Immunocytochemical localization of sGnRH and cGnRH-II in the brain of goldfish, Carassius auratus.

The immunocytochemical distribution of salmon gonadotropin-releasing hormone (sGnRH) and chicken GnRH-II (cGnRH-II) neurons in the brain of goldfish was examined using respective antisera. Salmon GnRH-immunoreactive (ir) cell bodies were localized in the area between the olfactory nerve and the olfactory bulb (the terminal nerve ganglion), the ventral telencephalon, the preoptic area, and the hypothalamus. Chicken GnRH-II-ir cell bodies were observed in the same areas as were those of sGnRH, although the number of cell bodies were fewer than those of sGnRH. In addition, chicken GnRH-II-ir cell bodies were also observed in the midbrain tegmentum where no sGnRH-ir cell bodies were found. Both sGnRH-ir and cGnRH-II-ir fibers were distributed not only in the hypothalamus and the pituitary gland but also in various brain areas from the olfactory bulb to the spinal cord. The wide distribution of GnRH-ir fibers suggests that in the goldfish, sGnRH and cGnRH-II not only regulate gonadotropin release from the pituitary gland but also function as neuromodulators in various brain regions.