GCG and Parkinson disease: One such drug, exendin-4 (EX-4), a glucagon-like peptide-1 (GLP-1) receptor agonist, currently in clinical use for type II diabetes, has demonstrated neuroprotective effects in several animal models of PD (Bertilsson et al., 2008; Harkavyi et al., 2008; Kim et al., 2009, 2017; Li et al., 2009; Cao et al., 2016; Chen et al., 2018; Yun et al., 2018).