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Abstract
The endogenous opioid system has been found to be involved in fever caused by pyrogens.
In the present study, we have investigated the role of the mu-opioid receptor in the
brain in fever induced by lipopolysaccharide. Rats were microinjected with 1 microg
of the mu-opioid receptor-selective antagonist, cyclic D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH(2)
(CTAP), into the preoptic anterior hypothalamus. Thirty minutes later, lipopolysaccharide
(50 microg/kg) was injected intraperitoneally (i.p.). CTAP reduced by 1 degrees C
the fever induced by lipopolysaccharide. However, it did not affect lipopolysaccharide
fever when it was given 3 h after lipopolysaccharide injection. These data indicate
that mu-opioid receptors within the preoptic anterior hypothalamus mediate the initiation
of lipopolysaccharide fever and suggest that the opioid system is involved in the
pathogenesis of fever in rats.