GDNF and Parkinson disease: The therapeutic benefit of GDNF and NRTN has been demonstrated in phenotypic, toxin-induced [6-hydroxydopamine (6-OHDA) and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)] rodent and non-human primate models of PD (Bilang-Bleuel et al., 1997; Choi-Lundberg et al., 1997; Mandel et al., 1999; Kirik et al., 2000; Kordower et al., 2000; Eslamboli et al., 2003, 2005; Kordower et al., 2006; Gasmi et al., 2007a,b; Ramaswamy et al., 2007; Herzog et al., 2008, 2009; Su et al., 2009).