IMMUNOHISTOCHEMICAL LOCALIZATION OF GLUCOCORTICOID RECEPTORS IN THE FOREBRAIN OF THE RAINBOW-TROUT (ONCORHYNCHUS-MYKISS)

The distribution of glucocorticoid receptor-expressing cells was studi ed in the forebrain of the rainbow trout by means of antibodies produc ed against a fusion protein made of the NH2-terminal fragment of the r ainbow trout glucocorticoid receptor fused in frame with glutathione-S -transferase. The results indicate that glucocorticoid receptor-expres sing cells are located in many brain regions from the telencephalon to the spinal cord, with the highest density in the neuroendocrine compo nent of the brain, the preoptic region and the mediobasal hypothalamus , and in the periventricular zone of the optic tectum. In virtually al l cases, the labeling was located in the nucleus of the cells, althoug h on very rare occasions, a slight labeling of the cytoplasm was detec ted. Concerning the preoptic region, the most striking feature was the high density of glucocorticoid receptors in the magnocellular preopti c nucleus, known to contain corticotrophin-releasing factor (CRF)-, va sotocin-, and isotocin-expressing cells. Colocalization experiments sh owed that 100% of the CRF-immunoreactive neurons in the preoptic nucle us express glucocorticoid receptors. In the mediobasal hypothalamus, t he highest expression was found in the nucleus lateralis tuberis and p arts of the nucleus recessus lateralis. Concerning the pituitary, the glucocorticoid receptor was consistently found in the rostral pars dis talis, with the exception of the prolactin cells, and in the proximal pars distalis, which in trout contains thyrotrophs, gonadotrophs, and somatotrophs. In the hindbrain, expression of glucocorticoid receptors were localized mainly in the periventricular regions. J. Comp. Neurol . 401:395-410, 1998. (C) 1998 Wiley-Liss, Inc.