BDNF signaling is primarily mediated by binding to the high affinity tropomyosin-related kinase B receptor (TrkB), which can protect SNpc neurons in experimental models, and BDNF mRNA is reduced in the SNpc in PD (Hyman et al., 1991; Spina et al., 1992; Howells et al., 2000). The gene discussed is BDNF; the disease is Parkinson disease.