GDNF and Parkinson disease: Interestingly,TGF-β also behaves as a survival factor for midbrain dopaminergic neurons[42].Moving from the consistent neuroprotective and restoring activity in experimentalmodels of parkinsonism (see references in Introduction), GDNF has been evaluated inseveral clinical trials for its effect on Parkinson's disease.Intracerebroventricular injection of GDNF was inactive [43], whereas directintraputaminal infusion of GDNF produced beneficial effects in two phase-I clinicaltrials [44],[45],but was not successful in another double-blinded placebo controlled study [46].