Further observation of reflex potentials in the lumbar sympathetic trunk in cats.

Abstract

Response patterns of the reflex potentials in the lumbar sympathetic trunk were analyzed repeatedly in 25 chloralose anesthetized cats, double shock stimulations as well as repetitive ones being delivered to either the sciatic or the radial nerve.1. With a single shock stimulation of either nerve, two kinds of reflex potentials, the early reflex potential (ERP) of spinal origin and the late one (LRP) of supraspinal origin, were obtained in all the 21 animals of intact spinal cords examined. The ERP was observed more frequently by the sciatic nerve stimulation (76.2%) than by the radial nerve one (23.8%), although the LRP was obtained in all the 21 animals irrespective of the nerves under stimulation. Throughout this series of experiments, no appreciable difference was recognized between the sides of the nerves under stimulation.2. As a result from double shock stimulations of either the sciatic or the radial nerve, the LRP showed significantly ealier recovery curves than the ERP in 5 animals of intact spinal cords examined, namely they appeared respectively at intervals of approximately 600 msec and 1.3 seconds and recovered completely at intervals of 2.2 and 2.5 seconds. It was noted that recovery curves of the ERP shifted markedly to the left side of those of the LRP and ERP noted above following spinal cord transection at the C1 level, showing their minimum reflex responses at intervals of as short as approximately 150 msec and their complete recovery at those of about 1.4 seconds. No appreciable difference was observed between the nerves under stimulation including their sides. Mechanisms of these phenomena were discussed.3. Repetitive stimulations of varied frequencies for 15 seconds were delivered to the sciatic nerve in 8 animals with intact spinal cords. Reduction of amplitudes of reflex responses except for dominant, initial responses were observed which recovered gradually at frequencies below 4/sec during the stimulation, although no reduction was recognized at frequency below 0.3/sec. With increase in frequency above 5/sec, reflex responses fused together to DC potential shifts of maximum 70μV with irregular waves on them during the stimulation, showing maximum values at frequencies from 10 to 50/sec.Dominant, initial responses were observed throughout this series of experiments. It was also noted that depressions of spontaneous potentials lasted for 7 seconds after cessation of the stimulation, showing longer durations with increase in frequencies.4. Response patterns of reflex potentials which were observed in 4 spinal animals likewise with repetitive stimulations of the sciatic nerve, were quite different from those in animals of intact spinal cords noted above, as was expected from the distinctly early recovery curve of the ERP in these spinal animals.5. Results of unitary reflex discharges obtained in 6 animals of intact spinal cords with repetitive stimulations of varied frequencies of the sciatic nerve were compatible with those of reflex responses with repetitive stimulations noted above, showing marked, initial bursts of discharges following by pauses of discharges for 1-2 seconds and maximum discharges during the stimulation above 10 to 50/sec frequencies of stimulations.