SALMON GNRH SYNTHESIS IN THE PREOPTIC AREA AND THE VENTRAL TELENCEPHALON IS ACTIVATED DURING GONADAL MATURATION IN FEMALE MASU SALMON

Changes in salmon gonadotropin-releasing hormone (sGnRH) synthetic act ivity in the brain during gonadal maturation were examined by in situ hybridization in 2-year-old female masu salmon, Oncorhynchus masou. Du ring gonadal maturation, the numbers of neurons expressing sGnRH mRNA increased in the preoptic area and the ventral telencephalon, but not in the olfactory bulbs and the terminal nerve ganglion. The numbers of silver grains per neuron also increased in the preoptic area and the ventral telencephalon. These results indicate that sGnRH has multiple physiological functions according to the location of the neurons in th e brain. neurons in the preoptic area and the ventral telencephalon ar e involved in gonadal maturation possibly by stimulating gonadotropin synthesis and release, whereas neurons in the olfactory bulbs and the terminal nerve ganglion may have different roles. (C) 1995 Academic Pr ess, Inc.