Reduced ingestion of sweetened milk induced by interleukin-1 and lipopolysaccharide is associated with induction of cyclooxygenase-2 in brain endothelia.

UNLABELLED

Previous studies have shown that interleukin-1 (IL-1) and lipopolysaccharide (LPS) administration to animals induces behavioral changes, including a reduction in feeding. These effects of IL-1 and LPS have been shown to be sensitive to inhibitors of cyclooxygenase (COX).

OBJECTIVES

To determine the relationships between induction of COX-2 in the brain with IL-1beta- and LPS-induced changes in body temperature, plasma corticosterone and feeding.

METHODS

Mice were injected with intraperitoneal doses of IL-1beta and LPS that decreased feeding. The induction of COX-2 was studied immunocytochemically in the brain, in parallel with core body temperature, the drinking of sweetened milk, and plasma concentrations of corticosterone.

RESULTS

COX-2 immunoreactivity (ir) was sparse in the brains of the untreated mice, but IL-1beta and LPS both increased its expression. This COX-2 induction appeared to be confined to blood vessels, and was not markedly region specific. Induction was evident 30 min after IL-1 or LPS, and was greater at 90 than at 30 min. COX-2-ir in the parenchyma did not change significantly. Thus induction of COX-2 occurred in brain endothelia in parallel with the reduction in feeding. This is consistent with the previously determined sensitivity of IL-1-induced changes in feeding to selective COX-2 inhibitors, and the responses to IL-1 in COX-2-deficient mice. The time courses of the IL-1- and LPS-induced increases in plasma corticosterone paralleled those in the reduction in milk drinking, however, the changes in body temperature appeared later.

CONCLUSIONS

Endothelial COX-2 may be involved in IL-1- and LPS-induced decreases in milk drinking, and possibly in the HPA axis activation. The decreased milk drinking may occur when IL-1 and LPS bind to receptors on brain endothelial cells subsequently inducing COX-2 and the production of prostanoids which elicit the reductions in milk drinking. Thus the behavioral effects of peripherally administered IL-1 and LPS appear to be mediated by multiple mechanisms, including endothelial COX-2, and vagal afferents.