Dopaminergic regulation of brain gonadotropin-releasing hormone in male goldfish during spawning behavior.

Dopaminergic regulation of gonadotropin-releasing hormone (GnRH) concentrations in discrete brain areas of male goldfish was studied using the centrally active dopaminergic agonist apomorphine and antagonist pimozide. Pimozide caused time- and dose-dependent increases in serum gonadotropin levels and accumulation of GnRH in the olfactory bulbs, telencephalon and pituitary. The effects of pimozide were partially antagonized by apomorphine, which, when given alone, did not influence basal levels of brain GnRH and serum gonadotropin, but inhibited the increases in brain GnRH and serum gonadotropin levels that normally occur in response to spawning stimuli from prostaglandin-treated females. To study the physiological significance of the accumulation of brain GnRH due to central dopaminergic receptor blockade, the influences of pimozide on the brain GnRH and serum gonadotropin responses of male goldfish to spawning stimuli were tested. Pimozide pretreatment potentiated the serum gonadotropin increases and caused a marked reduction in the GnRH levels in olfactory bulbs, telencephalon and pituitary in response to spawning stimuli. These findings demonstrate that the central dopaminergic system is an important inhibitory component in the regulatory circuitry of brain GnRH levels in normal and behaviorally stimulated male goldfish.