Larval metamorphosis in four bivalve species in response to NMDA receptor ligands: The NMDA receptor pathway as potential regulator of bivalve transition to spat

Bivalves are NO Different: Nitric Oxide as Negative Regulator of Metamorphosis in the Pacific Oyster, Crassostrea Gigas.

“…Larvae exposed in January 2018 and March 2019 ( Figure 3A & 3B) were successfully induced with EPI and MK-801 as well as L-DOPA and ifenprodil (C. gigas 2018) and the NO pathway inhibitors SMIS, AGH, 7-NI and ODQ (C. gigas 2019). Comparison between larval batches in December 2018 and March 2019 indicates that the response to NO pathway inducers is also cohort dependent, as we have previously suggested for the NMDA receptor related compounds, MK-801 and ifenprodil (2). Experiments conducted in March 2019 displayed lower metamorphosis percentages relative to experiments using larvae from December 2018 ( Figure 1) Figure 3B).…”

“…During exposure and nal assessment of larvae and spat, several noteworthy behaviour differences were observed between treatments. During EPI and MK-801 exposure larvae are generally immobile on the bottom, and spat induced with EPI are unattached, while MK-801 spat are partially attached and unattached as previously shown (2). Some of those bottom laying larvae showed visible contractions of the larval organs -a behaviour often seen few hours after start of exposure to EPI, and might suggest larvae were undergoing metamorphosis.…”

“…The opening of the receptors causes an in ow of Ca 2+ leading to an increase in the intracellular Ca 2+ concentration, which in turn generates downstream responses such as activation of enzymes, gene regulation, or other cell-speci c responses (reviewed in (5)). We demonstrated previously that exposure of competent larvae of different oyster and clam species to MK-801, a NMDA receptor speci c channel blocker, signi cantly induced metamorphosis in these species (2). Cloning and characterisation of NMDA receptors in the Paci c oyster Crassostrea gigas as well as localisation of NMDA receptor subunit 1, CgNR1, in key structures of competent larvae such as the apical sensory organ (ASO), the underlying apical/cerebral ganglia and the nerve network of the foot (4), established the existence of functional NMDA receptors in bivalve nervous systems.…”

“…All metamorphosis assays were conducted following a general protocol as previously described (2)(3)(4). In brief, competent pediveliger larvae (shell length 300-330 µm, visible eyespot, crawling behaviour) were placed in FSW in glass shell vials, continuously exposed to chemical compounds for either 1 h, 3 h, 6 h or 24 h; the chemicals were then removed by pipetting, and 10 ml FSW including microalgae was added to each vial.…”

“…Complex neuroendocrine pathways and neurotransmitters have been proposed as regulators for metamorphosis in bivalves (reviewed in (1)), but there are many unknown factors regulating this process. Recently, we provided evidence for a previously unexplored regulatory pathway involved in bivalve metamorphosis involving the transmembrane N-Methyl-D-aspartate (NMDA) receptor (2)(3)(4). As ligand-gated and voltage-dependent ion channels, NMDA receptors are located in synaptic cell membranes and are activated by agonists, predominantly glutamate, co-agonists (e.g.…”