Immunoneutralization of gonadotropin-releasing hormone type-III suppresses male reproductive behavior of cichlids.

To investigate the roles of gonadotropin-releasing hormone (GnRH) types in reproductive behaviors, antisera against GnRH1, GnRH2 and GnRH3 were stereotaxically administered into the intracerebroventricular region to neutralize the three native GnRH types in the brain of male tilapia Oreochromis niloticus. Reproductive behaviors (nest-building and aggressive behaviors), and morphological changes of the three GnRH systems were investigated by immunocytochemistry. GnRH1, GnRH2 and GnRH3 immunoreactive fibers were significantly decreased following injections of GnRH antisera indicating successful neutralization of their respective endogenous GnRH peptides. GnRH1- and GnRH2-immunoneutralization did not inhibit reproductive behaviors but GnRH3-immunoneutralization significantly decreased nest-building ability (Saline: 26.5 +/- 3.7%/day versus GnRH3: 6.1 +/- 2.9%/day, P < 0.001), nest size (Saline: 0.67 +/- 0.09 points versus GnRH3: 0.10 +/- 0.05 points, P < 0.0002) and aggressive behavior (Saline: 2.34 +/- 0.19 points versus GnRH3 1.06 +/- 0.12 points, P < 0.0001). These observations provide evidence that GnRH3 is a potent neuromodulator of reproductive behaviors in male tilapia.