BDNF and Parkinson disease: However, PD disrupts the processing of pro-BDNF to mature BDNF, impairing the BDNF–TrkB signaling pathway, which is crucial for dendritic growth, spine maturation, and synaptic plasticity through dopamine D1 receptor-dependent cyclic AMP (cAMP) signaling in the NS (Palasz et al., 2020).