Species-specific effects on hemolymph glucose control by serotonin, dopamine and L-enkephalin and their inhibitors in Squilla mantis and Astacus leptodactylus (Crustacea)

Hemolymph glucose level is controlled by crustacean Hyperglycemic Hormone(cHH) released from the eyestalk neuroendocrine centers under conditions of both physiological andenvironmental stress. Biogenic amines and enkephalin have been found to mediate the release ofseveral neurohormones from crustacean neuroendocrine tissue. We investigated the effect ofserotonin, dopamine, and Leucine-enkephalin in vivoFinjected into the stomatopod Squilla mantisand the decapod Astacus leptodactylusFwhether increasing or depressing glycemia. Serotonin had amarked effect in elevating glucose level compared with initial values in both species. 5–HT1–likereceptors are more involved in mediating serotonin action as co-injected cyproheptadine was a moreeffective antagonist than ketanserin (5–HT2–like receptor inhibitor). Dopamine injection in intactanimals produced a decrease below initial levels of hemolymph glucose. This effect was significantlyantagonized by domperidone. No significant effect of both amines occurred in eyestalkless animals.L-enkephalin shows a differential effect: in S. mantis it induced hypoglycemia while in A.leptodactylus it caused an increase of glucose level. Co-injected antagonist naloxone affected thedirection of the response. Serotonin appears to provide a major control on glucose mobilization,whereas dopamine and L-enkephalin act as modulators whose plasticity in use or action variesamong species. J. Exp. Zool. 301A:727–736, 2004. r 2004 Wiley-Liss, Inc.