Androgens modulate endplate size and ACh receptor density at synapses in rat levator ani muscle.

The dorsal bulbocavernosus or "levator ani" muscle of the rat is highly responsive to androgens. Both the muscle and the motoneurons which innervate it contain high concentrations of androgen receptors. The neuromuscular synapses in this muscle are also affected by changing androgen levels. In particular, the total number of ACh receptors (AChRs) in the muscle is lower in males that have been castrated, and it increases after treatment with the androgens, testosterone and 5 alpha-dihydrotestosterone. An examination of individual endplates using histochemistry and quantitative autoradiography suggested that the reduction in AChR number following castration is caused by reductions in both the size of endplates and in the density of AChRs at each synapse.