MC4R and obesity disorder: Neural circuits related to obesity and mental disorders, such as melanocortin 4 receptor neurons, play a role in regulating mentally-associated weight gain by receiving GABAergic (GABA: gamma-aminobutyric acid) projections from hypothalamic agouti-related peptide (AgRP) neurons onto α 5-containing GABAA (gamma-aminobutyric acid type A) receptors and serotonergic afferents onto 5-Hydroxytryptamine type 3 receptors.