GDNF and Parkinson disease: Therefore, both GDNF and NRTN have been extensively studied in various toxin-based models of PD in rodents and primates and showed remarkable neuroprotective and neurorestorative properties (Hoffer et al. 1994; Bowenkamp et al. 1995; Beck et al. 1995; Gash et al. 1996; Horger et al. 1998; Kirik et al. 2000; Kordower et al. 2000; Oiwa et al. 2002; Runeberg-Roos et al. 2016).