Corticotropin-releasing hormone (CRH) in the teleost fish Oreochromis mossambicus (tilapia): in vitro release and brain distribution determined by a novel radioimmunoassay

Abstract

The quantitative distribution of corticotropin-releasing hormone (CRH) in the brain and pituitary of the fish Oreochromis mossambicus (tilapia) was studied following the validation of a radioimmunoassay. Compared to the pituitary content, the brain contained 20 times more CRH. Eighty percent of the total brain content was located outside the hypothalamus, particularly in the telencephalon. Substantial amounts of CRH were also present in other regions devoid of hypophysiotropic neurons, such as the vagal lobe and optic tectum. Telencephalic and pituitary CRH co-eluted with the tilapia CRH 1–41standard on reverse phase HPLC. In vitro CRH release by the telencephalon amounted to 5% of its content per hour, whereas release from the pituitary was negligible. We conclude that CRH in the brain of tilapia regulates pituitary and non-pituitary related functions, probably as a neurotransmitter or neuromodulator.