Effects of histamine on the neuroendocrine-immune regulatory network in the Pacific white shrimp, Litopenaeus vannamei

In shrimp culture, feed made from stale fishmeal and decomposition of dead shrimp easily produces large amounts of histamine in the water environment, which will cause disease outbreaks. Simultaneously, in the internal environment of crustaceans, histamine is a short-acting biogenic amine that can act as a neurotransmitter and regulate immunity. To investigate the effects of histamine on the neuroendocrine-immune network of crustaceans, a histamine injection experiment was carried out on Litopenaeus vannamei in this study. The results showed that the neuroendocrine factors, including hormones (corticotrophin-releasing hormone, adrenocorticotropic hormone) and biogenic amines (dopamine, noradrenaline), in the histamine injection groups increased significantly at 6 h, while the 5-hydroxytryptamine concentration was significantly decreased at 12 h. The intracellular signaling pathways, including the PKC pathway (phospholipase C, diacylglycerol and protein kinase C), the RAP1 pathway (RAS-associated protein and integrin α_IIbβ₃), the PI3K/PKB pathway (phosphoinositide 3-kinase, phosphatidylinositol (3,4,5)-trisphosphate and protein kinase B) and the MAPK pathway (rat sarcoma protein and extracellular signal-regulated kinase) in the histamine injection groups all decreased significantly after 6 h and shared a similar trend. The immune parameters, including total hemocyte count, cell viability, phagocytic activity, phenoloxidase activity of hemocyte, antibacterial activity, bacteriolytic activity and hemagglutinating activity, all decreased significantly in the histamine injection group after 6 h, while phenoloxidase activity of plasma increased significantly. In addition, the antioxidant parameters (superoxide dismutase, catalase and glutathione peroxidase) in the histamine injection group were significantly increased. These results indicated that histamine might regulate the prophenoloxidase system via the PKC pathway, further influence the antibacterial and bacteriolytic activities, regulate hemagglutinating activity via the PKC-RAP1 pathway, regulate the total hemocyte count and cell viability via the PKC -PI3K/PKB pathway, and regulate phagocytic activity via the PKC -PI3K/PKB -MAPK pathway. Meanwhile, histamine may also affect the activities of antioxidant enzymes via the RAP1 pathway and the PKC-PI3K/PKB pathway. Therefore, it may be concluded that the neuroendocrine-immunoregulatory network plays a principal role in histamine regulation and causes immune and antioxidant defense in L. vannamei.