Different receptor mechanisms mediate the effects of endotoxin and interleukin-1 on female sexual behavior

Activation of the immune system by lipopolysaccharide (LPS) produces physiological, neuroendocrine and behavioral effects, some of which are mediated by cytokine production. We have previously shown that the cytokine interleukin-1 (IL-1) inhibits sexual behavior in female, but not male rats, while producing a comparable suppression of locomotion in both sexes. The present study examined the effects of LPS on sexual behavior and locomotion of male and female rats, and the involvement of IL-1 receptors in mediating the effects of IL-1 and LPS on females behavior. Peripheral (i.p.) administration of LPS (50 or 250 μg/kg) significantly decreased sexual behavior in females, up to 6 h after administration, while it had no effect on male sexual behavior. However, locomotor activity, measured in the open- field test, was similarly reduced by LPS in both males and females. Pretreatment with the IL-1 receptor antagonist (IL-1ra) either i.p. (10 mg/kg) or intracerebroventricularly (i.c.v.) (50 μg/rat) did not prevent the inhibition of female sexual behavior and locomotion induced by either i.p. (50 μg/kg) or i.c.v. (200 or 400 ng/rat) administration of LPS, respectively. However, identical doses of IL-1ra significantly reversed the effects of IL-1β, administered either i.p. (5 μg/kg) or i.c.v. (50 ng/rat), respectively. These results demonstrate that both LPS and IL-1β produce marked inhibition of sexual behavior in female, but not in male rats. However, IL-1 receptors are not required for the effects of LPS on sexual behavior in female rats.