Obesity considerably elevates the odds of developing depression. Obesity in humans and murine models is characterized by a state of chronic low-grade inflammation including elevated circulating inflammatory cytokines, adipokines and triglycerides. Several lines of evidence implicate a neuroimmune etiology in a subset of depressed individuals; thus, persistent immune activation in obesity may give rise to mood impairments. As a neuroanatomical substrate integrating signals from diverse inputs, the nucleus accumbens (NAc) is implicated in the control of motivation and reward-seeking, the response to stress, and the regulation of anxiodepressive behavior.
Décarie-Spain, Sharma et al. sought to identify neuroinflammatory responses in the NAc and determine if they underlie anxiodepressive behavior provoked by diet-induced obesity. They investigated the impact of two isocaloric high fat diets (HFD), enriched either in palm oil (saturated) or olive oil (monounsaturated), on energy metabolism, immune activation, and anxiodepressive behavior in mice. Contrary to the largely protective effect of the monounsaturated HFD, they found a saturated HFD enhances weight gain, metabolic complications, systemic inflammation, and anxiety-like and despair responses in behavioral tests. Concurrently, the saturated HFD was found to increase the expression of several immune markers, trigger reactive gliosis, and stimulate NFκB transcriptional activity in the NAc.