Alterations in gonadotropin-releasing hormone immunoactivities in discrete brain areas of male goldfish during spawning behavior.

In male goldfish, spawning behavior and gonadotropin (GtH) secretion are stimulated during exposure to females which were induced to perform spawning behavior by treatment with prostaglandin F2 alpha (PG). In this study, exposure to PG-treated females for 1 or 2 h significantly increased serum GtH levels, and GtH-releasing hormone (GnRH) concentrations in the olfactory bulbs, telencephalon and hypothalamus, indicating that spawning behavior can influence cellular events of the brain GnRH neuronal system and pituitary GtH secretion in male goldfish. To study the role of the olfactory system in the hormonal responses to PG-treated females, bilateral sectioning of olfactory tracts (OTX), medial (mOTX) or lateral (lOTX) olfactory tract were carried out in male goldfish. Both OTX and mOTX, but not lOTX, blocked the behavioral response of male goldfish to PG-treated females and abolished the increases in serum GtH and brain GnRH levels, suggesting that alterations in pituitary GtH secretion and brain GnRH levels are associated with a pheromonal activation of spawning behavior through the medial olfactory tracts in male goldfish. This behavioral activation of the GnRH neuronal system provides a useful physiological model for studying the regulation of GnRH system in male goldfish.