HERPUD1 and major depressive disorder: Melanostatin (MIF-1) is a naturally occurring neuropeptide acting as a positive allosteric modulator (PAM) of dopamine D<sub>2</sub> receptors (D<sub>2</sub>R), underscoring its potential for therapeutic use in central nervous system disorders associated with dopaminergic dysregulation, including depression, drug addiction, restless legs syndrome, tardive dyskinesia, and Parkinson's disease.