Subdiaphragmatic vagotomy does not block intraperitoneal lipopolysaccharide-induced fever

Several recent findings, including the inability of subdiaphragmatic vagotomy to block lipopolysaccharide (LPS)-induced interleukin-1β (IL-1β) protein in brain, have made it necessary to reexamine the role of the subdiaphragmatic vagal afferents in immune-to-brain communication. In this study, we examined the effects of intraperitoneal (i.p.) injections of LPS on core body temperature in control and subdiaphragmatically vagotomized rats. Vagotomized and sham-operated male Sprague–Dawley rats were injected i.p. with vehicle (pyrogen-free saline) on the control day and LPS (1, 10 or 50 μg/kg) on the experimental day, and core body temperature was monitored by telemetry for 6 h after the injection. At this time, rats were sacrificed, and serum, liver, and pituitary samples were collected. The i.p. injection of LPS increased core body temperature in both sham-operated and vagotomized rats compared to the saline injection. In addition, LPS significantly increased IL-1β levels in serum, liver, and pituitary compared to saline-injected controls. There were no significant differences in the magnitude of the fever or in the levels of IL-1β in serum, liver, or pituitary between sham-operated and vagotomized rats. Thus, the current data indicate that, at the doses tested, subdiaphragmatic vagal afferents are not crucial for i.p. LPS-induced fever. Because several effects of vagotomy have been shown to be dependent on dose, we are currently investigating whether vagal afferents are involved in lower-dose i.p. LPS-induced fever.