DISTRIBUTION OF ESTROGEN RECEPTOR-IMMUNOREACTIVE CELLS IN THE BRAIN OF THE RAINBOW-TROUT (ONCORHYNCHUS-MYKISS)

Using antibodies against the hormone binding domain of the trout estro gen receptor (ER), the distribution of ER-immunoreactive (ER-IR) cells was studied in the brain of maturing diploid and triploid female rain bow trout using a streptavidin-biotin-peroxidase method followed by a nickel-intensified diaminobenzidine reaction. This technique resulted in an excellent signal/background ratio allowing unambiguous identific ation of positive cells. In all animals, ER-IR cells were consistently located in three brain regions, the ventral telencephalon, the anteri or ventral preoptic region, and the mediobasal hypothalamus. About 250 ER-IR cells were observed in the ventral and dorsal parts of the vent ral telencephalon. In the anterior nucleus preopticus periventriculari s, about 2400 ER-IR cells were observed surrounding the preoptic reces s. In the posterior hypothalamus, approximately 2700 ER-IR cells were located in the anterior, posterior and inferior divisions of the nucle us lateralis tuberis and in the nucleus saccus vasculosus. In these re gions, cell nuclei exhibiting different densities of staining were obs erved and absolutely no labeling of cytoplasmic processes was detected . These results are in partial agreement with those obtained either af ter injection of tritiated-estradiol in other teleots species or in si tu hybridization of ER mRNAs in trout. In particular, no immunoreactiv ity was observed in the thalamic region nor in the nucleus posterioris periventricularis. These data indicate that target cells for estradio l are essentially located in brain regions involved in the neuroendocr ine control of pituitary functions and having direct connections with the hypophysis.