Central effects of leukotrienes on behavioral, physiological, and immunological responses in chicks

Arachidonic acid released from phospholipids in the cell membrane, is used to synthesize lipid mediators known as leukotrienes (LTs). LTs play a key role in numerous leukocyte functions including leukocyte migration and inflammation. However, their function in the avian central nervous system is poorly understood. Thus, this study investigated whether lipopolysaccharide (LPS) a cell wall component of Gram-negative bacteria modulates LT synthesis via 5-LOX, an LT synthase, in chicks (Gallus gallus). Intraperitoneal LPS injection substantially increased 5-LOX mRNA expression in the diencephalon, thymus, and bursa of Fabricius, but decreased its expression in the spleen. Subsequently, we investigated the main effects of LTs on behavioral, physiological, and immunological responses in chicks. Intracerebroventricular (ICV) injection of LTB₄ and LTC₄ did not affect food intake. Furthermore, ICV injection of LTB₄ and LTC₄ did not affect cloacal temperature, plasma constituents, or crop-emptying rate. ICV injection of LTB₄ considerably reduced the mRNA expression of inducible nitric oxide synthase (iNOS), cyclooxygenase (COX-2), interleukin-1β (IL-1β), and IL-6 in the diencephalon. However, expression of IL-8 mRNA was substantially increased by LTB₄. Similarly, LTC₄ injection notably decreased IL-1β mRNA expression in the diencephalon and tended to decrease COX-2 mRNA expression. This study suggests that LPS might affect the synthesis of LTs in the diencephalon, and these LTs might subsequently affect the diencephalic immune response in chicks.