Interleukin-6 and tumor necrosis factor-α attenuate dopamine release in mice fed a high-fat diet, but not medium or low-fat diets

Chronic low-grade inflammation is associated with a state of diet-induced obesity that impacts systemic tissues and can cross the blood-brain barrier to act directly on the brain. The extent to which pro-inflammatory cytokines released in these conditions affect dopamine presynaptic neurotransmission has not been previously investigated. The purpose of this study was to examine how dopamine terminals are affected by pro-inflammatory cytokines, and to determine if dietary fat consumption potentiates cytokine effects on dopamine release and reuptake rate in the nucleus accumbens (NAc). Male and female C57BL/6J mice were fed high, medium, or low-fat diets (60%, 30%, or 10% total kcals from fat, respectively) for six weeks. Fast scan cyclic voltammetry (FSCV) was used to measure dopamine release and reuptake rate in the NAc core from ex vivo coronal brain slices. Electrically evoked dopamine release and the maximal rate of dopamine reuptake (V-max) were significantly lower in mice fed the 30% and 60% high-fat diets compared to the 10% low-fat group (p < 0.05). IL-6 5 or 10 nM or TNF alpha 30 or 300 nM was added to artificial cerebrospinal fluid (aCSF) bathed over brain slices during FSCV. No effect on dopamine release or V-max was observed with lower concentrations. However, 10 nM IL-6 and 300 nM TNF alpha significantly reduced dopamine release in the 60% fat group (p < 0.05). No effect of added cytokine was observed on V-max. Overall, these data provide evidence that dietary fat increases neural responsiveness to cytokines, which may help inform comorbidities between diet-induced obesity and depression or other mood disorders.