Androgenic regulation of expression of androgen receptor protein in the perineal motoneurons of aged male rats.

Androgen might regulate expression of androgen receptors (AR) in AR-containing motoneurons in young animals. In the present study, it was examined whether expression of AR was also regulated by androgen in aged animals. Twelve male rats were castrated at 26 months of age. Five days following castration, the animals were treated with testosterone propionate (TP; six males) or vehicle (six males) and killed 2 hours later. Six sham-castrated rats served as controls. AR immunoreactivity was examined in motoneurons of the spinal nucleus of the bulbocavernosus (SNB) in these animals by immunohistochemistry using the polyclonal antibody PG21. In control animals, slightly intense AR immunoreactivity was confined to the nuclei of the motoneurons. AR immunoreactivity was completely eliminated in the motoneurons of castrated rats. In castrated, aged animals treated with TP, the intensity of AR immunoreactivity in the nuclei of SNB motoneurons was increased. Plasma levels of testosterone in castrated, aged animals 2 hours following treatment with TP were significantly greater than those in controls. These results suggest that expression of AR in motoneurons of the SNB in aged male rats is up-regulated in response to androgen and that androgen may be, at least in part, involved in the process of aging of the SNB in male rats.