Effects of tractotomy on reflex activity in the lumbar segment of the rat spinal cord previously disrupted by severing the sciatic nerve

Evoked electrical discharges in the spinal cord roots and dorsal surface ipsilateral to the previously severed sciatic nerve (as well as on the contralateral side) were investigated in rats one, three, seven, and 14 days after tractotomy. Monosynaptic reflex discharges in the ventral roots were found to return to 20–40% of the level of this parameter as measured on the contralateral side within seven and 14 days after tractotomy. Mean amplitude of antidromic dorsal root discharges, afferent peak, and the N₁ component of potential(s) at the dorsal surface ipsilateral to the severed nerve barely altered, remaining significantly lower than on the contralateral side. Mechanisms are suggested for the increase in monosynaptic reflex ventral root discharges ipsilateral to the severed nerve following tractotomy — thought to be largely due to raised sensitivity to transmitter at the motoneuronal membrane resulting from degeneration of synapses of descending pathways.Medical Institute of the Ukrainian Ministry of Health, Dnepropetrovsk. Translated from Neirofiziologiya, Vol. 21, No. 3, pp. 366–371, May–June, 1989.     

Dynamics of post-denervational modifications of spinal reflex activity in albino rats

In experiments on rats, we studied the characteristics of reflex discharges in the ventral root (VR) L ₅; the discharges were evoked by stimulation of segmental (peripheral nerve or dorsal root, DR) and suprasegmental vestibular (stimulation of the round window of the labyrinth) inputs. Potentials were recorded within different time intervals (from 1 to 150 days) after transection of the sciatic nerve (SN); measures preventing regeneration of its fibers were used. Modifications of the segmental responses related to post-denervational changes included four phases: (i) latent period, (ii) post-denervational spinal hyperreflexia (PDSH), (iii) partial suppression of monosynaptic discharges (MDs) in the VR, and (iv) complete disappearance of VR MDs resulting from late post-denervational changes. The latency of post-denervational modifications was about 18–48 h after the moment of transection of the SN. Within the PDSH phase, modifications were the greatest 3 to 5 days after transection; these changes could be more adequately estimated in the case of stimulation of the DR on the side of transection and not under conditions of stimulation of the central segment of the transected SN per se. Within this phase, the amplitudes of VR MDs and responses to vestibular stimulation were augmented two to three and four to five times, as compared with the respective indices in intact animals. From the 7th to 10th day after the nerve transection, the amplitude of VR MDs progressively dropped, and on about the 20th day these discharges practically disappeared, while polysynaptic components of segmental responses were preserved. Vestibular responses within this period were, as earlier, considerably facilitated. On the 60th and 150th days (within the phase of late post-denervational modifications) there were no VR MDs after stimulation of segmental inputs, and polysynaptic responses were exclusively observed. The amplitude of discharges evoked by vestibular stimulation became lower than in the PDSH state but remained significantly higher than the control values of this parameter. Probable mechanisms of post-denervational modifications of the evoked spinal activity within different time intervals after transection of the SN are discussed. Neirofiziologiya/Neurophysiology, Vol. 39, No. 1, pp. 37–46, January–February, 2007.     

Potential role of altered calcium conductance at the onset of intensified spinal reflex after severing the sciatic nerve

The action of substances either increasing or inducing penetration of calcium ions through neuronal membranes on monosynaptic reflex discharges in the ventral horns (MR VH) were investigated in white rats between 5 and 7 days after severing the sciatic nerve. Systemically administered imidazole and 4-aminopyridine were used for the former and verapamil for the latter purposes. Effects of denervation and either imidazole or 4-aminopyridine administration were found to be synergistic; these interventions all led to a considerable increase in MR VH. Verapamil, on the other hand, reduced MR VH amplitude and raised the threshold for triggering these on both the operated and contralateral side. It is suggested that the early intensification of MR VH after severing the nerve is partly due to increased voltage-dependent calcium currents resulting from a reduced cyclic adenosine monophosphate level at presynaptic terminals of the reflex arc investigated.Medical Institute, Ministry of Public Health, Dnepropetrovsk. Translated from Neirofiziologiya, Vol. 22, No. 6, pp. 826–832, November–December, 1990.     

