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.     

Distribution of terminals of primary afferent fibers connected polysynaptically with motoneurons in the frog spinal cord

Parallel intracellular recordings of potentials in primary afferent fibers (in the region of their entry into the spinal cord) and motoneurons were made in experiments on an isolated perfused preparation of frog spinal cord preserving its connections with hind limb nerves. It was shown by injection of horseradish peroxidase through a microelectrode inserted into the fiber that fast-conducting cutaneous, tendon, and muscular afferents connected polysynaptically with motoneurons reach only the upper or middle third of the dorsal horn. Terminal branches of these fibers are characterized by numerous short terminal twigs given off at short distances apart from larger collaterals. Terminal boutons and en passant contacts, stained with horseradish peroxidase, were found on bodies of interneurons. In some cases, trans-synaptic staining of interneurons was found to take place. It is suggested that peroxidase-labeled interneurons form axo-axonal synapses with primary afferents.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 14, No. 6, pp. 615–621, November–December, 1982.     

Synaptic activation of thoracic interneurons by reticulospinal fibers of the lateral funiculus

Synaptic responses of different functional groups of interneurons in segments T10 and T11 to stimulation of the ipsilateral and contralateral medullary reticular formation were investigated in anesthetized cats with only the ipsilateral lateral funiculus remaining intact. Activation of reticulospinal fibers of the lateral funiculus with conduction velocities of 30–100 m/sec was shown to induce short-latency and, in particular, monosynptic EPSPs in all types of cells tested: in interneurons excited by group Ia muscle afferents, in cells activated only by high-threshold cutaneous and muscle afferents (afferents of the flexor reflex), in cells activated mainly by descending systems, and, to a lesser degree, in neurons connected with low-threshold cutaneous afferents. These cell populations are located mainly in the central and lateral parts of Rexed's lamina VII. Most neurons in laminae I–V of the dorsal horn, except six cells located in the superficial layers of the dorsal horn, received no reticulofugal influences. The functional organization of connections of the lateral reticulospinal tract with spinal neurons is discussed and compared with the analogous organization of the medial reticulospinal tract, and also of the "lateral" (cortico- and rubrospinal) descending systems.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 2, pp. 150–161, March–April, 1978.     

Effect of serotonin on neuronal background activity in a hemisegment isolated from the infant rat spinal cord

Neuronal background activity was investigated in a hemisegment of the lumbar section of the spinal cord before and after addition of serotonin (5-HT — 1 × 10^–8–10^–4 M) in 14- to 22-day-old rats. Reversible changes in background firing rate were recorded in 50% and 70.6% of dorsal and ventral horn interneurons respectively. Excitatory response predominated; in the dorsal horn, 62.4% of all cells responding to 5-HT showed an excitatory response, 8.4% an inhibitory reaction, and 29.2% a two-stage response. In the ventral horn, an excitatory and two-stage response were recorded in 91.6% and 8.4% of cells respectively. Application of 5-HT induced an increase in firing rate and depolarization in the ventral horn. Findings from this study would point to a primarily excitatory effect of 5-HT on background in segmental neurons.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 3, pp. 335–343, May–June, 1989.     

Presynaptic inhibition of segmental interneurons

In experiments on spinal cats changes in the second negative postsynaptic component (N₂) of the dorsal surface potential (DSP) of the spinal cord recorded in the region of segment L7 was used as the index of inhibition of segmental dorsal horn interneurons. Conditioning and testing stimuli were applied at increasing time intervals to the popliteal and superficial peroneal nerves respectively. Changes in the N₂ component were compared with changes in the N₁ component of the DSP, reflecting mainly activity of nonsegmental ascending dorsal horn interneurons. After an initial short facilitation a conditioning volley of pulses evokes prolonged (over 500 msec) inhibition of the N₂ component, characterized by the presence of two maxima (on the average at the 16th and 80th milliseconds) which indicate that two systems with different latent periods play a role in this inhibition. In its shape and temporal characteristics the curve of inhibition of the N₂ component corresponds to the two-component dorsal root potential (DRP) recorded in spinal animals in response to stimulation of flexor afferents (FRA) [8, 19]. Together with other features, this similarity is evidence of the presynaptic nature of this inhibition. Intravenous injection of hexobarbital has a stronger action on inhibition of the N₂ component, leading to a marked increase in its depth and duration. Suggestions are made regarding the functional organization of systems responsible for presynaptic inhibition of segmental dorsal horn interneurons.Deceased.Dnepropetrovsk State University. Translated from Neirofiziolgiya, Vol. 4, No. 1, pp. 75–82, January–February, 1972.     

