Cell density and intracellular translocation of glucocorticoid receptor-immunoreactive neurons in the kokanee salmon (Oncorhynchus nerka kennerlyi) brain, with an emphasis on the olfactory system

This study tested the hypothesis that neurons in olfactory regions of the k okanee salmon brain contain glucocorticoid receptors. Distribution and neur onal number of glucocorticoid receptor-like immunoreactive (GRir) neurons w ere identified in the kokanee salmon brain using immunohistochemistry with an antibody to GR (polyclonal rabbit anti-human, dilution 1:1500; and monoc lonal mouse, dilution 5 mu g/ml). Distribution of GRir neurons similar to t he mammalian pattern was observed in the brains of sexually immature (n = 8 ; 4 female and 4 male) as well as spawning(n = 8; 4 female and 4 male) salm on. Olfactory-related areas containing GRir positive neuronal bodies includ ed the internal cell layer of the olfactory bulb, ventral-lateral and later al parts of the dorsal telencephalon (homologue of the mammalian hippocampu s), ventral area of the telencephalon (homologue of the mammalian amygdala) , glomerulosus complex of the thalamus, the preoptic area, and inferior lob e of the hypothalamus. The pattern of GRir neuronal distribution in sexuall y immature and spawning fish was similar. However, spawning fish brains, co mpared to sexually immature brains, exhibited a significantly greater GRir neuronal number in several olfactory regions in paired immunohistochemical runs. There also were differences in intraneuronal location of GRir in olfa ctory regions, with staining being predominantly cytoplasmic in sexually im mature fish but nuclear in spawning fish. These results are consistent with a role for cortisol in olfactory-mediated homing in kokanee salmon. Althou gh GRir were identified in many nonolfactory regions, the focus of this stu dy is on GRir present in brain regions involved in olfaction. (C) 2000 Acad emic Press.