ANDROGEN REGULATION OF HYPOTHALAMIC NEURONS CONTAINING GONADOTROPIN-RELEASING-HORMONE IN A CICHLID FISH - INTEGRATION WITH SOCIAL CUES

Reproduction in vertebrates is regulated by internal signals such as h ormone levels and by external signals such as social interactions. In an African cichlid fish, Haplochromis burtoni, the effect of social in teractions is evident in the hypothalamo-pituitary-gonadal (HPG) axis of males. Territorial males, characterized by aggressive and reproduct ive activity, have significantly larger hypothalamic gonadotropin-rele asing hormone (GnRH)-containing neurons and larger testes than nonterr itorial males. Furthermore, a switch in the social status of an adult male causes a corresponding change in GnRH neuron size and testis size . Here we show that the GnRH-containing neurons in the hypothalamus of adult territorial males are also influenced by gonadal hormones. Cast ration of territorial males caused GnRH neurons to increase in size. T his neuronal hypertrophy in castrated animals was prevented either by testosterone (T) or 11-ketotestosterone (KT) treatment. Estradiol (E2) treatment did not reduce GnRH cell size in castrated animals. These r esults suggest that androgens reduce the size of GnRH cells through ne gative feedback. Since E2 had no effect, androgen influence on GnRH ce ll size appears to be independent of aromatization. These data are con sistent with the hypothesis that the setpoint for hypothalamic GnRH ce ll size is determined by social cues and that this setpoint is maintai ned by negative feedback from gonadal androgens. (C) 1996 Academic Pre ss, Inc.