THE REGULATORY EFFECTS OF NEUROENDOCRINE FACTORS ON GONADOTROPIN-RELEASING HORMONE (GnRH) RELEASE FROM HYPOTHALAMUS AND PITUITARY OF JUVENILE AND ADULT COMMON CARP (CYPRINUS CARPIO) IN VITRO.

In juvenile fish, DA significantly stimulates GnRH release from hypothalamus slices and pituitary fragments in a dose-response relation but TRH and GABA have no effects. In yearling sexually regressed fish, DA significantly inhibits GnRH release from hypothalamus slices and pituitary fragments in a dose-response relation, whereas TRH and GABA stimulate GnRH release. DA also inhibits GABA-stimulated GnRH release. When TRH in combination with GABA, the GnRH release from hypothalamus slices and pituitary fagments is much less than that of TRH and GABA alone, both in juvenile and yearling common carp. This result implies that there may exist an inter-inhibitory action on GnRH release between TRH and GABA.