Although leptin and leptin receptors are abundantly expressed in the hippocampus, where they potentiate LTP in in vivo and in vitro experiments [159-162], conditions of elevated leptin concentrations, such as those observed in animal models of T2D [40], cause receptor resistance, abnormalities in signal transduction and impairments in synaptic plasticity [163]. This evidence concerns the gene LEPR and type 2 diabetes mellitus.