Pyramidal influences on interneurons of spinal segmentary reflector arcs in cat

Microelectrode discharges of potentials have been realized from segmentary interneurons of the dorsal horn and intermediate nucleus of the spinal cord in cat at the L₆–L₇ level by electrical stimulation of the sensorimotor region of the brain cortex. It has been established that corticifugal influences on segmentary interneurons of the system of the flexor reflex and on neurons activated by high threshold muscle afferents (groups Ib, II, and III), or high threshold cutaneous afferents are predominantly excitatory. Interneurons activated by muscle afferents of group Ia or by the lowest threshold cutaneous fibers are weakly subjected to pyramidal influences. The mean latencies of excitatory postsynaptic potentials (EPSP's) and discharges evoked under the influence of pyramidal volley, for the neurons under study in the system of afferents of the flexor reflex are equal to 11.8±2.6 and 20.1±1.8 msec, respectively; for interneurons, excited only by high threshold muscle afferents, they are equal to 15.5±3.6 and 16.3±2.2 msec, respectively; and for interneurons, excited by high threshold cutaneous fibers they are equal to 11.8±2.6 and 18.3±1.4 msec, respectively. Possible pathways of activating segmentary interneurons from the lateral sensorimotor region of the brain cortex have been discussed.The A. A. Bogomolets Institute of Physiology, Academy of Sciences, Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 2, No. 1, pp. 17–25, January–February, 1970.     

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

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

Synaptic activation of thoracic spinal interneurons by reticulospinal pathways

Synaptic processes of 119 thoracic spinal interneurons (T10–11) were investigated in anesthetized cats in response to stimulation of the medial and central zones of the gigantocellular nucleus in the medulla and the ventral columns of the spinal cord. Fast (90–130 m/sec) reticulospinal fibers running in the ventral column were found to produce monosynaptic or disynaptic excitation of interneurons of Rexed's layers VII–VIII, which are connected monosynaptically with group I muscle afferents, and interneurons excited both by group I muscle afferents and low-threshold cutaneous afferents. In most neurons of layer IV, connected monosynaptically with low-threshold cutaneous afferents, and in neurons of layers VII–VIII excited by afferents of the flexor reflex no marked postsynaptic processes were observed during stimulation of the reticular formation. Excitatory, inhibitory, and mixed PS Ps during activation of reticulospinal fibers were found in 14 neurons, high-threshold afferents in which evoked predominantly polysynaptic IPSPs. Seventeen neurons activated monosynaptically by reticulospinal fibers and not responding to stimulation of segmental afferents were found in the medial part of the ventral horn (layers VII–VIII).A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 6, pp. 566–578, November–December, 1972.     

Fos Protein Expression in Sacral Spinal Cord in Relation to Early Phase of Cauda Equina Syndrome in Dogs

1. The aim of the present study is to map the incipient phase of Fos expression in the sacral spinal cord neuronal pools of multiple cauda equina constrictions canine model.2. Fos-positive neurons were found bilaterally in the lateral portion of superficial dorsal horn layers (Laminae I–III) and along the lateral edge of the dorsal horn accompanied by the lateral collateral pathway, fibers of Lissauer's tract, terminating at the sacral parasympathetic nucleus. Similarly, high Fos expression was detected in the ventral portion of the dorsal sacral commissure and in the dorsomedial portion of the anterior horns at S₁–S₃ segment level. Finally, a clearly expressed Fos-positivity was disclosed bilaterally in the neuropil of the nucleus Y in the anterior horn.3. Data from the present study show that continuous stimulation of the central fibers of sacral dorsal root ganglia neurons, i.e., fibers of sacral primary afferents, unlike those using various stimulations of the peripheral fibres offers an unusual pattern of Fos-like immunoreactivity.     

Reticulofugal influences of interneurons in the lateral region of gray matter of the cat spinal cord

Responses of lumbar interneurons located in the most lateral regions of Rexed's laminae IV–VII to stimulation of the medial longitudinal bundle and gigantocellular reticular nucleus of medullary pyramids, red nucleus, and peripheral nerves were investigated in cats anesthetized with pentobarbital. Stimulation of the reticulospinal fibers evoked monosynaptic excitation of many interneurons specialized for transmitting activity of the lateral descending systems, but not of peripheral afferents. Convergence of excitatory influences of all three descending systems (cortico-, rubro-, and reticulospinal) was observed on some cells of this group. In addition, monosynaptic "reticular" E PSPs appeared in interneurons transmitting activity of group Ia muscle fibers and in some interneurons of the flexor reflex afferent system. Stimulation of reticulospinal fibers evoked IPSPs in some neurons of this last group. Neurons not exposed to reticulofugal influences (both specialized neurons and interneurons of segmental reflex arcs) were located chiefly in the dorsal zones of the region studied. Recordings were also obtained from single fibers of the lateral reticulospinal tracts (conduction velocity from 26 to 81 m/sec).A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 5, No. 5, pp. 525–536, September–October, 1973.     

