of the lateral funiculus participate in the inhibition of polysynaptic reflexes evoked by stimulation of the ipsi- and contralateral reticular formation. The reticulo-fugal wave in the ventrolateral funiculus evoked comparatively short (up to 70 msec) IPSPs in some motoneurons of the internal intercostal nerve investigated and at the same time evoked prolonged (up to 500 msec) inhibition of IPSPs caused by activation of high-threshold segmental afferents. This wave also led to the appearance of IPSPs in 14 of 91 (15.5 %) thoracic spinal interneurons studied. The duration of these IPSPs did not exceed 100 msec; meanwhile, segment excitatory responses of 21 of 43 interneurons remained partly suppressed for 120–500 msec. It is concluded that the inhibitory action of the lateral reticulo-spinal system on segmental reflexes is due to several synaptic mechanisms, some of them unconnected with hyperpolarization of spinal neurons. The possible types of mechanisms of this inhibition are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 2, pp. 162–172, March–April, 1978.     

Centrifugal and centripetal connections of the cat visual cortex

In experiments on curarized cats unit responses in the dorsal lateral geniculate body to stimulation of various zones in area 17 of the visual cortex were analyzed. Of all cells tested 69% were found to respond antidromically and 8% orthodromically; in 7.6% of cells IPSPs occurred either after an initial antidromic spike or without it. The velocities of conduction of excitation along the corticopetal fibers of the optic radiation varied from 28 to 4.3 m/sec, but the three commonest groups of fibers had conduction velocities of 28–19, 14–12, and 10–9.5 m/sec. A difference between latent periods of antidromic responses of the same neurons was found to stimulation of different zones of the visual cortex; this indicates that axons of geniculo-cortical fibers split into several branches which form contacts with several neurons in area 17 of the visual cortex. The degree and possible mechanisms of cortical influences on neurons of the lateral geniculate body are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 8, No. 3, pp. 243–249, May–June, 1976.     

Correlation between pattern of synaptic effects and direction of changes in RNA content in spinal motoneurons in rats

Spinal motoneurons were activated orthodromically or antidromically with preservation of inhibitory synaptic influences (experiments on healthy rats) and after blocking these influences by tetanus toxin (experiments on rats with local tetanus). The RNA content in the cytoplasm of the -motoneurons was measured by cytospectrophotometry in UV light. The results showed no quantitative changes in the RNA of the motoneurons during action potential generation. Meanwhile the content of neuronal RNA depends on the character of synaptic influences. The RNA content in the motoneurons rises in response to excitatory and falls in response to inhibitory synaptic action. The possible mechanisms of the observed cytochemical changes in the RNA content during synaptic excitation and inhibition of motoneurons are discussed.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR. Institute of Normal and Pathological Physiology, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 4, No. 4, pp. 418–422, July–August, 1972.