Contribution of homosynaptic depression to stabilization of spinal cord potentials

The following were measured during experiments on spinal anesthetized cats: firstly, variations in the amplitude of dorsal root potentials produced by applying single or regular stimuli in 120–150 trails to hindlimb cutaneous nerves and dorsal surface of the spinal cord and secondly, numbers of extracellular discharges in neurons involved in generating these potentials. A reduction in the variation between these parameters was found when applying stimulation at the rate of 0.1–5.0 Hz. The authors attribute the effect observed to the influence of homosynaptic depression.Institute of Biology, State University Commemorating 300th Anniversary of Russian-Ukrainian Reunion, Dnepropetrovsk. Translated from Neirofiziologiya, Vol. 20, No. 2, pp. 180–185, March–April, 1988.     

Connections of the corticospinal and rubrospinal tracts with neurons of the cervical spinal cord in cats

The distribution of focal potentials over the cross section of the 7th cervical segment of the spinal cord was studied during stimulation of the pyramids, the red nucleus, and a peripheral nerve (ulnar) in adult cats anesthetized with chloralose and Nembutal. The earliest focal potentials in the fasciculus dorsolateralis were recorded 1.4–1.5 msec after stimulation of the pyramids and 0.8–0.9 msec after stimulation of the red nucleus. These times correspond to maximal condution velocities of 56–68 and 105–124 m/sec respectively. The earliest post-synaptic activity in response to pyramidal stimulation was found in the lateral areas of laminae V and VI, and in response to stimulation of the red nucleus in laminae VI and VII in Rexed's classification. The pyramidal wave also evoked considerable postsynaptic activity in medial areas of the dorsal horn. In response to stimulation of peripheral afferents activity was evoked in neurons in the central and medial parts of laminae V and VI. It is postulated on the basis of these results that corticospinal and rubrospinal fibers may be connected monosynaptically with specialized interneurons, free from peripheral influences, in the lateral areas of laminae V and VII respectively; in the lateral part of lamina VI convergence of both types of influences on the same cells is possible. Interaction between descending and afferent influences possibly takes place on more medially located neurons.A.A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 2, pp. 158–167, March–April, 1972.     

Effects of vasopressin and oxytocin on dorsal root potentials in perfused spinal cord isolated from newborn rats

Dorsal root potentials before and after adding vasopressin or oxytocin to the perfusing fluid were investigated during experiments on one or two perfused spinal cord segments isolated from 12- to 16-day-old rats. It was found that both neuropeptides reversibly inhibited the amplitude of dorsal root potentials produced by stimulating the adjoining dorsal root. The effect was dependent on concentration and time of peptide action on the brain. Both vasopressin and oxytocin were found to produce slow, reversible, dose-dependent depolarization at primary afferent fiber terminals. Depolarization persists when trans-synaptic transmission has been completely blocked owing to substitution of calcium by manganese ions in the perfusing solution. Synaptic contacts are thought to exist between peptidergic hypothalamospinal fibers and dorsal root afferent fiber terminals. The functional significance of these connections is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 20, No. 6, pp. 757–763, November–December, 1988.     

Evoked potentials in the visual and association cortex of alert cats during paired uniform stimulation of the lateral geniculate body and pulvinar

Recovery curves of evoked potentials in the association and visual cortex during paired stimulation of the pulvinar in chronic experiments on alert cats were shown to be similar in character. Depression of the test response was observed only if the interval between stimuli was of the order of 10 msec, but if it was 40 msec considerable (2–4 times) facilitation of the second response was observed, mainly on account of an increase in the negative component N₁. Facilitation was less marked if the intervals were from 60 to 100 msec, and they decreased gradually to an interval of 200 msec. The recovery curve of cortical evoked potentials during paired stimulation of the lateral geniculate body differed considerably from the recovery curve during paired stimulation of the pulvinar and was characterized by a gradual increase in amplitude of the second response — from its almost total suppression with an interval of 10 msec to slight facilitation with an interval of 200 msec. If intervals of 10 to 80 msec were used, the test response was restored more slowly in the association cortex than in the visual cortex. The results are discussed from the standpoint of differences in the character of intracortical spread of excitation as a result of activation of geniculo-cortical and pulvinar-cortical pathways of conduction of information.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 16, No. 4, pp. 497–505, July–August, 1984.     

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.     

