MTOR and obesity due to melanocortin 4 receptor deficiency: mTOR has been found to be over-expressed in obesity-linked insulin resistance in mice (Khamzina et al., 2005; Tremblay et al., 2007) and to be upregulated by chronic lipid availability in rats, which could be reversed by exercise training leading to AMPK activation (Rivas et al., 2009).