TH and type 2 diabetes mellitus: However, very interestingly, double immunofluorescence labeling with TH and α-synuclein antibodies showed that the majority of TH positive neurons (up to 90%) in the substantia nigra of the diabetic monkeys contained significantly increased levels of α-synuclein (Figures 9c–f, arrows, and Supplementary Video S1), compared to the ones in the normal monkeys (Figures 9g–j and Supplementary Video S2), implying that T2DM induces accumulation of α-synuclein in dopaminergic neurons, as an early feature of pathology (Li et al., 2008).