The role of gonadal hormones in neuromuscular synapse elimination in rats. II. Multiple innervation persists in the adult levator ani muscle after juvenile androgen treatment.

In the previous study (Jordan et al., 1989), we demonstrated that androgen treatment of juvenile male rats inhibits the elimination of synapses in the levator ani (LA) muscle. In the present study, we asked whether synapse elimination would occur once this juvenile androgen treatment ended. Castrated male rats were given androgen during a juvenile treatment period (7-34 d) and were killed 4 or 8 weeks after the end of androgen treatment (at 9 or 13 weeks after birth). The adult pattern of innervation in the LA was assessed (1) anatomically by counting the number of stained motor axons innervating single muscle fibers and (2) electrophysiologically by counting the number of components in intracellularly recorded endplate potentials. Based on the number of stained motor axons, the LA from juvenile androgen-treated castrates had as much multiple innervation 1 and 2 months after the end of androgen treatment (at 9 and 13 weeks) as was present during androgen treatment at 4 weeks. This suggests that no further synapse loss occurred in the LA once androgen treatment ended. Based on electrophysiological measures, adult LA muscles previously exposed to androgen were found to contain significantly more polyneuronal innervation than normal adult LA muscles. Juvenile androgen treatment also increased the size but not the number of motoneurons in the spinal nucleus of the bulbocavernosus which contains LA motoneurons. Thus, the increased level of multiple innervation in the LA is not due to a higher than normal number of motoneurons innervating this muscle. Because multiple innervation persists in the LA in the absence of continued androgen treatment, androgen may have permanently prevented synapse elimination.(ABSTRACT TRUNCATED AT 250 WORDS)