GDNF and Cognitive impairment: GDNF can increase total DAT expression in the striatum of a 6-OHDA-treated rat model of PD26,27. Our previous study found that decreased GDNF in the PFC triggered deficits in dopaminergic synaptic transmission, such as the degeneration of dopaminergic synaptic function, which may contribute to cognitive impairment in patients with PD28.