Peculiarities of spinal hyperreflexia after combined synchronous transection of the sciatic nerve and chordotomy in rats

Parameters of the reflex discharges evoked by spinal dorsal root stimulation were measured in rats with the sciatic nerve and spinal cord (at low thorasic level) transected five days earlier. Monosynaptic discharges in the ventral roots were found to increase after the operation; the degree of increase was significantly higher as compared with that observed after isolated transections of the spinal cord or the nerve. The combined lesion of the nerve and spinal cord could result in the appearance of high-amplitude reflex discharge components, probably of a polysynaptic nature. We concluded, from the comparison of modifications of reflex discharges, that the mechanisms underlying spinal hyperreflexia after nerve or spinal cord lesions differ considerably from each other.Neirofiziologiya/Neurophysiology, Vol. 26, No. 3, pp. 197–202, May–June, 1994.     

Cholinergic modulation of the synaptic transmission in the frog spinal cord

It was found during experiments on isolated frog spinal cord involving extracellular recording from the dorsal roots (sucrose bridging) and intracellular recording from motoneurons by microelectrodes that 10 mM of the M-cholinomimetic arecoline produces motoneuronal depolarization which is matched by depolarizing electronic ventral root potentials and a rise in motoneuronal input resistance. Arecoline changes synaptic transmission by increasing the amplitude of postsynaptic potentials during intracellular recording and that of motoneuronal reflex discharges in the ventral roots but reduces the duration of dorsal root potentials. In the presence of arecoline, L-glutamate-induced motoneuronal response increases. Facilitation of synaptic transmission produced by arecoline in the spinal cord is bound up with cholinergic M₂- activation, since it is suppressed by atropine but not by low concentrations of pirenzipine; it is also coupled with a reduction in adenylcyclase activity. When motoneuronal postsynaptic response has been suppressed, as in the case of surplus calcium or theophylline, arecoline produces an inhibitory effect on the amplitude of motoneuronal monosynaptic reflex discharges which is suppressed by pirenzipine at a concentration of 1×10^–7 M. This would indicate the presence at the primary afferent terminals of presynaptic cholinergic M₁ receptors which mediate its inhibition of impulses of transmitter release. This effect is independent of changes in cyclic nucleotide concentration.A. M. Gorkii Medical Institute, Donetsk. Translated from Neirofiziologiya, Vol. 19, No. 3, pp. 399–405, May–June, 1987.     

Aspects of segmental reflex after damage of the sciatic nerve in thyroxin-treated rats

In experiments on spinalized rats, in whom the sciatic nerve was severed three weeks before, and which were given thyroxin (100 µg/kg) for three days before the acute experiment, the amplitude of the reflex firing in the ventral horn (RFVH) of segment L₅ was recorded when the dorsal horn was stimulated before and 20 min after the intraperitoneal administration of obsidan, clofelin, and finoptin. It was found that obsidan did not alter, while clofelin and finoptin mainly reduced the amplitude of the monosynaptic component of the RFVH, which was restored under the influence of thyroxin on the side of the operation.Dnepropetrovsk Medical Institute, Ukrainian Ministry of Health. Translated from Neirofiziologiya, Vol. 24, No. 6, pp. 653–659, November–December, 1992.     

Effect of noradrenalin and serotonin on synaptic transmission in the rat spinal cord

Experiments on superfused isolated spinal cord preparations from rats aged 8–13 days showed that noradrenal in and serotonin have only a weak effect on monosynaptic reflex discharges but a substantial effect on polysynaptic motoneuronal discharges: noradrenalin potentiates whereas serotonin inhibits them. Both amines inhibit dorsal root potentials evoked by stimulation of high-threshold afferents. Potentiation of polysynaptic motoneuronal discharges induced by noradrenalin is connected with hyperpolarization of high-threshold afferents due to inhibition of the function of neurons in the substantia gelatinosa, and with increased excitability of interneurons participating in the generation of motoneuronal discharges. Serotonin inhibits polysynaptic motoneuronal discharges through its direct depolarizing effect on terminals of high-threshold afferents and depression of interneuron activity responsible for these discharges. Adrenergic and serotonin receptors, mediating these effects of noradrenalin and serotonin, were subjected to pharmacologic analysis.A. M. Gor'kii Donetsk Medical Institute. Translated from Neirofiziologiya, Vol. 14, No. 3, pp. 241–247, May–June, 1982.     

