Differential Involvement of Central and Peripheral Norepinephrine in the Central Lipopolysaccharide‐Induced Interleukin‐6 Responses in Mice

: Intracerebroventricular injection of lipopolysaccharide (LPS) induces a marked increase in circulating interleukin (IL)‐6 levels and in IL‐6 mRNA expression in brain and peripheral organs. Recently, it was reported that intraperitoneal administration of α‐adrenoceptor antagonists inhibits centrally injected LPS‐induced increases in plasma IL‐6 levels, suggesting the involvement of the norepinephrine (NE) system in the central LPS‐induced IL‐6 response. However, the localization (either central or peripheral) of NE involvement in the central LPS‐induced IL‐6 response has not been characterized. In the present study, mice were pretreated with 6‐hydroxydopamine (6‐OHDA) administered intracerebroventricularly or intraperitoneally to deplete central or peripheral stores of NE, respectively. Intracerebroventricular LPS (50 ng/mouse) markedly increased plasma IL‐6 levels and IL‐6 mRNA expression in choroid plexus, hypothalamus, pituitary, adrenals, heart, liver, spleen, and lymph nodes, but with minimal effect in lung, kidney, and testis, as revealed by RT‐PCR. Pretreatment, with intracerebroventricular 6‐OHDA (50 μg/mouse) decreased the LPS‐induced plasma IL‐6 levels by 39% and the LPS‐induced IL‐6 mRNA expression in liver, spleen, and lymph nodes, but not in choroid plexus, hypothalamus, pituitary, adrenals, and heart. Pretreatment with intraperitoneal 6‐OHDA (100 mg/kg) decreased the LPS‐induced plasma IL‐6 levels by 36% and the LPS‐induced IL‐6 mRNA expression in all the peripheral organs displaying increased IL‐6 mRNA. Central LPS‐induced increase in plasma corticosterone levels was decreased slightly by central but not by peripheral NE depletion. These results suggest that central NE and peripheral NE are differentially involved in the central LPS‐induced IL‐6 mRNA expression in peripheral organs.