IN-VIVO EFFECTS OF DOPAMINE AND DOPAMINERGIC ANTAGONISTS ON TESTICULAR MATURATION IN THE RED SWAMP CRAYFISH, PROCAMBARUS-CLARKII

In vivo, dopamine (DA) inhibits testicular maturation in the red swamp crayfish, Procambarus clarkii. Crayfish given DA injections had a sma ller testicular index, smaller testicular lobes, fewer mature sperm, a nd less-well-developed androgenic glands than did the control crayfish given physiological saline. Males administered 5-hydroxytryptamine (5 -HT) or a DA receptor blocker, spiperone or pimozide, showed enhanced testicular maturation and more highly developed androgenic glands than did the control crayfish. When equimolar amounts of 5-HT and DA were co-injected, the actions of DA and 5-HT were found to be antagonistic. These results can be explained by assuming not only that 5-HT trigger s release of the gonad-stimulating hormone (GSH) but that DA (a) trigg ers release of the gonad-inhibiting hormone (GIH), (b) inhibits GSH re lease, or (c) does both (a) and (b), with GSH and GIH affecting the an drogenic glands directly, thereby regulating release of the androgenic gland hormone that has the well-established role of stimulating testi cular maturation and spermatogenesis.