Synergistic Effects of Interleukin-1β, Interleukin-6, and Tumor Necrosis Factor-α: Central Monoamine, Corticosterone, and Behavioral Variations

Abstract

The proinflammatory cytokines interleukin-1β (IL-1β), IL-6, and tumor necrosis factor-alpha (TNF-α) influence neuroendocrine activity, promote central neurotransmitter alterations, and induce a constellation of symptoms collectively referred to as sickness behaviors. These cytokines may also elicit anxiety and anhedonia, and have been associated with psychological disturbances in humans. In the present investigation, systemic IL-1β and TNF-α dose-dependently and synergistically disrupted consumption of a highly palatable food source (chocolate milk), possibly reflecting anorexia or anhedonia engendered by the treatments. As well, these cytokines synergistically increased plasma corticosterone levels. Although IL-1β and TNF-α provoked variations of amine turnover in the hypothalamus, locus coeruleus, and central amygdala, synergistic effects were not evident in this respect. Nevertheless, in view of the central amine variations induced by the cytokines, it is suggested that immune activation may come to influence complex behavioral processes, as well as affective state.