NTRK2 and Parkinson disease: Thus, dendritic and spine atrophy correlate with altered TrkB cell surface expression, indicating that dysregulated BDNF/TrkB signaling contributes to the pathophysiology of direct and indirect pathway striatal projection neurons in PD, and that long-term stimulation of DRD2 might re-establish TrkB phosphorylation to basal levels, rescuing spine morphology.