NPY2R and obesity due to melanocortin 4 receptor deficiency: Some studies suggest that cold stress combined with HFD can trigger the release of neuropeptide Y (NPY) from sympatric neurons into adipose tissue, in turn upregulates NPY and its Y2 receptors (NPY2R) in a glucocorticoid-dependent manner in the abdominal fat, leading to increased fat content and obesity [26].