PHYSIOLOGIC CHARACTERISTICS OF REGENERATING MAMMALIAN NERVE AND MUSCLE

Abstract

In rat gastrocnemii early in the course of regeneration of their crushed tibial nerves (21 days after operation), duration of single muscle twitches, particularly the relaxation phase, elicited by nerve stimulation, was significantly prolonged. Later in regeneration (35 days) twitch duration again approached normal values. This prolonged twitch was not due to the presence of a large mass of denervated muscle tissue. The interval between onset of initial shortening and max. shortening, developed on indirect repetitive stimulation, was significantly less in regenerating than in normal muscle. Since this was also found in partially denervated muscle (L5 section), it is not an exclusive characteristic of early regeneration, but may be due to fewer active muscle fibers being reached by nerve impulses, hence an earlier attainment of summated max. tension. There was a greater degree of fusion of individual twitches at low stimulus frequencies (15 and 30 per sec.) in regenerating than in normal muscles. The extent of wave summation, on indirect stimulation, was less in regenerating than in normal control muscle. Also a lower stimulus frequency was required to produce max. summation in regenerating than in normal muscle. A muscle early in regeneration exhibited a more rapid transmission fatigue, on repetitive indirect stimula tion, than did a normal muscle. This phenomenon may be due to a deficiency of cholinesterase, although a persisten increased sensitivity to endogenous acetylcholine may also play a part.