GONADOTROPIN-RELEASING HORMONES OF TERMINAL NERVE ORIGIN ARE NOT ESSENTIAL TO OVARIAN DEVELOPMENT AND OVULATION IN GOLDFISH

The involvement of gonadotropin-releasing hormones (GnRHs) from the terminal nerve (TN) in ovarian development and ovulation was examined by olfactory tract section (OTX) in goldfish. After OTX, brain contents of salmon GnRH (sGnRH) and chicken GnRH-II (cGnRH-II) were measured by specific radioimmunoassays. Olfactory tracts of sexually maturing females were sectioned prior to the spawning season and were kept under natural conditions. Two months later, brain sGnRH contents markedly decreased in all brain areas (telencephalon, hypothalamus, optic tectum-thalamus, cerebellum, medulla oblongata) except in the olfactory bulbs, whereas cGnRH-II contents did not obviously change. Despite the large decreases in brain sGnRH contents, OTX and sham-operated female fish underwent vitellogenesis. Sexually mature OTX females could be stimulated to ovulate by increased water temperatures during spawning season. Brain sGnRH contents of these OTX fish also markedly decreased with no changes in cGnRH-II. It appears that sGnRH of TN origin, which comprises most of the brain sGnRH in the goldfish, is not a prerequisite for basal gonadotropin secretion and ovarian development, and is not likely to be related to the preovulatory gonadotropin surge which stimulates ovulation in goldfish. (C) 1994 Academic Press, Inc.