On mechanisms of depression in pathways of presynaptic inhibition

We investigated inhibition of the N₁-component of the spinal cord dorsal potential (CDP) evoked by experimental stimulation of the n. peroneus in spinal cats. Stimulation was carried out following two conditioning stimuli administered at different time intervals to the same or different cutaneous nerves. The interval between the last conditioning stimulus and the experimental one remained constant (20 msec). It is demonstrated that there is no dependence between weakening of inhibitory action of the second conditioning stimulus and inhibition of the dorsal horn interneurons excited by it that generate the N₁-component of the CDP. It is hypothesized that mechanisms which act on the principle of negative feedback are present in the vincinity of the synaptic junctions of cutaneous afferent fibers with neurons of the substantia gelationsa, and that these mechanisms restrict the development of presynaptic inhibition during inflow of a series of afferent impulses into the cord.Dnepropetrovsk State University. Translated from Neirofiziologia, Vol. 1, No. 3, pp. 253–261, November–December, 1969.     

脊髓背角痛觉传递和调制的一些化学解剖学观察

本实验研究了脊髓背角内Ｃ纤维末梢的分布和突触学特征及其一些神经递质化学构筑;定量观察了急性痛引起背角的递质变化;显示了初级传入Ｃ纤维,抑制性中间神经元和背角伤害性感受神经元三者之间的突触关系,并探讨它们在痛觉信息传递和调制中的作用。     

Synaptic processes in neurons of the cervical enlargement of the cat spinal cord during stimulation of propriospinal pathways of the dorsolateral tract

Responses of motoneurons and interneurons of the cervical enlargement of the cat spinal cord were studied by a microelectrode technique during selective stimulation of propriospinal fibers of the dorsolateral tract of the lateral white column. The long descending and ascending pathways were blocked by preliminary (10–16 days earlier) hemisection of the spinal cord cranially and caudally to the segments studied. Stimulation of the dorsolateral tract at a distance of 15–25 mm from the site of recording evoked complex postsynaptic potentials consisting of several successive waves in the motoneurons. The character of the PSPs was not clearly linked with the function of the motoneurons. By their latent periods the components of the PSPs could be placed in three groups. The "primary" components were reproduced in response to stimulation at 50–100/sec whereas the "secondary" and "tertiary" components were weakened or blocked. It is postulated that the "primary" components are evoked through monosynaptic connections between propriospinal fibers of the dorsolateral tract and motoneurons of the forelimb muscles, while the late components are evoked through polysynaptic pathways, including segmental interneurons. Many of these interneurons, located in the ventral horn and intermediate zone, were strongly excited during stimulation of the dorsolateral tract.A. A. Bogomolets' Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 5, No. 1, pp. 61–69, January–February, 1973.     

Experimental morphological study of primary afferent terminals at the base of the dorsal horn of the cat spinal cord

The distribution and ultrastructure of primary afferent terminals in the gray matter of the cervical and lumbar regions of the cat spinal cord were studied by the experimental degeneration method of Fink and Heimer. Most preterminals of primary afferents were shown to be concentrated in the region of the intermediate nucleus of Cajal (central part of Rexed's laminae VI–VII), in the substantial gelatinosa (laminae II–III), and in the nucleus proprius of the dorsal horn (central and medial parts of lamina IV). Fewer are found in the region of the motor nuclei. The number of degenerating axon terminals in the lateral parts of laminae IV and V differed: 31.5 and 0.4% respectively of all axon terminals. Many terminals of primary afferents in lamina IV contribute to the formation of glomerular structures in which they exist as terminals of S-type forming axo-axonal connections with other terminals. These results are in agreement with electrophysiological data to show that interneurons in different parts of the base of the dorsal horn differ significantly in the relative numbers of synaptic inputs formed by peripheral afferents and descending systems.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 5, No. 4, pp. 406–414, July–August, 1973.     

Effects of dopamine on background and evoked activity in interneurons of a spinal cord segment isolated from infant rats

The effects of 1·10^–5–1·10^–3 M dopamine on background and evoked interneuronal-activity was investigated during experiments on a spinal cord segment isolated from 11–18-day old infnat rats. Dopamine induced an increase in background firing activity rate in 52.5% and a reduced rate in 42.5% of the total sample of responding cells. Dopamine exerted a primarily inhibitory effect on interneuronal activity invoked by dorsal root stimulation, as witnessed by the reduced amplitude of the postsynaptic component of field potentials in the dorsal horn together with the fact that invoked activity was depressed in 66.7% of total interneurons responding to dopamine and facilitated in only 33.3% of these cells. All dopamine-induced effects were reversible and dose-dependent. Dopamine-induced effects disappeared after superfusing the brain with a solution containing 0–0.1 mM Ca²⁺ and 2 mM Mn²⁺, suggesting that this response is of transsynaptic origin. In other cells the excitatory or inhibitory action of dopamine also persisted in a medium blocking synaptic transmission; this would indicate the possibility of dopamine exerting depolarizing and hyperpolarizing effects on the interneuron membrane directly. Contrasting responses to dopamine in interneurons may be attributed to the presence of different types of dopamine receptors in the spinal cord.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 1, pp. 7–16, January–February, 1989.     

