Photobiomodulation enhances nigral dopaminergic cell survival in a chronic MPTP mouse model of Parkinson's disease

We have shown previously that photobiomodulation or near-infrared light (NIr) treatment protects dopaminergic cells of the substantia nigra pars compacta (SNc) in an acute MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) model of Parkinson's disease (PD). In this study, we tested the protective and rescue action of NIr treatment in a chronic MPTP model, developed to resemble more closely the slow progressive degeneration in PD patients. We examined three regions of dopaminergic cells, the SNc, periaqueductal grey matter (PaG) and zona incerta-hypothalamus (ZI-Hyp). BALB/c mice had MPTP or saline injections over five weeks, followed by a three-week survival. NIr treatment was applied either at the same time as (simultaneous series) or after (post-treatment series) the MPTP insult. There were four groups within each series; Saline, Saline-NIr, MPTP and MPTP-NIr. Brains were processed for tyrosine hydroxylase (TH) immunochemistry and cell number was analysed using the optical fractionator method. In the SNc, there was a significant reduction (∼45%) in TH+ cell number in the MPTP groups compared to the saline controls of both series. In the MPTP-NIr groups of both series, TH+ cell number was significantly higher (∼25%) than in the MPTP groups, but lower than in the saline controls (∼20%). By contrast in the PaG and ZI-Hyp, there were no significant differences in TH+ cell number between the MPTP an MPTP-NIr groups of either series. In summary, exposure to NIr either at the same time or well after chronic MPTP insult saved many SNc dopaminergic cells from degeneration.