Journal of Neuroscience, Vol 9, 229-238, Copyright © 1989 by Society for Neuroscience
The role of gonadal hormones in neuromuscular synapse elimination in rats. I. Androgen delays the loss of multiple innervation in the levator ani muscle
CL Jordan, MS Letinsky and AP Arnold
Department of Psychology, University of California, Los Angeles 90024.
The normal period of synapse elimination in the androgen-sensitive levator
ani (LA) muscle occurs between 2 and 4 weeks after birth, well after the
period of synapse elimination for most other rat muscles. To evaluate
whether gonadal androgen might be involved in the delayed development of
single innervation in the LA, we compared the time course of synapse
elimination in LA muscles that lacked endogenous gonadal androgen or were
exposed to exogenous androgen. Tetranitroblue tetrazolium was used to stain
neuromuscular connections. Our results suggest that both endogenous and
exogenous androgen delay the normal process of synapse elimination.
Removing endogenous androgen resulted in lower levels of multiple
innervation in the LA, suggesting that androgen may normally influence
synapse elimination. Moreover, androgen treatment prevented much of the
normal loss of multiple innervation in the LA. Androgen treatment during
the normal period of synapse elimination also increased the diameter of LA
muscle fibers, enhanced the development of preterminal branching, and
increased the number of junctional sites on some LA fibers. Because
androgen did not appear to induce the formation of new synapses through
sprouting, we conclude that androgen maintained multiple innervation in the
LA by preventing the normal ontogenetic process of synapse elimination.