Estrogen receptor immunoreactivity in prepubertal and adult male Syrian hamsters.

Estrogen and estrogen receptors (ER) are involved in the expression of steroid-dependent male sexual behavior and negative feedback regulation of the hypothalamic-pituitary-gonadal axis. The purpose of the present experiment was to determine whether there are pubertal changes in ER expression in brain that are correlated with pubertal changes in responsiveness to steroid negative feedback and behavioral activation. We found equivalent numbers of ER-immunoreactive (ER-ir) cells in castrated prepubertal and adult male hamsters in nuclei that comprise the neural circuit that mediate male sexual behavior. Therefore, increases in the number of cells in these nuclei that express ER are not correlated with the increased behavioral responsiveness to steroid hormone shown by hamsters after puberty. The number of ER-ir cells in the ventral medial hypothalamus was less in adults compared with juveniles. This pubertal decrease in ER expression is correlated with the decreased responsiveness to steroid negative feedback in the adult.