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.     

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.     

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 partial bulbar section on inhibition of jaw-opening reflexes induced by central gray matter stimulation in the cat

The effects of severing the spinal trigeminal tract and its caudal nucleus on high-threshold jaw-opening reflex elicited by tooth pulp stimulation were investigated during experiments on cats under chloralose-Nembutal anesthesia. Low-threshold jaw-opening reflex produced by stimulating the A--infraorbital nerve at an intensity 2–3 thresholds in relation to the most excitable fibers on this nerve was also observed, as well as suppression of these reflexes induced by central gray matter stimulation. It was found that spinal trigeminal tract section produces a 8–52% increase in high-threshold reflex. The amplitude of low-threshold reflex either remained unchanged or showed a slight tendency to rise or fall. Brief stimulation of the central gray matter produced a 100% decrease in high-threshold reflex in intact animals compared with a 40–60% decrease after section of the trigeminal tract. Protracted stimulation of the central gray brought about an 80% decline in high-threshold reflex in intact animals as against 25–30% after section. The degree to which brief stimulation of the central gray produced depression of low-threshold stimulation remained unchanged by trigeminal tract section. Protracted stimulation of the central gray matter brought about a 25–50% reduction in low-threshold reflex in intact animals and a reduction of 75% in three animals and 15–20% in four animals. This implied that the caudal nucleus of the spinal trigeminal tract exerts a more substantial influence on the process of high- than low-threshold reflex inhibition when the central gray matter is stimulated.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 3, pp. 362–368, May–June, 1987.     

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.     

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.     

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.     

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.     

Effect of nociceptive stimulation of signal transmission from low-threshold cutaneous afferents in the somatosensory system

In cats anesthetized with chloralose nociceptive heating of the skin of the foot to 44–60°C led to a two- to fourfold increase in amplitude of primary cortical responses to direct stimulation of neurons of the spinocervical tract receiving information from the heated area of skin, but did not affect primary responses evoked by stimulation of axons of these neurons in the dorsolateral funiculus, and actually inhibited the response to stimulation of the nerve innervating the heated area of skin. Inhibition was accompanied by depolarization of central terminal of low-threshold fibers of this nerve: During heating the amplitude of the antidromic discharges evoked in the nerve by stimulation of its presynaptic endings in the spinal cord was increased two- to threefold. After abolition of presynaptic depolarization with picrotoxin (0.2–0.7 mg/kg, intravenously) or as a result of asphyxia, nociceptive heating acquired the ability to facilitate primary responses arising as a result of stimulation of the nerve also. The amplitude of the responses was increased under these circumstances by 3–20 times. It is concluded that acute nociceptive stimulation causes such powerful presynaptic inhibition of impulse transmission from low-threshold fibers of the cutaneous nerve that it virtually abolishes the facilitating effect of nociceptive impulses on sensory neurons of the spinal cord. It is suggested that it is this inhibitory mechanism which prevents the development of hyperalgesia during acute nociceptive stimulation.Institute of General Pathology and Pathological Physiology, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 13, No. 6, pp. 621–627, November–December, 1981.     

Late long-lasting discharges in hind limb motor nerves and their connection with the locomotor rhythm in thalamic immobilized cats

Effects of stimulation of flexor reflex afferents were studied in decerebrate immobilized cats. Stimulation of ipsilateral afferents evoked late long-lasting discharges in the nerves to the flexors, whereas stimulation of contralateral afferents led to similar discharges in nerves to both extensors and flexors. Compared with spinal animals, early segmental reflexes in thalamic cats were tonically depressed. Similar tonic inhibition of segmental reflexes took place in spinal animals after injection of dopa. Segmental reflexes were clearly modulated during late or rhythmic discharges. The possible central mechanisms of these changes in the segmental reflexes are discussed on the basis of data in the literature.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 11, No. 2, pp. 137–145, March–April, 1979.     

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.     

Recurrent inhibition of sympathetic preganglionic neurons of the lateral horns of the spinal cord

Experiments on anesthetized and immobilized cats showed that repeated antidromic discharges can be evoked in 32.5% of sympathetic preganglionic neurons of the lateral horns in segments T3, T8–9, and L2 of the spinal cord, with intervals of 16 msec or more between them, which is much greater than the refractory period of these neurons. This feature was shown not to be connected with the properties of axons of that group of neurons and, in particular, with their after-subnormality. After orthodromic discharges in neurons of this group, for a much longer period of time than could be accounted for by possible collision, no antidromic discharges likewise were evoked. As a result of antidromic activation of some of these neurons in one segment, definite inhibition of the orthodromic response of other neurons of the same segment appeared, etiher by a reflex mechanism or through stimulation of descending pathways. The results point definitely to the existence of a mechanism of recurrent inhibition in some sympathetic preganglionic neurons of the lateral horns.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 9, No. 4, pp. 382–389, July–August, 1977.     

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.     

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.     

