Effects of naloxone, serotonin, and dopamine on reproduction of the freshwater crab Barytelphusa guerini

Several investigators suggest a relationship between neurotransmitters, serotonin (also called 5-hydroxytryptamine, 5-HT), and dopamine (DA) in the regulation of growth and reproductive development of vertebrate species, rather than the invertebrate species. In this study, we evaluated the role of 5-HT and DA in reproductive development of an invertebrate species, the freshwater crab Barytelphusa guerini. We tested the effects of 5-HT both alone and combined, and also the effects of an opioid antagonist naloxone, on reproductive development of B. guerini in terms of testicular and ovarian developmental parameters. Injection of either 5-HT or naloxone alone significantly increased the ovarian index and the oocyte diameter in female crabs, and the testicular index and testicular follicular diameter in male crabs. In contrast, injection of DA inhibited all the reproductive measures in both sexes. Co-injection of 5-HT with DA exhibited no significant effects on the reproductive development in both sexes compared to the control treatments. These results suggest that 5-HT, DA, and exogenous naloxone may be involved in the regulation of gonad stimulating hormone (GSH) and/or gonad inhibiting hormone (GIH). These results also provide evidence that naloxone may regulate endogenous neurotransmitters and its downstream hormones, GSH and GIH. J. Exp. Zool. 321A: 173-182, 2014. (c) 2013 Wiley Periodicals, Inc.