FAS and obesity due to melanocortin 4 receptor deficiency: To assess the effect of HFD-induced obesity on fatty acid synthesis we evaluated gene expression of fatty acid synthase (Fas)—a key enzyme catalyzing the synthesis of palmitate from malonyl coenzyme A. Fas expression in microglia from HFD-fed animals showed a lower expression at the end of the dark phase and higher expression at the beginning of the light phase, compared to control chow-fed animals (Figure 5I).