Afferent fibers of the vagus nerve carry TNF-induced neurograms. (A) (Top) Trace showing the spontaneous activity of the cervical vagus nerve. (Bottom) Trace showing the injection of TNF (dose of 50 µg, marked by line). (B) Graph depicting the frequency of CAP firing for the control and TNF-induced neurograms (shown in A). The 10-min period immediately after TNF injection is used to calculate CAP firing, as well as the equivalent period from the baseline. (C) Diagrams of the surgical vagotomies employed to test the direction of flow of the TNF-induced neurogram. A proximal (Prox) cut between the electrodes and the brain isolates the sensory component, while a distal cut isolates the efferent arm. (D) Graph showing the frequency of CAP firing in 60-s bins (mean ± SEM, line ± shaded area) starting 10 min prior to TNF injection (dose of 50 µg) at time zero. Data represent N = 3 for each of proximal (filled circles) and distal (open circles) vagotomies. (E) Plot showing mean CAP frequencies for the 10-min periods before and right after TNF in individual mice. The distal cut completely abolishes the TNF effect, which is not affected by the proximal cut (P = .03 for post values, t test), indicating that afferent fibers are required.