Projections of afferent ventral root fibers on dorsal horn neurons in the cat spinal cord

Mechanisms of the effect of stimulation of afferent fibers in ventral roots on dorsal horn interneurons were investigated in experiments on anesthetized cats. Dorsal horn interneurons on which such fibers project were shown to exist. In particular, some dorsal horn interneurons can exert an inhibitory influence on effects of dorsal root fiber activation.Institute of Physiology, Academy of Sciences of the Kazakh SSR, Alma-Ata. Translated from Neirofiziologiya, Vol. 17, No. 3, pp. 300–305, May–June, 1985.     

Neurochemical and ionic mechanisms of dorsal root potentials in the spinal cord of immature rats

Dorsal root potentials (DRPs) were recorded by a sucrose gap method in experiments on parasagittal slices of the isolated rat spinal cord. In most cases the DRP consisted of fast and slow waves. The fast wave of DRP was inhibited by the GABA antagonist picrotoxin and the blocker of GABA-activated chloride channels, furosemide, but it was potentiated by pentobarbital sodium. The slow wave of DRP disappeared if the extracellular K⁺ concentration was raised to 10 mM and it was depressed by tetraethylammonium and 4-aminopyridine, blockers of electrically excitable potassium channels. It is concluded that the fast wave of DRP and the initial components of the slow wave of DRP are GABA-ergic in origin; the slow wave of DRP, however, is linked with an increase in extracellular K⁺ concentration near the primary afferent terminals. The possible mechanisms of the increase in extracellular K⁺ concentration during dorsal root stimulation are discussed.A. M. Gor'kii Donetsk Medical Institute. Translated from Neirofiziologiya, Vol. 16, No. 6, pp. 796–800, November–December, 1984.     

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.     

The dorsal root reflex in isolated mammalian spinal cord

1. The dorsal root reflex has been investigated in an isolated preparation of adult mammalian spinal cord. 2. Both evoked and spontaneous activity can be recorded from the cord in the dorsal spinal roots. 3. The spontaneous activity has a characteristic pattern of firing in bursts of action potentials. Spontaneous and evoked activity are optimum at temperatures between 25 and 27 degrees C; little activity can be detected above 35 degrees C. 4. The spontaneous dorsal root activity has been shown to be correlated with negative potentials in the dorsal horn of the cord, and intracellular recordings made from primary afferent fibres have shown spontaneous primary afferent depolarizations (PAD) which underlie the generation of the spontaneous dorsal root activity. 5. The evoked dorsal root reflex has been shown to spread up to 16 spinal segments both rostrally and caudally from the stimulated dorsal root, and to the contralateral side of the cord. 6. The spontaneous dorsal root activity in widely separated segments has been shown by cross-correlation analysis to be linked both ipsi- and contra-laterally. 7. The significance of such a widespread system for the generation of PAD is discussed.     

Effect of bemegride on root potentials of the frog spinal cord

The effect of the convulsant bemegride (β-ethyl-β-methylglutarimide) on spinal-root potentials was investigated in frogs. After intravenous injection in subconvulsant doses (5–12 mg/kg) bemegride caused rapid depression of the dorsal-root potentials evoked by stimulation of the neighboring dorsal or ventral root. Their amplitude fell by 55–67% 3–6 min after bemegride injection. The action of bemegride was reversible and the amplitude of the dorsal-root potentials returned to its initial level within 1 h. Ventral-root potentials showed greater fluctuations of amplitude after injection of bemegride than in the control. Bemegride is evidently an effective agent blocking depolarization of primary afferents in the frog spinal cord.     

Effects of dorsal root section and occlusion of dorsal spinal artery on the neurotransmitter candidates in rat spinal cord

In order to obtain further evidence of putative neurotransmitters in primary sensory neurons and interneurons in the dorsal spinal cord, we have studied the effects of unilateral section of dorsal roots and unilateral occlusion of the dorsal spinal artery on cholinergic enzyme activity and on selected amino acid levels in the spinal cord. One week after sectioning dorsal roots from caudal cervical (C₇) to cranial thoracic (T₂) levels, the specific activity of choline acetyltransferase (ChAT) was significantly decreased and acetylcholinesterase (AChE) showed a tendency to decrease in the dorsal quadrant on the operated side of the spinal cord. Dorsal root sectioning had little effect on the levels of free glutamic acid or other amino acids in the dorsal spinal cord. These results suggest that primary sensory neurons may include some cholinergic axons, and that levels of putative amino acid transmitters are not regulated by materials supplied by axonal transport from the dorsal root ganglia. By contrast, one week following unilateral occlusion of the dorsal spinal artery, the activities of ChAT and AChE were unchanged in the operated quadrant of the spinal cord, while decreases of Asp, Glu, and GABA, and an increase in Tau were detected. These findings are consistent with the proposals that such amino acids, but not ACh, may function as neurotransmitter candidates in interneurons of the dorsal spinal cord.Abbreviation used ACh acetylcholine - AChE acetylcholinesterase - Asp aspartic acid - ChAT choline acetyltransferase - GABA -aminobutyric acid - Glu glutamic acid - Gly glycine - SP substance P - Tau taurine     

