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 suc h as aggression and mating, distribution of androgen- and estrogen-rec eptors (AR and ER), aromatase (ARO) and neuronal nitric oxide synthase (nNOS) was studied in the dorsal and ventral premammillary nuclei (PM d and PMv) of the rat by immunohistochemistry. The nNOS-immunoreactivi ties (-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 (DH T). 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 PM v, although DHT did not increase nNOS-IR significantly in castrated ma les, all the nNOS-IR cells contained AR-IR at least in intact and cast rated-DHT injected males. Thus, involvement of nNOS-nitric oxide syste m in the PMv in the androgenic action on male behaviors was suggested.