Regulation of fish phagocytic functions by hormones and neurotransmitters

社会应激下下属罗非鱼血浆皮质醇水平显著升高，抑制了下属罗非鱼的中性粒细胞防御活动（呼吸爆发和吞噬）。中性粒细胞在含有皮质醇的培养基中培养，其防御活动受损。由此可见，皮质醇可直接影响中性粒细胞的活性。组织驻留的嗜酸性颗粒细胞（EGCs），其中可能包括中性粒细胞迁移因子(s)，也受到皮质醇的不利影响。应激条件下，皮质醇对EGC脱颗粒活性的损害可能与中性粒细胞向炎症部位迁移的减少有关。这些受损的非特异性防御机制可能会增加对感染的易感性，并使感染在应激鱼中传播。事实上，植入皮质醇的罗非鱼对迟发爱德华氏菌感染的易感性更高。与皮质醇（另一种应激激素）相比，β内啡肽在体内和体内增强虹鳟头肾吞噬细胞的防御活性。β内啡肽对体外培养的鲤鱼头肾白细胞也有刺激作用。结果表明，应激激素主要有两种类型：抑制吞噬细胞激素和促吞噬细胞激素。作为一种神经递质，肾上腺素在体外降低了中性粒细胞的防御活性。肾上腺素β受体可能与这种抑制作用有关，肾上腺素β受体拮抗剂心得安可阻断肾上腺素对中性粒细胞的不良作用。血清素，另一种神经递质，也能抑制罗非鱼体外中性粒细胞的呼吸爆发。这些结果表明，鱼类的防御系统与神经系统密切相关。

Plasma cortisol level of subordinate tilapia under social stress increased significantly, and neutrophil defense activities (respiratory burst and phagocytosis) from the subordinate fish were suppressed. Neutrophils incubated in a medium containing cortisol were impaired in their defense activities. From these results, cortisol could affect the neutrophil activities directly. Tissue-resident eosinophilic granular cells (EGCs), in which neutrophil-migrating factor (s) could be included, were also adversely affected in their degranulation by cortisol. Impaired EGC degranulating activity by cortisol could be involved in less migration of neutrophils to the inflammatory site under stressful conditions. These impaired non-specific defense mechanisms could increase susceptibility to infections and allow the infections to spread in the stressed fish. In fact, cortisol-implanted tilapia had higher susceptibility to Edwardosiella tarda infection.In contrast to cortisol, another stress hormone, β endorphin enhanced defense activities of head kidney phagocytes from rainbow trout in vivo and in vivo. Carp head kidney leucocytes also were stimulated by β endorphin in vitro. It is indicated that there are two types of stress hormones, phagocyte-inhibiting hormone and phagocyte-stimulating hormone.A neurotransmitter, adrenarin reduced the neutrophil defense activities in vitro. Adrenarin β receptor could be associated with this inhibition, with propranolol, antagonist of adrenarin β receptor, blocking the adverse effect of adrenarin on neutrophils. Serotonin, another neurotransmitter, also suppressed respirator burst of tilapia neutrophils in vitro. From these results, it is suggested that fish defense system is closely related with the nervous system.