Colocalization of neuronal nitric oxide synthase and androgen receptor immunoreactivity in the premammillary nucleus in rats

To analyze the importance of premammillary region in male behavior such as aggression and mating, distribution of androgen- and estrogen-receptors (AR and ER), aromatase (ARO) and neuronal nitric oxide synthase (nNOS) was studied in the dorsal and ventral premammillary nuclei (PMd and PMv) of the rat by immunohistochemistry. The nNOS-immunoreactivities (-IR) were present both in the PMd and the PMv, while AR-IR were detected only in the PMv. AR-IR became undetectable after orchidectomy but they recovered by an injection of 5 alpha-dihydrotestosterone (DHT). In both nuclei, no clear signals of ER-IR were encountered. On the other hand, ARO-IR were found in the PMv but only very few. In the PMv, although DHT did not increase nNOS-IR significantly in castrated males, all the nNOS-IR cells contained AR-IR at least in intact and castrated-DHT injected males. Thus, involvement of nNOS-nitric oxide system in the PMv in the androgenic action on male behaviors was suggested.