Actions of two forms of gonadotropin releasing hormone and a GnRH antagonist on spawning behavior of the goldfish Carassius auratus

The central effects of two native forms of gonadotropin-releasing hormone (GnRH), salmon GnRH (sGnRH) and chicken GnRH-II (cGnRH-II), and a GnRH antagonist, [Ac-delta 3-Pro(1), 4FD-Phe(2), D-Trp(3,6)]mGnRH (analog E), on the spawning behavior of sexually recrudescent female goldfish were investigated. The effects of analog E were also observed in mature males. Female spawning behavior was induced by intramuscular injection of females with prostaglandin F2 alpha and placing them in the presence of mature males. Behavioral responses were quantified by recording the numbers of spawning acts performed by each pair of fish for 2 h following brain intracerebroventricular (icv) injection of different dosages of peptide or saline as control. For males, the time spent courting the female was recorded. Each pair of fish was pretested to determine their level of spawning behavior, for comparison to spawning behavior following icy treatment. icy injection of analog E caused a significant decrease in the number of spawning acts performed by females, suggesting a role of endogenous GnRH in modulating female spawning behavior. icy injection of 0.5 ng/g of sGnRH or cGnRH-II significantly stimulated female spawning behavior, whereas doses of 1 ng/g and higher resulted in an almost complete inhibition of spawning, reflecting a down-regulation as a result of the excessive dosages. Analog E suppressed the actions of exogenous sGnRH and cGnRH-II on spawning behavior, as both the sGnRH- and cGnRH-II-induced increases in the number of spawning acts were inhibited by concomitant treatment with analog E. Analog E-injected males showed no alteration in courtship behavior. These results indicate that GnRH peptides play a major role in the control of female reproductive behavior in goldfish, but have little or no role in the control of male behavior. (C) 1999 Academic Press.