Effect of axotomy on cholinergic enzyme activities in the spinal cord and sciatic nerve of the dog

Choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activity measured in the ventral and dorsal part of the dog spinal cord (L6-S2) and in the stumps of the sciatic nerve 5, 10, 15 and 21 days after its transection were compared with the corresponding activities in the intact contralateral nerve and in sham-operated animals. AChE was also examined histochemically. Changes in the enzyme activities in the central nerve stump were correlated with activity changes in the spinal cord. In the central nerve stump, a marked (25%) increase in AChE activity was found on the fifth day after transection, but by the 21st day it fell below control value levels; up to the 15th day it showed good correlation with AChE activity in the ventral spinal cord. Histochemically, pronounced reduction of enzymatic activity was found in the ipsilateral part of the spinal cord. On the 15th day, ChAT activity in the ventral spinal cord was also significantly decreased and the accumulation of the enzyme in the central nerve stump was negligible. On the contrary, at the last 21-day interval examined, a significant increase in ChAT activity and a nonsignificant increase in AChE activity was found in the spinal cord, but their activities in the central nerve stump were decreased. In the degenerated peripheral nerve stump ChAT activity dropped by an average of 99% and AChE activity by 48% during the first 15 days after transection but, on the 21st day, AChE activity was 22% higher than at the preceding interval.     

Extrapyramidal descending influences on neurons of the spinal cord in a superreflexia state

The spinal superreflexia state was modeled in experiments on rats using preliminary transection of the spinal cord and injection (in the course of the acute experiment) of 4-aminopyridine. An extremely high (reaching 15–20 mV) amplitude of monosynaptic reflex discharges (MRs) evoked by stimulation of the dorsal root and recorded from the ventral root (VR) L ₄ and the presence of an additional component in the above discharges were phenomena indicative of the development of the above state. Under such conditions, the amplitudes of the discharges evoked in the VR by electrical stimulation of the round window of the labyrinth (vestibular stimulation) and of the discharges elicited by stimulation of the motor cortex under conditions of bilateral transection of the pyramids increased several times. Thresholds of the VR responses to vestibular and cortical stimulations demonstrated an about threefold drop; latencies of the mass responses and responses of single spinal moto-and interneurons decreased about twofold, on average. The pattern of vestibular conditioning effects on the VR MRs changed: in intact animals vestibular stimulation induced inhibition of the VR MRs, while in animals with superreflexia such stimulation led to facilitation of the MRs. Cortical stimulation under conditions of pyramidotomy in both intact animals and animals with superreflexia resulted in facilitation of the VR MRs of a nearly the same intensity. The levels of convergence of the segmental and supraspinal effects on interneurons and motoneurons of the rat spinal cord dramatically increased under superreflexia conditions. The possible mechanisms of augmentation of the descending influences on spinal neuronal systems under the above conditions are discussed. Neirofiziologiya/Neurophysiology, Vol. 38, No. 2, pp. 140–149, March–April, 2006.     

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.     

A comparison of experimental procedures of investigation of the dorsal root evoked ventral root reflex in the frog

Effects of the drug methyl-m-aminobenzoate (MS-222 Sandoz) on the dorsal root evoked ventral root responses were studied by electrophysiological methods in the frog spinal cord. A fairly quick and marked depression of the response was observed from which complete recovery was seen within 60 minutes. Larger doses or repeated injection of small amounts of the drug prolonged the recovery and the monosynaptic discharge component of the ventral root reflex often deteriorated irreversibly. - In further experiments, monosynaptic ventral root discharges were demonstrated in spinal cords isolated from the vertebral canal and kept in Ringer solution. The results are discussed in the light of controversial views about the occurrence of monosynaptic ventral root discharge to stimulation of the primary afferents in the amphibian spinal cord.     

