Effect of Chronic Muscle Stretching on Neuromuscular Transmission of Rat Soleus Muscle

An electrophysiological study of neuromuscular transmission and a histochemical study of terminal size were made in tibial nerve-soleus muscle preparations. Preparations were obtained from rats subjected to a leg-lengthening (LL) operation or a leg-lengthening operation with dislocation of the knee joint (LLD operation). The following results were obtained. 1. The time course patterns of change in the mean quantal content, probability of quantal release and the number of releasable quanta in the LLD-operated preparations were similar to those in the LL-operated preparations until the 30th day. However, there were distinct differences between time course patterns in the LLD-operated and the LL-operated preparations after the 40th day. 2. The frequency of complex e.p.p. was significantly higher than the contralateral control in the LLD-operated preparations from the 7th day to the 90th day. On the other hand, the frequency of complex e.p.p. in the LL-operated preparations was similar to that in the LLD-operated preparations until the 30th day. In the LL-operated preparations from the 40th day, however, the frequency of complex e.p.p. was significantly lower than the contralateral control. 3. In both the LL-operated and the LLD-operated preparations, the frequency of nodal sprouting correlated closely with the frequency of complex e.p.p. However, the frequency of nodal sprouting tended to exceed the frequency of complex e.p.p. On the basis of these results, the effect of chronic muscle stretching on neuromuscular transmission is discussed