Administering a track of GDNF from the fetal graft in the SNpc to striatum facilitated outgrowth and improved rotational behavior in lesioned rats.112 This strategy was adapted in a NHP model of PD that utilized viral-vector-mediated overexpresion of GDNF in the striatum, enabling outgrowth from a fetal graft in the SNpc toward the striatum. Here, GDNF is linked to Parkinson disease.