Roles of neurotransmitters in regulating reproductive hormone release and gonadal maturation in decapod crustaceans

Experiments done in this laboratory showed 5-hydroxytryptamine (5-HT) stimulates gonadal maturation in male and female sand fiddler crabs, Uca pugilator, and red swamp crayfish, Procambarus clarkii. This action of 5-HT is indirect, 5-HT apparently stimulating release of the gonad-stimulating hormone (GSH) that is present in the brain and thoracic ganglia. For example, studies with ovarian explants showed 5-HT has no direct effect on the ovary. But, when ovarian explants were incubated with 5-HT and brain or thoracic ganglia, the incubation medium produced greater ovarian maturation than did the medium when ovarian explants were incubated with brain or thoracic ganglia alone, 5-HT presumably enhancing GSH release. In males 5-HT not only induces testicular maturation but also development of the androgenic glands. 5-HT in males, as in females, apparently triggers GSH release; but in males GSH in turn stimulates the androgenic glands which release the androgenic gland hormone, resulting in testicular maturation. In contrast, dopamine (DA) inhibits gonadal maturation in both sexes. Methionine enkephalin, like DA, slows ovarian maturation. Red pigment-concentrating hormone (RPCH), like 5-HT, stimulates ovarian maturation both in vivo and in vitro, apparently by stimulating GSH release. RPCH does not affect the ovary directly. Calcium appears to act here as a second messenger for RPCH. The implications of these findings for enhancing the culture of crustaceans is discussed.