TNF and obesity due to melanocortin 4 receptor deficiency: When we consider areas important in cognition, in db/db mice, a model of metabolic syndrome where obesity arises as a result of leptin receptor insensitivity (Hummel et al., 1966), IL-1β, TNF-α, and IL-6 mRNA expression levels in the hippocampus are increased when compared to wild type controls (Dinel et al., 2011).