Fig. 2.

Intranigral grafting is attractive as a way to achieve more complete circuitry repair, more refined functional regulation of the grafted neurons, and more widespread reinnervation of the DA-deficient forebrain areas. The use of this approach in the human brain, however, is a challenge due to the 10-fold greater length of the human DA system (A), compared to the one in the rat brain (B). This may require a combined therapeutic approach where growth promoting factors are used to increase the growth capacity of the grafted mDA neurons.