Effect of stimulation of the caudate nucleus on activity of neurons of the globus pallidus

Activity of neurons of the globus pallidus was recorded extracellularly during stimulation of the caudate nucleus. It is demonstrated that background activity (BA) of most neurons of the globus pallidus is depressed under these conditions, which is regarded as a manifestation of inhibition of the investigated neurons. The period of BA depression varied in different cells from 60 to 500 msec. In some cases this period was preceded by emergence of an action potential with a latent period of 10–20 msec. In addition to inhibition of the activity of globus pallidus neurons during stimulation of the caudate nucleus, it was possible to record evoked responses of the given neurons in the form of group discharges with a latent period of 18–40 msec and single action potentials with a latent period of 50–100 msec. The neurons that reacted with a shorter latent period were localized at the lateral limit of the globus pallidus, whereas neurons with other kinds of responses were distributed in the globus pallidus comparatively evenly.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 1, No. 2, pp. 202–209, September–October, 1969.     

Segmental inhibitory response in the frog spinal cord during orthodromic motoneuron activation

Different types of reflex discharges were produced in various preparations by stimulating the dorsal root of isolated frog spinal cord. These ranged from multiphasic low-amplitude waves to distinctly synchronized monosynaptic response. The discharges were followed by facilitation in the former and deep, protracted inhibition of response to test dorsal root stimulation in the latter. When interstimulus intervals measured 40–50 msec, inhibitory action was less pronounced than at shorter (15–30 msec) or longer (60–100 msec) intervals, thus indicating that at least two types of inhibition were at work, one at an earlier and the other at a later stage. Strychnine at a concentration of 10^–5 M effectively reinforced the former and blocked the latter, while 10^–4 M d-tubocurarine attenuated both types of inhibition substantially. It is concluded that inhibition of response occurs mainly as a result of recurrent activation of inhibitory systems via recurrent motoneuron axon collaterals when frog spinal cord afferents are excited. Intensity of the later (presynaptic) and earlier (postsynaptic) inhibition of reflex transmission is determined by the degree of synchrony in motoneuronal discharge in response to orthodromic stimulation.Institute of Medical Radiology, Academy of Medical Sciences of the USSR, Obninsk, Kaluga Oblast. Translated from Neirofiziologiya, Vol. 19, No. 3, pp. 343–350, May–June, 1987.     

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.     

Inhibition of spinal reflex responses in the last period of embryogenesis

Some characteristics of spinal reflex reaction inhibition were studied in cat fetuses during the last three weeks of antenatal development. The experiments were conducted on fetuses with intact placental circulation. Restoration of the excitability of the spinal reflex arcs was very slow after stimulation of the dorsal root by a single stimulus. In embryos studied 20 days before birth the full inhibition of reflex responses lasted about 500 msec. Even 2–3 sec after a single stimulation of the afferent fibers the amplitude of the reflex response to the second stimulus was only 30–40% of the control value. It was determined that such long postactivation depression is unrelated to refractoriness or antidromic inhibition. The presence of a prolonged intense depolarization of afferent terminal fibers at these stages suggests a presynaptic inhibition as one of the most probable reasons for the prolonged postactivation depression. Another important factor in the appearance of postactivation depression is probably the morphologic and functional immaturity of synaptic structures. A reciprocal inhibition was observed in cat fetuses on the 10–12th antenatal day. On the basis of these data it is suggested that in embryogenesis presynaptic inhibition considerably precedes that of postsynaptic fibers.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 3, No. 1, pp. 68–75, January–February, 1971.     

Nonadrenergic inhibitory postsynaptic potentials of gastric smooth muscle cells

Single intramural stimulation of the atropinized muscle strip of the guinea pig stomach by square pulses was accompanied by the formation of inhibitory postsynaptic potentials (IPSPs) in the muscle cells and by relaxation of the strip. The mean latent period of the IPSPs was 150±15 msec, and the time for its amplitude to rise and fall was 150±15 and 375±92 msec respectively. The latent period of the onset of relaxation of the muscle strip was 1850±230 msec. The amplitude and rate of rise of these IPSPs increased with an increase in the strength of stimulation. This shows that the same gastric muscle cell is under the inhibitory influence not of one, but of several nerve fibers. The effectiveness of synaptic transmission was largely dependent on the character of the preceeding stimulation. For instance, in response to repeated stimulation with short intervals facilitation was observed, but after repetitive stimulation had ended posttetanic depression followed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 2, pp. 216–222, March–April, 1972.     

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.     

