Effect of Photobiomodulation in Rescuing Lipopolysaccharide-Induced Dopaminergic Cell Loss in the Male Sprague-Dawley Rat.

Photobiomodulation (PBM) provides neuroprotection against dopaminergic cell death and associated motor deficits in rodent and primate models of Parkinson's disease (PD). However, it has not yet been tested in the lipopolysaccharide (LPS) model of PD, which leads to dopaminergic cell death through microglia-evoked neuroinflammation. We investigated whether transcranial PBM could protect against dopaminergic cell death within the substantia nigra in male Sprague-Dawley rats following supranigral LPS injection. PBM fully protected rats from 10 µg LPS which would have otherwise caused 15% cell loss, but there was no significant neuroprotection at a 20 µg dose that led to a 50% lesion. Cell loss at this dose varied according to the precise site of injection and correlated with increased local numbers of highly inflammatory amoeboid microglia. Twenty microgram LPS caused motor deficits in the cylinder, adjusted stepping and rotarod tests that correlated with dopaminergic cell loss. While PBM caused no significant improvement at the group level, motor performance on all three tests no longer correlated with the lesion size caused by 20 µg LPS in PBM-treated rats, suggesting extranigral motor improvements in some animals. These results provide support for PBM as a successful neuroprotective therapy against the inflammatory component of early PD, provided inflammation has not reached a devastating level, as well as potential benefits in other motor circuitries.