Testosterone increases acetylcholine receptor number in the "levator ani" muscle of the rat.

The "levator ani" muscle of male rats provides a neuromuscular system in which both the muscle and its motoneurons have high levels of androgen receptors. Two weeks of castration caused a 48% loss of acetylcholine receptors in this muscle. One week of testosterone propionate injections initiated on week after castration increased receptor number by 27% over untreated castrate levels. These changes paralleled changes in muscle protein content. In contrast, castration and testosterone treatments of castrates had no effect on total. Triton X-100-extractable acetylcholinesterase activity. This system may provide a useful model of synaptic plasticity.