GCG and diabetes mellitus: Recent studies have emerged supporting the notion that glucagon-like peptide-1 (GLP-1), as well as long-acting GLP-1 receptor (GLP-1R) agonists approved for the treatment of type 2 diabetic mellitus (T2DM), may also be used as new non-DA replacement anti-Parkinsonian drugs by mitigating DA neuron degeneration [15,16].