Changes in electrical activity of spinal cord neurons in adrenalectomized rats under the effects of corticosteroid hormones

The effects of glucocorticoid (dexamethasone) and mineralocorticoid (deoxycorticosterone) hormones on electrical excitability of nerve cells belonging to the dorsal and ventral horns of the spinal cord induced by stimulating the sciatic nerve, as well as background and evoked activity in single dorsal horn cells were investigated during experiments on adrenalectomized spinal rats using intracellular techniques for recording potential. Both hormones were found to produce mainly facilitatory effects in adrenalectomized animals, manifesting in increased background activity rates in single cells and higher amplitude of field potentials in nerve cells of the dorsal half of the spinal cord. It was shown that neuronal response followed different patterns in the ventral half of the spinal cord gray matter under the action of gluco- and mineralocorticoids: dexamethasone and deoxycorticosterone respectively increased and reduced the amplitude of field potentials in the motoneuronal region. Findings indicate the modulatory influence of adrenal cortical hormones on the electrical activity of spinal cord neurons.Institute of Experimental Biology, Academy of Sciences of the Armenian SSR, Erevan. I. A. Orbeli Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 21, No. 2, pp. 233–238, March–April, 1989.     

Action of ammonium acetate on central primary afferent depolarization

Experiments on anesthetized spinal cats showed that ammonium acetate, injected intravenously (2–4 mmoles/kg) inhibits the depolarization of the central endings of primary afferent fibers activated by stimulation of afferent nerves. Inhibition of primary afferent depolarization is transient in character and develops parallel with depression of postsynaptic inhibition of monosynaptic reflexes. The depression produced by the action of ammonium was not due to blocking of negative postsynaptic potentials of the dorsal surface of the spinal cord or blocking of reflex electrical discharges in the ventral spinal roots. It is suggested that depression of primary afferent depolarization is due to a decrease in the emf for synaptic ion currents producing depolarization.Allergologic Research Laboratory, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 9, No. 1, pp. 52–60, January–February, 1977.     

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.     

Effects of Long-Lasting Afferent Activation on Segmental Reflex Responses in Albino Rats,and Modifications of These Effects by Thyroxine and 4-Aminopyridine

In albino rats, we studied the effects of long-lasting tetanization of the dorsal roots of the L ₅ (homosynaptic activation) and L ₄ (heterosynaptic activation) segments on reflex discharges in the L ₅ ventral root evoked by single stimulation of the dorsal root of the same segment. Tetanization trains consisted of 5,000 stimuli applied with frequencies of 10, 50, 100, or 300 sec^–1, and their effects were tested during 10 min. There were no long-term post-tetanic potentiation (PTP) of monosynaptic responses when low frequencies of homosynaptic tetanization (10 and 50 sec^–1) were used. In the case of higher frequencies, PTP was rather clear and long-lasting. Under conditions of heterosynaptic activation, there was no PTP. Facilitation of polysynaptic responses developed at all the frequencies of homosynaptic tetanization used; when heterosynaptic tetanization was applied, such facilitation (although weaker) was also observed. In rats treated with agents increasing the excitability of spinal neuronal systems, such as thyroxine and 4-aminopyridine, tetanization of the studied inputs evoked long-term depression (LTD) of both mono- and polysynaptic components of the reflex discharges instead of PTP. Probable mechanisms of postsynaptic changes in the segmental reflex responses are discussed.     

