First report of a putative involvement of the NMDA pathway in Pacific oyster (Crassostrea gigas) development: Effect of NMDA receptor ligands on oyster metamorphosis with implications for bivalve hatchery management

In bivalve aquaculture, the use of neurotransmitters such as epinephrine (a catecholamine) to induce settlement and metamorphosis in hatcheries is a common practice in some species, but the actual neuroendocrine pathways involved in bivalve metamorphosis are not well understood. In vertebrates, the N-methyl-d-aspartate (NMDA) receptor, a ligand-binding, ion-channel transmembrane receptor, is known to regulate the production and release of catecholamine, but the role of NMDA receptors has not been explored in relation to bivalve metamorphosis. In this paper we investigate the effect of known NMDA receptor interacting compounds on metamorphosis in the Pacific oyster Crassostrea gigas. Our results demonstrate that ifenprodil and MK-801 - specific antagonists to the NMDA receptor - affect metamorphic processes in Pacific oysters, with up to 50% increase in spat production after 3 h exposure, thus indicating a relationship between the NMDA pathway activation and oyster metamorphosis. In addition, metamorphosis was induced by the application of chlorpromazine, a non-selective antagonist to the NMDA receptor. These findings indicate a putative regulatory function of the NMDA pathway in Pacific oyster metamorphosis, providing a potential new direction for the development of new and better inducers for metamorphosis in cultivated bivalve species, particularly in cases wherein catecholamines cannot be applied effectively for hatchery applications.