Abstract

The effects of varying strengths of stimulation, physostigmine, dihydro-beta-erythroidine and mephenesin on the frequency of spike activity of the Renshaw cell have been investigated. In agreement with Renshaw (1946) and Eccles (1954), it was found that increasing strength of stimulation produced an increase in frequency and duration of discharge of the Renshaw cell, and that physostigmine prolonged the duration of the Renshaw burst. However, measurements of the relationship between the time course of the Renshaw burst and stimulus strength yielded data inconsistent with the hypothesis that the duration of the burst is determined solely by the rate of hydrolysis of acetylchohine. The effect of physostigmine in prolonging the Renshaw burst can be explained on the basis that, in the presence of a reduced concentration of effective esterase, the rate of hydrolysis of ACh would proceed at a slower rate and the concentration of ACh available for combination with effector receptors would be increased.

Dihydro-beta-erythroidine, as Eccles et al. (1954, 1956a) have previously reported, attenuated the duration of the Renshaw burst. In addition, it decreased the frequency of the burst during the first 5 milliseconds. Mephenesin produced a modest depression of the Renshaw burst that was probably of the same order of magnitude as that observed with pentobarbital by Eccles et al. (1956a).