By contrast, wild-type mice maintained on a high-fat diet showed no increase in pSTAT3 positive cells in response to leptin (24.2±5.8 cells for vehicle versus 21.8±6.8 cells for leptin, p = 0.8), confirming that diet-induced obesity blunts the leptin-responsiveness of these first-order neurons. Here, LEP is linked to obesity due to melanocortin 4 receptor deficiency.