Nimodipine suppresses preferential reinnervation of mouse soleus muscles by slow alpha-motoneurons

Denervation of mouse soleus muscle followed by self-reinnervation causes a significant increase in slow twitch (type I) muscle fiber content, suggesting preferential reinnervation by slow alpha-motoneurons. Since intracellular Ca2+ influences both axonal elongation rate and branching, we examined the process of self-reinnervation in mouse soleus muscles in the presence of the L-type Ca2+ channel blocker nimodipine. Soleus muscles in both control and experimental animals were denervated by crushing the soleus nerve where it enters the muscle. Experimental animals received a daily i.p. injection of a 0.1% nimodipine solution beginning 4 days prior to denervation and ending 2 weeks postdenervation. At 2 months postdenervation reinnervated and contralateral muscles from both control and experimental animals were sectioned and histochemically stained for myosin ATPase to determine the percentage of slow twitch fibers in the muscles. It was found that, in agreement with previous experiments, untreated reinnervated muscles had a significantly higher percentage of slow twitch fibers than did their contralateral controls (91.3 versus 74. 6%). However, in nimodipine-treated animals only a small, but not statistically significant, difference between reinnervated and contralateral control muscles was observed (76.5 versus 72.8%). These results suggest that Ca2+ influx through L-type calcium channels in growing neurites may play a role in the outcome of the reinnervation process.