Respiratory resetting induced by spinal cord stimulation in the cat

Electrical stimulation (50-150 microA, 0.5-ms duration, 3-300 Hz) was performed within three different regions (lateral, ventrolateral, and ventral) of the C2-C3 spinal cord of decerebrate, vagotomized, paralyzed, and artificially ventilated cats. Spinal cord stimulation sites were located by inserting monopolar or bipolar stimulating electrodes either at the dorsolateral sulcus or at least 1 mm medial or lateral to the sulcus. With stimulation at each site, alterations in respiratory rhythm, orthodromic phrenic nerve responses, and antidromic activation of medullary respiratory-modulated neurons were examined. Phrenic nerve responses to cervical spinal cord stimulation consisted of an early excitation (2-4 ms) and/or a late excitation (4-8 ms). Stimulation of the lateral region evoked the greatest amplitude early response and stimulation of the ventrolateral region produced the greatest late excitation. All three stimulus sites elicited antidromic activation of some respiratory-modulated neurons in the dorsal (DRG) and ventral respiratory groups (VRG). The lateral region was the least effective resetting site, and it had the highest incidence of antidromic activation of both DRG and VRG neurons. The ventrolateral region of the cervical spinal cord was the most effective resetting site, but it had the lowest incidence of antidromic activation of DRG respiratory-modulated neurons. In addition, resetting responses were observed with spinal cord stimulation at similar sites in the thoracic and lumbar spinal cord regions thought to be devoid of inspiratory bulbospinal axons.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of SHF waves on the evoked potentials in the cat spinal cord

In experiments with adult cats there revealed a pronounced effect of SHF radiation on the electrogenesis of spinal cord, the beam density being 15 mW/cm2 and time of exposure 10 min. The estimates of the induced somatosensory brain potentials indicate that there is a phase of a 20 per cent response inhibition with the effect reaching maximum 2-3 h following irradiation. Subsequently, potential characteristics are exponentially restored to be the same with the control values. The evidence is presented that the synaptic neuron contacts within the reflex arc are highly susceptible to SHF radiation.     

Influence of spinal cord stimulation on peripheral blood flow

In 27 vasculopathic and 9 nonvasculopathic patients who underwent spinal cord stimulation to treat pain in lower extremities, Doppler recordings and thermography were used to study peripheral blood flow changes during stimulation. Generally, poststimulation pain relief coincided with a improvement of Doppler recording, a normalization of morphology and increase of pulse wave amplitude, and a rise of skin temperature in the painful area.     

Dorsal root potentials evoked by stimulation of cutaneous afferents in the spinal cat (study of the N3 wave)

The comparative study, when stimulation is increased, of the amplitude changes shown by the negative waves of dorsal root potentials, indicates that the N1 and N2 waves are evoked by A alpha cutaneous afferent, whereas N3 wave is due to A alpha, A beta and perhaps A delta cutaneous afferents. On the other hand, a possible inhibitory action of N1, N2 negative complex on N3 wave is postulated.     

Acute and chronic effects of LSD and 5-MeODMT on raphe-evoked dorsal root potentials in the cat

Both acute and chronic effects of lysergic acid diethylamide (LSD) and 5-methoxy-N, N-dimethyltryptamine (5-MeODMT) on the dorsal root potential (DRP), evoked by stimulation of the nucleus raphe magnus of the cat, were examined. Single injections of LSD potentiated while those of 5-MeODMT inhibited the raphe-evoked DRP. The electrophysiologic response produced by each drug correlates well in dosage and time-course with their reported behavioral effects. Following four consecutive daily injections of LSD, complete tolerance developed to the potentiating effect of LSD on this potential. A similar pretreatment schedule with 5-MeODMT failed to alter its acute inhibitory effect on the DRP. These results correlate well with the development of tolerance to the behavioral effects of LSD and 5-MeODMT. This system may thus provide a unique electrophysiological model to examine the effects of these drugs.     

Excitation of cat spinal cord dorsal column fibers during stimulation of different fiber groups of cutaneous and somatic nerves

The effects of electrically stimulating different groups of nerve fibers supplying the skin and muscle on evoked potentials in cat spinal cord dorsal columns were studied. Significant differences in the configuration of dorsal column potentials recorded in response to stimulation of these nerves were found. It was shown that cutaneous nerve unmyelinated fibres were connected to unmyelinated dorsal column fibers. In addition, excitation of cutaneous C-fibers lead to activation of dorsal column fibers with the maximum conduction velocity. The somatic nerve was only connected to myelinated dorsal column fibers, and excitation of its non-myelinated fibers did not cause other types of dorsal column fibers to be activated. It is suggested that the acceleration of cutaneous signal transmission in the dorsal column system may be brought about by the necessity for rapid warning of potentially harmful stimuli.Medical Institute, Russian Federation Ministry of Public Health, Nizhny Novgorod. Translated from Neirofiziologiya, Vol. 24, No. 5, pp. 625–635, September–October, 1992.