Denervation of mouse soleus muscle followed by self-reinnervation causes a
significant increase in slow twitch (type I) muscle fiber content, suggesti
ng preferential reinnervation by slow alpha-motoneurons. Since intracellula
r Ca2+ influences both axonal elongation rate and branching, we examined th
e 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 en
ding 2 weeks postdenervation. At 2 months postdenervation reinnervated and
contralateral muscles from both control and experimental animals were secti
oned and histochemically stained for myosin ATPase to determine the percent
age of slow twitch fibers in the muscles. It was found that, in agreement w
ith previous experiments, untreated reinnervated muscles had a significantl
y higher percentage of slow twitch fibers than did their contralateral cont
rols (91.3 versus 74.6%). However, in nimodipine-treated animals only a sma
ll, but not statistically significant, difference between reinnervated and
contralateral control muscles was observed (76.5 versus 72.8%). These resul
ts suggest that Ca2+ influx through L-type calcium channels in growing neur
ites may play a role in the outcome of the reinnervation process. (C) 1998
Academic Press.