MC4R and obesity due to melanocortin 4 receptor deficiency: To this end, we tested whether either mice lacking the melanocortin 4 receptor (Mc4r; Mc4r−/−) or agouti (KK-Ay) mice (in which obesity and T2D (depending on the background strain) result from ectopic overexpression of Agouti, an Agrp homolog42) are resistant to the sustained antidiabetic response to icv FGF1 injection.