Fluoxetine prevents LPS-induced degeneration of nigral dopaminergic neurons by inhibiting microglia-mediated oxidative stress

Abstract

Lipopolysaccharide (LPS)-induced microglial activation causes degeneration of nigral dopaminergic (DA) neurons. Here, we examined whether fluoxetine prevents LPS-induced degeneration of DA in the rat substantia nigra (SN) in vivo. Seven days after LPS injection into the SN, immunostaining for tyrosine hydroxylase (TH) revealed a significant loss of nigral DA neurons. Parallel activation of microglia (visualized by OX-42 and ED1 immunohistochemistry), production of reactive oxygen species (ROS) (assessed by hydroethidine histochemistry), and degeneration of nigral DA neurons were also observed in the SN. Western blot analyses and double-label immunohistochemistry showed an increase in the expression of inducible nitric oxide synthase (iNOS) within activated microglia. LPS also induced translocation of p67(phox), the cytosolic component of NADPH oxidase, to the membrane of SN microglia, indicating activation of NADPH oxidase. The LPS-induced loss of nigral DA neurons was partially inhibited by fluoxetine, and the observed neuroprotective effects were associated with fluoxetine-mediated suppression of microglial NADPH oxidase activation and iNOS upregulation, and decreased ROS generation and oxidative stress. These results suggest that fluoxetine and analogs thereof may be beneficial for the treatment of neurodegenerative diseases, such as PD, that are associated with microglia-derived oxidative damage.