LEP and major depressive disorder: Leptin has antidepressant effects when administered into the hippocampus, an area mediating cognitive impairments of depression whereas genetic deletion of hippocampal LepRb results in a depression-like phenotype (Asakawa et al., 2003; Lu et al., 2006; Finger et al., 2010; Liu et al., 2010a; Guo et al., 2013).