PHOTOPERIOD AND STEROID-DEPENDENT ADJUSTMENTS IN HYPOTHALAMIC GONADOTROPIC HORMONE-RELEASING HORMONE, DOPAMINE, AND NOREPINEPHRINE CONTENT IN MALE DEER MICE

The purpose of this study was twofold: 1) to examine photoperiod-depen dent and steroid-dependent adjustments in hypothalamic GnRH and catech olamine content in male deer mice, Peromyscus maniculatus, and 2) to e valuate whether the commonly used measure of GnRH accumulation serves as an accurate indicator of altered reproductive function in short-day -housed rodents, Deer mice provide a unique animal model in which to e valuate the effect of short day length on the neural substrates direct ing reproductive function, since individual deer mice respond to short photoperiod with a range of neuroendocrine, endocrine, metabolic, and thermoregulatory adjustments. These adjustments, in part, result in t wo distinct reproductive phenotypes; reproductively competent ''nonres ponsive'' mice, and gonad-regressed ''responsive'' mice. Reproductivel y mature males were maintained on either long (16L:8D) or short (8L:16 D) photoperiod for 8 wk. Thereafter, mice were phenotyped and either r emained intact, castrated, or castrated and provided with an s.c. test osterone-filled silicons elastomer capsule releasing long-day or twice long-day levels of testosterone; mice were then housed for an additio nal 4 wk. At autopsy, plasma levels of LH and testosterone, hypothalam ic GnRH content, and hypothalamic dopamine and norepinephrine concentr ations were determined. Short photoperiod caused a similar increase in GnRH content in both short-day phenotypes, and this increase was prim arily localized to the medial basal hypothalamus (MBH). Castration dec reased GnRH content within the MBH of mice housed on both a long and s hort photoperiod. However, castration also reduced GnRH content within the medial preoptic area (MPOA) only among the short-day phenotypes. Steroid replacement at levels similar to those of intact long-day male s restored GnRH content in all brain regions to levels of intact mice. On the other hand, steroid replacement at twice long-day levels resto red GnRH content among long-day mice but reduced GnRH content among bo th short-day reproductive response groups, specifically within the MBH and MPOA. There were no dramatic effects of photoperiod or steroid tr eatment on catecholamine concentrations. But our results do suggest th at the lateral preoptic area (LPOA) and MBH may be important sites of steroid feedback among mice exposed to short photoperiods and that the LPOA and diagonal band of Broca-septal regions may specifically be as sociated with catecholamine-directed photoperiod-induced adjustments o f reproductive responsive mice. Taken together, these data show that G nRH accumulation is not the proximate signal directing seasonal change s in pituitary-gonadal function and cast doubt on the use of this fact or as an accurate indicator of altered reproductive function.