Immunocytochemical analysis of pituitary cells in pre-spawning chum salmon

Pituitary hormones regulate various physiological functions during spawning migration in salmonid. Cytological features of pituitary cells were theref ore immunocytochemically examined by use of antisera against homologous hor mones in pre-spawning chum salmon (Oncorhynchus keta) caught from Ishikari Bay and the Chitose River in October, 1996. Immunoreactivity and sizes of p ituitary cells were determined by a computer-aided image analyzing techniqu e. Immunoreactivity in growth hormone (GH) cells was stronger with enlarged cell sizes in freshwater (FW) fish than in seawater (SW) ones of both sexe s. Majority of prolactin (PRL) cells also had significantly stronger immuno reactivity with enlarged cell sizes in FW fish than in SW animals of both s exes. Immunoreactivity in somatolactin (SL) cells was markedly stronger wit h enlarged cell sizes in FW fish than in SW ones of both males and females. In addition, greater portions of SL cells were strongly stained in FW anim als than in SW ones. A greater portion of gonadotropin (GTH) I cells had st ronger immunoreactivity with reduced cell sizes in FW fish of both sexes, w hen compared with SW fish. Conversely, GTH II cells had significantly stron ger immunoreactivity with enlarged cell sizes in FW ones of both sexes. In proopiomelanocortin (POMC)-derived hormone producing cells, adrenocorticotr opin (ACTH) cells had stronger immunoreactivity in FW animals of both sexes , while cell sizes did not change. In melanotropes, the cells immunoreactiv e to alpha-melanophore stimulating hormone (alpha-MSH) antiserum had strong er immunoreactivity with reduced cell sizes only in FW males, while the cel ls immunoreactive to beta-endorphin antiserum had stronger immunoreactivity with reduced cell sizes in FW fish than in SW animals of both sexes. Impli cation of these results was discussed along with previous reports on gene e xpression of pituitary hormone precursors.