BDNF and Parkinson disease: BDNF is a neurotrophic factor for dopaminergicneurons of the SN, the region affected by PD (30).Reduced expression of BDNF within the SN has beenshown to cause the loss of dopaminergic neurons in PD.Indeed, postmortem studies of PD patients showed thata reduction in BDNF accompanied PD and BDNF wasrequired to preserve neurons of the SN pars compacta (34).In this study, we assessed BDNF gene expression by real-time PCR.