NPY and obesity due to melanocortin 4 receptor deficiency: Indeed, MRAP2-knockout mice had reduced fasting-induced activation of AGRP neurons (decreased cFos activity and failure to induce Agrp and neuropeptide Y (Npy) gene expression); while mice with specific deletion of MRAP2 from AGRP neurons failed to develop obesity and ate significantly less after a 24-h fast (Srisai et al. 2017).