Androgen receptor immunoreactivity of male rat cervical motor neurons is increased by chronic pharmacologic testosterone treatment.

Chronic pharmacologic testosterone treatment of adult male rats decreases neuromuscular transmission failure (NTF) in the rat diaphragm muscle and increases choline acetyltransferase (ChAT) mRNA levels in cervical motor neurons. These testosterone-induced changes in NTF and ChAT mRNA levels may be mediated through the activation of the androgen receptor (AR). The purpose of this study was to determine if the AR expression of cervical motor neurons is modulated by chronic pharmacologic testosterone treatment of gonadally intact male rats with testosterone propionate (TP). Serum testosterone levels were elevated by a subcutaneous implant of capsules containing crystalline TP for 28 days. The proportion of motor neurons containing AR-I positive nuclei was increased from 14.8 +/- 10.8% among the control group to 81.7 +/- 12.6% in the TP-treated animals (p<0.05). These results imply that anabolic-androgenic steroid effects on neuromuscular function may be mediated through AR dependent regulation of gene expression in motor neurons.