TNF and major depressive disorder: These vagal mediated immune signals contribute to multiple functions, such as peripheral IL-1 and LPS-induced depression (Bluthe et al., 1994, 1996; Luheshi et al., 2000), IL-1β and LPS-induced inhibition of food-motivated behavior (Bret-Dibat et al., 1995), endotoxin, IL-1 and TNF-induced hyperalgesia (Watkins et al., 1994, 1995), and bacterial endotoxin, TNF and IL-1β-induced activation of the HPA axis (Gaykema et al., 1995; Fleshner et al., 1998).