Postnatal changes in the dorsal root reflex in the isolated spinal cord of the hamster,Mesocricetus auratus

Spontaneous activity has been demonstrated in the lumbar dorsal roots of isolated spinal cord preparations taken from animals ranging in age from 2 to 65 days. Peaks of activity were recorded at 2 and 5 weeks of age, with mean firing frequencies of 33 Hz and 28 Hz respectively. The firing frequency in weeks 3 and 4 was lower (15 Hz) as was the frequency in cords taken from animals older than 6 weeks. The pattern of the spontaneous dorsal root activity changed during the first 5 weeks of life. In cords taken from animals less than 10 days old, the roots fired single action potentials, producing a single broad peak in Inter Spike Interval plots (ISI). Dorsal root recordings made from cords taken from animals in weeks 2 and 3 of life exhibited both single spikes and bursts of action potentials. By the end of the third week of life, individual spike activityhad declined and the bursts of action potentials characteristic of the adult pattern had become dominant, producing a bimodal ISI plot. Cross correlation analysis of dorsal root and dorsal horn activity in lumbar segments up to five segments apart, revealed an increasing degree of correlation developing over the first 4 weeks of postnatal life. Dorsal horn responses to dorsal root stimulation in cords taken from young animals were prolonged, lasting in excess of 250 msec. In the third week of life, the duration of the excitatory component of the response was reduced to approximately 50 msec by the development of an inhibitory phase.     

Functional development of hippocampal mossy fiber synapses in rabbits

The course of functional maturation with age of mossy fiber synapses on pyramidal cells in areas CA_3,4 of the dorsal hippocampus was investigated by extracellular recording of focal potentials and single unit responses of the hippocampus to electrical stimulation of the dentate fascia in waking, unimmobilized rabbits aged from 1 to 14 days. After the 4th day of postnatal life focal potentials appeared in response to single stimulation, in the form of a biphasic short-latency wave, characteristic of responses of the mature hippocampus, accompanied by spike discharges with a latent period of 3 to 10 msec and inhibitory responses of the hippocampal neurons. During the next 10 days the amplitude of the focal potentials increased from several hundred millivolts, with the sharpest increase observed from the 4th through the 7th days. In early age periods global and unitary responses were shown to be capable of frequency potentiation and also of short-term after-potentiation.Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 12, No. 3, pp. 246–254, May–June, 1980.     

Investigation of the stability of the potentials of the dorsal surface evoked by single and paired stimulations of the afferent nerve

In spinal and anesthetized cats in the region of the lumbosacral thickening we have recorded the potentials of the dorsal surface (PDS) in response to single or paired stimulation of the peripheral nerves. The intervals between the stimuli were 400, 100, and 20 msec. The recording was made once every 15 sec. We have constructed the histograms of the changes in the N₁-component recorded on conditioning and single stimulation. After conversion of the histograms for single responses we established agreement of the newly obtained histograms with those constructed for the conditioned responses. The coefficients of variance for both cases proved to be practically identical. In applying single stimulation of different strengths the coefficient of variance increased if the amplitude of the responses fell. The coefficient of variance for the low amplitude responses did not change on conditioning unlike that for the responses evoked by weak single stimulation. It has been shown that the confidence limits of change in the coefficient of variance for a confidence probability of 0.99 and 0.95 obtained in experiments with conditioning practically concur with the intervals for the single stimulation. It is concluded that presynaptic inhibition has no appreciable antifluctuation influences on the N₁-component of the PDS.Dnepropetrovsk State University. Translated from Neirofiziologiya, Vol. 2, No. 1, pp. 10–16, January–February, 1970.     

Responses of units in the magnocellular part of the medial geniculate body to acoustic and somatosensory stimulation

Responses of 150 neurons in the magnocellular part of the medial geniculate body to clicks and to electrodermal stimulation of the contralateral forelimb were investigated in cats immobilized with myorelaxin. Of the total number of neurons 65% were bimodal, 16.6% responded only to clicks, and 15.4% only to electrodermal stimulation. The unitary responses were excitatory (spike potentials) and inhibitory (inhibition of spontaneous activity). Responses beginning with excitation occurred more frequently to stimulation by clicks than to electrodermal stimulation, whereas initial inhibition occurred more often to electrodermal stimulation. The latent period of the initial spike potentials in response to clicks and to electrodermal stimulation was 5–27 and 6–33 (mean 11.6 and 16.2) msec respectively. Positive correlation was found between the latent periods of spike potentials recorded in the same neurons in response to clicks and to electrodermal stimulation, and also to electrodermal stimulation and to stimulation of the dorsal funiculus of the spinal cord. It is concluded that the magnocellular division of the medial genicculate body is a transitional structure between the posterior ventral nucleus and the parvocellular division of the medial geniculate body, and that in addition, it is connected more closely with the auditory than with the somatosensory system. It is suggested that the somatosensory input into the magnocellular division of the medial geniculate body is formed mainly by fibers of the medial lemniscus.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 2, pp. 133–141, March–April, 1978.     

