ROLES OF NEUROTRANSMITTERS IN REGULATING REPRODUCTIVE HORMONE-RELEASEAND 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, U ca 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 g anglia. 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 produce d 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 matur ation 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 h ormone, resulting in testicular maturation. In contrast, dopamine (DA) inhibits gonadal maturation in both sexes. Methionine enkephalin, lik e DA, slows ovarian maturation. Red pigment-concentrating hormone (RPC H), like 5-HT, stimulates ovarian maturation both in vivo and in vitro , apparently by stimulating GSH release. RPCH does not affect the ovar y directly. Calcium appears to act here as a second messenger for RPCH . The implications of these findings for enhancing the culture of crus taceans is discussed.