ANDROGEN RECEPTOR-LIKE IMMUNOREACTIVITY IN THE BRAZILIAN OPOSSUM BRAIN AND PITUITARY - DISTRIBUTION AND EFFECTS OF CASTRATION AND TESTOSTERONE REPLACEMENT IN THE ADULT MALE

Androgens are involved in a variety of centrally mediated functions af ter binding to their intracellular receptors. In the present report, w e have employed the androgen receptor antibody, PG-21, and indirect im munohistochemistry to examine the distribution of cells containing and rogen receptor-like immunoreactivity (AR-IR) in the intact adult male Brazilian opossum brain and pituitary. Additional adult males were cas trated to examine the effects of withdrawal of circulating androgens a nd testosterone replacement on AR-IR. Immunoblots and immunohistochemi cal controls demonstrated that the androgen receptor in the opossum br ain and peripheral tissues are of a similar molecular mass as to has b een reported for the rat. Cells containing AR-IR were widely distribut ed throughout the brain of intact adult males. The highest number of i mmunoreactive cells were present in the dorsal and ventral nuclei of t he lateral septum, medial division of the bed nucleus of the stria ter minalis, medial preoptic area, median preoptic nucleus, nucleus of the lateral olfactory tubercle, central amygdaloid nucleus, anterior cort ical amygdaloid nucleus, posterior amygdaloid nucleus, subiculum, vent romedial hypothalamic nucleus, arcuate-median eminence region, and ven tral premammillary nucleus. The anterior pituitary gland also containe d a high number of cells containing AR-IR. The general distribution of AR-IR both in the brain and anterior pituitary gland resembled that r eported for other mammalian species. Castration of the adult males fou r days prior to perfusion eliminated androgen receptor immunostaining throughout the brain except for a few lightly immunostained cells in t he ventral nucleus of the lateral septum and stria terminalis. Androge n receptor immunostaining was decreased in the anterior pituitary glan d following castration and became cytoplasmic. Testosterone administra tion 2 h before perfusion restored AR-IR both in the brain and anterio r pituitary gland. These data suggested that immunohistochemical detec tion of bound (nuclear) androgen receptors as seen with PG-21 antibody in the brain and anterior pituitary gland of the opossum is dependent upon circulating androgens. Further, the wide distribution and simila rity in localization of androgen receptors in the opossum brain and an terior pituitary gland to that of other species suggests that androgen receptors might be involved in similar functions in the opossum as ha s been reported for other species.