Physiological involvement of DA in ovarian development of the freshwater giant prawn, Macrobrachium rosenbergii

Biogenic amines such as dopamine (DA) and serotonin (5-hydroxytryptamine, 5-HT) are able to affect numerous physiological processes in crustaceans through their actions as neuroregulators. Both DA and serotonin have been shown to be involved in the synthesis and release of neurohormones such as crustacean hyperglycemic hormone (CHH), vitellogenesis-inhibiting hormone (VIH), molt-inhibiting hormone (MIH) and those related to pigmentation which in turn subsequently influence homeostasis and homeokinesis. The effect of DA and 5-HT on the ovarian development of the freshwater giant prawn, Macrobrachium rosenbergii, as well as the pathway of these actions is presented in this paper. During a 20-day experimental period, hemolymph was collected from both intact and bilaterally eyestalk-ablated prawns 2 days after each administration of DA and 5-HT which was injected into the prawns on every fourth day. The vitellogenin concentration in the hemolymph was then quantified using ELISA technique. The results show that DA depressed vitellogenin synthesis while 5-HT enhanced the process. When DA was injected with selective receptor antagonists, SCH23390, a DA D 1 receptor antagonist, was able to suppress DA's effect on vitellogenin synthesis while domperidone, a DA D 2 receptor antagonist, had no apparent effect, suggesting that the actions of DA are primarily channeled through D 1 receptor. Given that DA is able to inhibit vitellogenin synthesis in eyestalk-ablated prawns in a similar manner as in intact prawns, it is clear that the inhibitory action of DA is at the thoracic ganglia through inhibition of vitellogenesis-stimulating hormone (VSH) release, but not at the eyestalk level through stimulation of VIH release from the X organ–sinus gland complex.