Preoptic norepinephrine mediates the febrile response of guinea pigs to lipopolysaccharide

Norepinephrine (NE) microdialyzed in the preoptic area (POA) raises core temperature (T(c)) via 1) alpha(1)-adrenoceptors (AR), quickly and independently of POA PGE(2), and 2) alpha(2)-AR, after a delay and PGE(2) dependently. Since systemic lipopolysaccharide (LPS) activates the central noradrenergic system, we investigated whether preoptic NE mediates LPS fever. We injected LPS (2 microg/kg iv) in guinea pigs prepared with intra-POA microdialysis probes and determined POA cerebrospinal (CSF) NE levels. We similarly microdialyzed prazosin (alpha(1) blocker, 1 microg/microl), yohimbine (alpha(2) blocker, 1 microg/microl), SC-560 cyclooxygenase (COX)-1 blocker, 5 microg/microl], acetaminophen (presumptive COX-1v blocker, 5 microg/microl), or MK-0663 (COX-2 blocker, 0.5 microg/microl) in other animals before intravenous LPS and measured CSF PGE(2). All of the agents were perfused at 2 microg/min for 6 h. T(c) was monitored constantly. POA NE peaked within 30 min after LPS and then returned to baseline over the next 90 min. T(c) increased within 12 min to a first peak at approximately 60 min and to a second at approximately 150 min and then declined over the following 2.5 h. POA PGE(2) followed a concurrent course. Prazosin pretreatment eliminated the first T(c) rise but not the second; PGE(2) rose normally. Yohimbine pretreatment did not affect the first T(c) rise, which continued unchanged for 6 h; the second rise, however, was absent, and PGE(2) levels did not increase. SC-560 and acetaminophen did not alter the LPS-induced PGE(2) and T(c) rises; MK-0663 prevented both the late PGE(2) and T(c) rises. These results confirm that POA NE is pivotal in the development of LPS fever.