Distribution of myelinated and nonmyelinated nerve fibers of a cat cutaneous nerve in the spinal roots

The distribution of myelinated and nonmyelinated nerve fibers of the saphenous nerve of cats in the ventral and dorsal roots of the spinal cord was investigated by methods improving the signal—noise ratio in records of evoked responses from the nerve. The fibers of this nerve enter the spinal cord through roots of segments L_4–6. Nerve fibers with conduction velocities of between 80 and 0.38 m/sec were distributed in the dorsal roots of these segments. Four groups of nerve fibers with conduction velocities of 80–60, 40–30, 12.0–3.0, and 1.1–0.51 m/sec, possibly afferent in nature, were found in the ventral roots. The conditions of origin and detection of low-amplitude potentials in the roots of the spinal cord and the probable functional role of the nerve fibers in the ventral roots are discussed.Research Institute of Applied Mathematics and Cybernetics, N. I. Lobachevskii State University, Gor'kii. Translated from Neirofiziologiya, Vol. 7, No. 6, pp. 647–654, November–December, 1975.     

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.     

Scratch reflex evoked by strychnine applied to the spinal cord

Effective facilitation of the scratch reflex was observed in experiments on recently decerebrated and spinal cats in response to application of strychnine solution to the dorsal surface of the spinal cord. The receptive fields of the scratch reflex in this case depended on the segments to which the strychnine was applied. The receptive fields of a scratch reflex evoked by D-tubocurarine coincided with those of the intact adult animals, but the receptive fields for strychnine application were wider and corresponded to those of the scratch reflex in kittens [1, 10]. It is suggested that strychnine application abolishes the inhibition of the afferent inputs of the scratch reflex in the lower cervical segments of the spinal cord which has developed during ontogeny.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 6, pp. 622–625, November–December, 1978.     

Functional characteristics and topography of spinal pathways conducting high- and low-threshold startle reflexes

Electrophysiological and topographical properties of the spinal tract systems involved in two functional types of startle reflexes were studied in chloralose anesthetized cats: a high-threshold reflex produced by intense peripheral nerve stimulation (spinobulbo-spinal, SBS, reflex) and a low-threshold reflex evoked by tactile (T-reflex) and acoustic (A-reflex) stimulation. Maximum conduction velocity of descending transmission of the high-threshold reflex, at 30 m/sec, was perceptibly lower than that of low-threshold reflexes, at 85 m/sec for T-reflex and 100 m/sec for A-reflex. Mean conduction velocity for SBS and T-reflexes were 40.2 and 70.8 m/sec respectively. Perceptible differences were also found in the topography of spinal and especially ascending pathways of these reflexes. It was established by partial spinal cord destruction that accomplishment of T-reflex depended on the integrity of ascending pathways of the dorsal and dorsolateral funiculi and the SBS reflex on preservation of the dorsolateral, ventrolateral and (partially) of ventral funiculi. Descending pathways of the reflexes under study were revealed mainly in the ventrolateral and ventral funiculi and those of the SBS reflex mainly in the first of these. Findings also show the noticeable similarity between the organization of both T- and A-reflex descending pathways. The functional organization of the spinal pathways of a variety of startle reflexes is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 4, pp. 486–496, July–August, 1986.     

Depolarizing effects of dopamine on motoneurons from a segment of spinal cord isolated from newborn rats

The effects on dorsal root potentials of applying dopamine to the perfusing fluid were investigated in experiments on a segment isolated from the spinal cord of 13- to 18-day-old rats. Dopamine induced slow, dose-dependent depolarization in motoneurons in 28 trials out of 32, retained in the solution blocking synaptic transmission. Threshold concentration of dopamine in the normal perfusing fluid measured 1·10^–6 M and 1·10^–5 M in a calcium-free perfusate containing magnesium or manganese ions. Depolarization was accompanied by an increased rate of motor discharges recorded from the ventral root. Segmental reflex response produced by dorsal root stimulation was depressed following depolarization. Hyperpolarization in response to dopamine was observed in 4 out of 32 experiments. Dopamine-induced electrotonic dorsal root potentials were suppressed by prior haloperidol application to the brain.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 6, pp. 735–741, November–December, 1987.     

Comparative study of sympathetic and parasympathetic firing in automatic nerves produced by stimulating different structures of the cat hypothalamus

It was discovered by making simultaneous recordings of evoked hypothalamic-parasympathetic and hypothalamic-sympathetic firing that sympathetic discharges in the splanchnic nerve and parasympathetic discharges in the pelvic nerve with minimum latency and lowest threshold level could be obtained by stimulating the posterolateral hypothalamus. It was also found that the focus of maximum neuronal activity produced by stimulating afferent visceral nerve fibers as well as the highest concentration of evoked efferent response in sympathetic and parasympathetic nerves were located in the same hypothalamic area. A working hypothesis was put forward that convergent polysensory hypothalamic neurons also act as divergent polyeffector constituents of the integrative system of the hypothalamovisceral reflex arc.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 19, No. 4, pp. 482–491, July–August, 1987.