GABA-mediated neuroendocrine–immune regulation in Penaeus vannamei under low-salinity stress

GABA, an important inhibitory neurotransmitter that exhibits diverse biological functions, has been widely investigated for its immunomodulatory effects. However, its immunomodulatory mechanisms in Penaeus vannamei under low-salinity stress remain unclear. Penaeus vannamei was used as a model organism and subjected to dietary supplementation with 2.16 g/kg fucoidan for 60 days, combined with GAT1 gene knockdown via RNA interference and exposure to low-salinity stress. These findings indicate that GAT1 gene knockdown significantly reduces GABA concentration (from 3.48 ± 0.23 to 2.63 ± 0.21 mg/ml at 12 h). On the one hand, increased release of CRH and ACTH in the cerebral ganglion leads to secretion of neuroendocrine factors in the eyestalk. These factors bind to their respective receptors in plasma and intestines, influencing downstream signaling pathways to regulate hemocyte and intestinal immune homeostasis. On the other hand, GABA acts directly on hemocytes and the intestines to regulate downstream immune defense. In the hemocytes, THC, phagocytosis, agglutination, proPO, antibacterial and bacteriolytic activity were significantly decreased, whereas PO activity was significantly increased. Concurrently, intestinal immune factors were markedly reduced and intestinal histopathological damage was exacerbated. Furthermore, GAT1 interference significantly decreased antioxidant enzyme activity, leading to oxidative damage. This study systematically analyzed the molecular mechanism by which GABA regulates the immune response of Penaeus vannamei through the cerebral ganglion-eyestalk-hemocyte/intestine axis, and identified pattern recognition receptors and their downstream neurohormones as the key targets for precise immune enhancement intervention, providing new insights into sustainable shrimp aquaculture based on neuroimmune regulation under antibiotic-free conditions.