Vagotomy attenuates but does not prevent the somnogenic and febrile effects of lipopolysaccharide in rats.

The role of the vagus nerve in the somnogenic and pyrogenic effects of lipopolysaccharide (LPS) was studied in rats. Control rats (n = 8) and rats subjected to bilateral subdiaphragmal vagotomy (VX; n = 9) were injected with 100 micrograms/kg i.p. LPS at the beginning of the dark period. Sleep and brain temperature (Tbr) were recorded for 23 h after the injections. LPS caused increases in non-rapid eye movement sleep (NREMS) for 12 h after the injection in control rats. Sleep intensity, as indicated by the slow-wave activity (SWA) of the electroencephalogram during NREMS, was suppressed. LPS elicited biphasic Tbr responses: an initial hypothermia was followed by increases in Tbr that lasted for approximately 20 h. In vagotomized rats, the NREMS responses to LPS were blunted. The magnitude of the LPS-induced NREMS increases was about one-half of that seen in control rats, and these sleep responses lasted only for 6 h. LPS did not affect SWA in VX animals. VX completely abolished the hypothermic responses to LPS and shortened the duration of the hyperthermia. The results suggest that the subdiaphragmal vagi play an important, but not exclusive, role in the somnogenic and pyrogenic actions of intraperitoneally injected LPS.