DO GONADOTROPIN-RELEASING-HORMONE NEURONS EXPRESS ESTROGEN-RECEPTORS IN THE RAINBOW-TROUT - A DOUBLE IMMUNOHISTOCHEMICAL STUDY

A double immunocytochemical procedure, with two different chromogens, was used to compare the respective distributions of estrogen receptor- immunoreactive cells and gonadotrophin-releasing hormone-immunoreactiv e neurons on the same sections of the brains of adult male and female rainbow trout (Oncorhynchus mykiss). Estrogen receptor-immunoreactive cells were observed in the ventral and lateral telencephalon, the preo ptic region, the mediobasal hypothalamus, and the ventromedial thalami c nucleus. Gonadotrophin-releasing hormone-immunoreactive perikarya we re detected in the olfactory bulbs, the ventral telencephalon, the pre optic area, and the mediobasal hypothalamus. Double-staining studies s howed that, although some estrogen receptor-positive cells were in clo se proximity to gonadotrophin-releasing hormone-immunoreactive perikar ya, careful examination of 550 gonadotrophin-releasing hormone-positiv e cells from five adult females and two adult males failed to demonstr ate any evidence that gonadotrophin-releasing hormone neurons coexpres s estrogen receptor in the brain of the rainbow trout. The present stu dy provides, for the first time in teleosts, morphological evidence th at gonadotrophin-releasing hormone neurons do not represent major dire ct targets for estradiol, suggesting that the positive feedback effect s of estradiol onto the gonadotrophin-releasing hormone system are lik ely to be conveyed via other cell populations. (C) 1995 Wiley-Liss, In c.