Effects of interleukin-1 receptor antagonist on the behavioral effects of lipopolysaccharide in rat.

To investigate the role of interleukin-1 (IL-1) in lipopolysaccharide (LPS)-induced sickness behavior, rats were injected with recombinant human interleukin-1 receptor antagonist (IL-1ra), an endogenous cytokine able to block most of the biological effects of IL-1 both in vivo and in vitro. Intraperitoneal injection of IL-1ra (3 mg/rat) attenuated the depressive effect of LPS (250 micrograms/kg) on social exploration and body weight when both treatments were injected peripherally. Intracerebroventricular injection of IL-1ra (60 micrograms/rat) did not block the effects of peripherally injected LPS. These data indicate that the peripherally mediated effects of IL-1 account for a significant part of LPS-induced sickness behavior.