Posttetanic changes in the afferent and efferent activity of monosynaptic reflex in kittens

Both the afferent volleys from the dorsal root and the monosynaptic reflex discharges from the corresponding ventral root were recorded with hook electrodes during stimulation of the nerves innervating the triceps surae muscles. The effects of conditioning high frequency tetanus on the magnitudes of these afferents and reflex volleys were examined in kittens of postnatal age 1-90 days and in adult cats. In young kittens under barbiturate anaesthesia, large-amplitude monosynaptic reflex discharge can be evoked without prior conditioning. The amplitude of this reflex discharge decreased with increasing age of the animal. Application of conditioning tetanic stimuli to the muscle nerves resulted in posttetanic depression followed by posttetanic potentiation of the monosynaptic reflex. The magnitude of posttetanic depression was much higher than that of potentiation in the first postnatal week. As the age increased, the magnitude of depression decreased while the magnitude of potentiation increased. The afferent volley showed a considerable posttetanic potentiation in older kittens and cats. No significant potentiation or depression was observed in the younger animals. Possible mechanisms contributing to posttetanic depression and potentiation are discussed.     

Inhibitory effect of dopamine on the transmission of excitation in isolated rat spinal cord

The effects of dopamine on ventral root potential produced by a single supramaximal dorsal root stimulation of the dorsal root was investigated during experiments on isolated superfused spinal cord segments from 10–16-day old rats. A reciprocal dose-dependent inhibition of the mono- and polysynaptic components of reflex response was also observed. Minimum effective concentration was 1×10^–8 M dopamine. Extent of reflex response increased in step with dopamine concentration, so that the amplitude of the monosynaptic component of ventral root potential was decreased by 20% and 87% of baseline level by the action of 10^–4 and 10^–3 M dopamine respectively on the cord. The amplitude of the polysynaptic component was thereby decreased by an average of 18% and 87%. Findings indicate that dopaminergic brainstem-spinal pathways contribute to the governing of impulse transmission in the segmental reflex arcs. Inhibition of dopaminergic synaptic transmission probably underlies the increase in latency already described in the literature, as well as the increase observed in the threshold of reflex motor response to nociceptive action following either stimulation of the dopaminergic brainstem structures or intravenous administration of dopamine agonists.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 5, pp. 616–621, September–October, 1986.     

Effect of substances potentiating or inhibiting unit activity in the locus coeruleus on some types of spinal inhibition in cats

Microinjections of aspartic acid and chlorpromazine into the region of the locus coeruleus, which strengthen spontaneous unit activity in that structure, in decerebellate cats anesthetized with chloralose, led to depression of the inhibitory influence of flexor reflex afferents on extensor discharges, but did not change the facilitatory action of these afferents on flexor monosynaptic discharges and had no effect on recurrent inhibition of extensor discharges or reduced it. Microinjection of noradrenalin into this region, which depresses spontaneous unit activity in the locus coeruleus, or of procaine, which blocks action potential generation in neurons, led to potentiation of the inhibitory action of flexor reflex afferents on extensor discharges and to strengthening of recurrent inhibition, but did not affect the facilitatory action of these afferents on flexor discharges. The role of tonic descending influences of the locus coeruleus in the control of spinal inhibition evoked by flexor reflex afferents is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 3, pp. 247–256, May–June, 1981.     

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.     

Changes in segmental reflex responses during stimulation of locus coeruleus and potentiation of the action of catecholamines

Repetitive stimulation of the locus coeruleus (up to 150 µA in strength) was accompanied by marked weakening of the inhibitory action of flexor reflex afferents and of the reciprocal inhibitory action on extensor motoneurons. Meanwhile stimulation of this sort had no significant effect on direct inhibition of flexor and extensor motoneurons, on the facilitatory action of flexor reflex afferents and the reciprocal inhibitory action on flexor motoneurons and also on dorsal root potentials. Intravenously injected pyrogallol had a similar action, but its effect was much weaker after spinalization of the animals or blocking of spinal cord conduction by cold. Enhancement of the monosynaptic reflex, which also was observed after injection of pyrogallol, was characterized by different temporal parameters; the intensity of this effect was unaffected both by spinalization and by cold block. These data, and also the results of experiments with partial divisions of the spinal cord, suggest that the effects of stimulation of the locus coeruleus are the result of activity of a descending coerulo-spinal tract, running in the ventral quadrant of the spinal cord.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 1, pp. 39–47, January–February, 1981.