CCK and obesity due to melanocortin 4 receptor deficiency: In mouse Other studies in the ENS using mice models of high fat diet and obesity induced diabetic neuropathy reported a reduction in hormones such as ghrelin, cholecystokinin (CCK), and leptin levels; and inhibitory neurons expressing nitric oxide synthase (nNOS), vasoactive intestinal peptide (VIP), neuropeptide Y (NPY), and galanin as well as their expression levels (Chandrasekharan and Srinivasan, 2007; Li et al., 2011; Voukali et al., 2011; Stenkamp-Strahm et al., 2015).