Synaptic processes in the neurons of Clarke's column evoked by an antidromic volley from the dorsolateral column

In cats under nembutal-chloralose anaesthesia we investigated the response of neurons of Clarke's column to stimulation of axons ascending in the dorsal part of the lateral funiculus. Excitation of the descending fibers of the funiculus was prevented either by an ipsilateral hemisection of the thoracic cord carried out 7–10 days previously, which caused them to degenerate, or by stimulation of ascending axons in the region of the restiform bodies. It was found that with both kinds of stimulation records could be obtained from neurons in Clarke's column in which a descending volley causes not antidromic action potentials but primary excitatory postsynaptic potentials (EPSP). The length of the latent period of the EPSP (10–15 msec) suggests that they are monosynaptic. Such neurons may also be activated by low- or high-threshold afferents from various muscles; evidently they correspond to those described by Retheyi [14] as "edge" neurons on which terminate collaterals of axons ascending in the dorsal spinocerebellar tract (DSCT). In some of the neurons of the DSCT whose axons are distinguished by a low conduction velocity, stimulation of the dorsolateral funiculus caused not only antidromic spikes but also EPSP's following after them, and it would seem that the "edge" neurons were involved in their formation. We consider the possible functional role of a negative feed back loop formed by axon collaterals of neurons of the DSCT and by the "edge" neurons.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 2, No. 3, pp. 269–278, May–June, 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.     

Dynamic characteristics of motor responses evoked by stimulation of the motor cortex in unanesthetized cats

Temporal characteristics of motor responses evoked in unanesthetized cats by stimulation of the motor cortex through bipolar needle electrodes were investigated in chronic experiments. Isometric and isotonic contractions of the flexor muscles of the hip and knee joints of the limb contralateral to the point of stimulation were recorded. The latent period of response varied from 100 msec or more in the case of low-frequency (100–150 Hz) and low-threshold (1.1–1.2 thresholds) stimulation of the motor cortex to 30–35 msec in the case of "optimal" parameters of stimulation (300–400 Hz, 1.5–1.6 thresholds). If the intensity of stimulation was high enough the rising time constant of evoked contraction was 50–80 msec; values of the falling time constant of muscular contraction after cessation of stimulation were much greater, namely 150–300 msec. The rising time constant of contraction decreased with an increase in both the frequency and strength of motor cortical stimulation. The results are examined and discussed from the standpoint of methods of automatic control theory.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 5, pp. 451–458, September–October, 1980.     

Responses of the cingulate cortex to dorsal hippocampal stimulation in cats

Responses of the cingulate gyrus to stimulation of the dorsal hippocampus were studied in unanesthetized cats. Both short and long polysynaptic projections were found to participate in their genesis. It is postulated on the basis of the results of experiments with stimulation of and injury to the limbic nuclei of the thalamus that responses of the posterior zone of the cingulate gyrus to dorsal hippocampal stimulation arise as a result of activation of the anteroventral thalamic nucleus.I. S. Beritashvili Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 13, No. 1, pp. 7–13, January–February, 1981.     

Electrophysiological study of connections between the entorhinal cortex and the neocortex

In acute experiments in rabbits immobilized by d-tubocurarine, stimulation of the entorhinal area with rectangular electric impulses led to the appearance of evoked potentials (EP) with a latent period of 6–12 msec in the occipital, temporal, parietal, and cingular areas of the neocortex. The amplitude of the positive response component was 500 µV, and its duration 25–50 msec. The negative component was not always discernible. When rhythmic stimulation was used, these EPs followed stimulation frequencies not exceeding 20 per sec. Stimulation of the medial parts of the entorhinal area with a frequency of one to three per sec was accompanied by recruitment of the EP in the occipital and temporal neocortex areas. Nembutal depressed the amplitude of the neocortex EP appearing in response to stimulation of the entorhinal cortex. With the aid of double stimulation it could be established that, after conditioning stimulation of the entorhinal area, the positive component of the primary response (PR) evoked by stimulation of the contralateral sciatic nerve in the projection zone of the somatosensory cortex is strengthened during the first 50 msec, and subsequently after 80–120 msec. In these cases, the negative component was depressed. These findings are discussed with a view to the influence of limbic structures on the neocortex.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 2, No. 1, pp. 73–78, January–February, 1970.