Effects of GABA receptor antagonists bicuculline and CGP52432 on larval settlement and metamorphosis of the mussel (Mytilus coruscus)

γ-aminobutyric acid (GABA) is an important inhibitory neurotransmitter in the central nervous system in mammals. In marine invertebrates, GABA has been reported to induce larval settlement and metamorphosis in many species. The pharmacological experiment was conducted to study the effects of GABA and its receptor inhibitors Bicuculline (GABA_A receptor) and CGP52432 (GABA_B receptor) on larval settlement and metamorphosis of M. coruscus. GABA receptor-associated protein (GABARAP) and GABA_B2 receptor (GABA_B2R) genes have been found in the transcriptome data of different developmental stages of M. coruscus. GABA_B2R was significantly highly expressed in the pediveliger stage than in other development stages. A similar expression pattern was also observed using the real-time fluorescent quantitative PCR experiment, suggesting that GABA_B2R may be involved in the larval metamorphosis. The results showed that 10^-4 mol/L GABA induced 27.2%±3.0% of the pediveliger larvae metamorphosis. Bicuculline and CGP52432 significantly inhibited larval metamorphosis compared to the control larvae. The higher concentrations of antagonists showed more pronounced effects than lower concentrations. In addition, both GABA and its receptor antagonists inhibited the swimming behavior of mussel larvae. Both GABA_A and GABA_B receptor antagonists inhibited the larval settlement and metamorphosis of M. coruscus, suggesting GABA receptors may be involved in mediating larval settlement and metamorphosis of M. coruscus. The present study contributes to further exploring the mechanism of the GABAergic signaling system regulating larval settlement and metamorphosis of M. coruscus.