SNCA and major depressive disorder: Another study compared the non-motor symptoms of three PD models (Campos et al., 2013): 6-OHDA (8 or 6 μg, stereotactic injection of bilateral substantia nigra pars compacta), paraquat (micro-osmotic pump implanted in the subscapular area at the rate of 0.7 mg/day for 28 days) and α-synuclein overexpression transgenic model, and found that 6-OHDA and paraquat-induced depression-like behavioral changes in model animals.