MC4R and type 2 diabetes mellitus: 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.