Background: Misfolded alpha-synuclein (alpha-Syn) aggregates participate in the pathogenesis of synucleinopathies, such as Parkinson's disease. Whereas much is known about how the various domains within full-length alpha-Syn (FL-alpha-Syn) contribute to the formation of alpha-Syn aggregates and therefore to their neurotoxicity, little is known about whether the individual peptides that can be generated from alpha-syn, possibly as intermediate metabolites during degradation of misfolded alpha-Syn aggregates, are neurotoxic themselves. Methods: A series of synthesized alpha-Syn peptides, corresponding to the locus in FL-alpha-Syn containing alanine 30, substitution of which with a proline causes a familial form of Parkinson's disease, were examined for their capacity of inducing release of microglial superoxide. The neurotoxicity of these peptides was measured according to their influence on the ability of neuroglial cultures deficient in gp91(phox), the catalytic unit of NADPH oxidase (Nox2), or wild-type cultures to take up 3H-labeled dopamine and on the number of tyrosine hydroxylase-staining-positive neurons. Western blots and confocal images were utilized to analyze membrane translocation of p47(phox) and p67(phox), phosphorylation of p47phox and Erk1/2 kinase, and binding of alpha-Syn peptides to gp91(phox). Activation of brain microglia in mice injected with alpha-Syn peptides was demonstrated by immunostaining for major histocompatibility complex (MHC)-II along with qPCR for Ib alpha-1 and MHC-II. Results: We report alpha-Syn (29-40) as a specific peptide capable of activating microglial Nox2 to produce superoxide and cause dopaminergic neuronal damage. Administered to mice, this peptide also activated brain microglia to increase expression of MHC-II and Ib alpha-1 and stimulated oxidation reaction. Exploring the underlying mechanisms showed that alpha-Syn (29-40) peptide triggered Nox2 to generate extracellular superoxide and its metabolite H2O2 by binding to the catalytic unit gp91(phox) of Nox2; diffusing into cytosol, H2O2 activated Erk1/2 kinase to phosphorylate p47(phox) and p67(phox) and further activated Nox2, establishing a positive feedback loop to amplify the Nox2-mediated response. Conclusions: Collectively, our study suggests novel information regarding how alpha-Syn causes neuronal injury, possibly including mechanisms involving abnormal metabolites of alpha -Syn aggregates.