The behavioral thermoregulatory response of febrile female rats is not attenuated by vagotomy

An oft-overlooked consequence of fever is the occurrence of thermoregulatory heat-seeking/producing behaviors. Subdiaphragmatic vagotomy attenuates fever resulting from low dose, peripherally administered pyrogens, suggesting that the vagus is involved in generating the pathogen-induced rise in core body temperature (Tc). This study was designed to confirm that rats utilize behavioral thermoregulation to augment fever following systemic administration of lipopolysaccharide (LPS), and to test the hypothesis that, in febrile animals, vagotomy would block the preference for a higher ambient temperature (Ta) as Tc is rising. First, female Sprague-Dawley rats received IP injections of either saline or LPS (50 μg/kg), prior to placement inside a thermal gradient that offered subjects Ta values between 7 and 45 °C. LPS injection caused significant increases in Tc and selection of a higher Ta as compared to saline administration. Second, groups of rats were vagotomized, sham-vagotomized or received no surgery, and then underwent the same gradient testing procedure. Vagotomy attenuated LPS-induced fever, but did not influence the concomitant behavioral thermoregulatory response. All groups selected comparable, higher Ta values following LPS vs. saline. These data suggest that the reduction in the febrile response to LPS administration following vagotomy is not due to inhibition of the behavioral thermoregulatory response to the pyrogen. Rather, this behavioral response to LPS appears to be mediated by a nonvagal mechanism.