QUANTITATIVE HISTOCHEMISTRY OF γ-AMINOBUTYRIC ACID IN CAT SPINAL CORD WITH SPECIAL REFERENCE TO PRESYNAPTIC INHIBITION

Abstract— A method is described for quantifying the GABA distribution in cat spinal cord at 200–500 μn resolution. Isolated spinal cord (L5–S1) was frozen and sectioned at about 150 μm thickness. The frozen tissue section was cut into 200 or 500 μm square blocks. The GABA content of each square tissue block was determined by enzymic micromethods and GABA distribution was mapped quantitatively. Average GABA concentrations were: 0·4 mmol/l. in white matter, 1·2 mmol/l. in ventral horn and 1·7 mmol/l. in dorsal horn. The highest concentrations of GABA (2–3 mmol/l.) were found in the dorsolateral part of dorsal horn. In order to destroy the interneurons of dorsal horn, the blood vessels supplying the dorsal horn of the lumbar enlargement were unilaterally cauterized. Seven to 30 days after operation, both the size of dorsal root potential and the GABA level in the dorsal horn were markedly reduced on the cauterized side. These results suggest that GABA is highly concentrated in the interneurons of dorsal horn and functions as a transmitter of presynaptic inhibition.     

Synaptic processes in spinal cord interneurons under rubrospinal effects

Synaptic processes of the spinal cord interneurons under rubrospinal effects have been investigated. A recording was made of 156 interneurons from the different parts of the gray matter, 111 of the interneurons were activated by descending effects from the red nucleus and 47 were not activated. Sixty nine interneurons of the first group responded only to rubrospinal impulsation and 42 neurons were also activated by afferent volleys. Interneurons activated only by the rubrospinal tract were located in the most lateral part of the VII Rexed's gray matter layer; the majority of interneurons activated by both rubrospinal and peripheral afferent volleys were located in the nucleus propius of the dorsal horn and the Cajal intermediate nucleus. The mean latencies of EPSP's and action potentials in interneurons activated only by a rubrospinal tract were 64±0.2 and 9.5±0.62 msec, respectively. The mean latency of EPSP's in motoneurons of flexor muscles was 10.3±0.62 msec and of IPSP's in motoneurons of extensor muscles, it was 11.5±1.28 msec. It is assumed that rubrospinal impulsation evokes excitatory PSP's in the motoneurons via the disynaptic pathway with the participation of special interneurons located in the lateral part of the VII layer. Inhibitory and late excitatory responses are, apparently, evoked via additional interneurons.A. A. Bogomolets Institute of Physiology of the Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 1, No. 2, pp. 158–166, September–October, 1969.     

Effects of dexamethasone on the electrical activity of spinal neurons in rats with the transected sciatic nerve

Effects of the glucocorticoid hormone dexamethasone on the reflex discharges in the lumbar ventral roots and background activity (BA) of single neurons in the dorsal laminae of spinal grey were studied in rats after transection of the sciatic nerve. Administration of the hormone during early post-traumatic period (up to seven days) evoked no significant changes in the amplitude of increased (due to the postdenervation hyperreflexia) monosynaptic discharges on the side of nerve transection. At the same time, the monosynaptic discharges grew by 150–170% on the intact side. During later post-transection periods (up to 35 days), when ventral root reflex discharges were suppressed, dexamethasone facilitated reflex transmission via the polysynaptic segmental pathways on both the operated and intact sides. Nonetheless, the monosynaptic component of reflex discharges on the injured side did not recover. Dexamethasone treatment resulted in an increase in the number of BA-generating interneurons within the superficial dorsal horn laminae, and in a decrease in the proportion of units generating bursting activity (possibly of pathological nature).Neirofiziologiya/Neurophysiology, Vol. 27, No. 1, pp. 26–31, January–February, 1995.     

Spinal control of afferent temperature information in the cat

The effect of picrotoxin (at sub-convulsant doses, i.v.) on the background and invoked spike activity of cat dorsal horn internerons was investigated while thermal and mechanical influences were at work on the skin receptor areas. It was found that information on skin temperature is modulated at the presynaptic level and largely mediated by competitive interaction between large and small diameter fibers.Institute of Physiology, Academy of Sciences of the Kazakh SSR, Alma Ata. Translated from Neirofiziologiya, Vol. 18, No. 6, pp. 773–779, November–December, 1986.     

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.