Effects of serotonin, GABA and neuropeptide Y on seabream gonadotropin releasing hormone release in vitro from preoptic-anterior hypothalamus and pituitary of red seabream, Pagrus major.

The effects of serotonin (5-HT), GABA and neuropeptide Y (NPY) on in vitro release of seabream (sb) gonadotropin releasing hormone (GnRH) from slices of the preoptic-anterior hypothalamus (P-AH) and pituitary of red seabream were studied. 5-HT, GABA and NPY all stimulated the release of sbGnRH from the P-AH but not from the pituitary of immature red seabream. They also stimulated sbGnRH release from the P-AH with a similar potency during the course of gonadal development. Specific agonists and/or antagonists of 5-HT, GABA and NPY showed that 5-HT and GABA utilize 5-HT(2) and GABAA receptor subtypes, respectively, to mediate their action, and that NPY employs at least NPY(Y1) and NPY(Y2) receptor subtypes to stimulate sbGnRH release. Combinations of different antagonists for 5-HT, GABA and noradrenaline/adrenaline did not block the stimulatory influence of NPY on release of sbGnRH, indicating that the action of NPY on the sbGnRH neuronal system is probably direct.