Transcranial low-level light therapy produces neuroprotection, neurogenesis and BDNF after TBI in mice

We have previously shown that transcranial low level light therapy (LLLT) can ameliorate brain damage in mice subjected to traumatic brain injury and improve neurological function. We used a 810-nm laser and delivered 18 J/cm2 at an irradiance 25 mW/cm2. LLLT was either delivered once at 4 hours after controlled cortical impact TBI, once a day for 3 days, or once a day for 14 days. One and 3 applications of LLLT had beneficial effects on the mice, with 3 being better than 1, but 14 applications had no beneficial effect. We now report immunofluorescence studies in mouse brain sections that offer some explanation for this intriguing finding. Mice were injected with BrdU for 1 week before sacrifice (a marker for proliferating cells) and antibodies to double cortin (DCX-1,a marker of migrating neurons), Tuj-1 ( a marker of neuroprogenitor cells), BDNF (brain derived neurotrophic factor) and synapsin-1 ( a marker for newly formed synaptic connections between existing neurons). We found increased BrdU incorporation indicating proliferating cells in the dentate gyrus of the hippocampus, the subventricular layer of the lateral ventricle, as well as the brain tissue surrounding the cortical lesion. Interestingly these cells were more abundant at 7 days than at 28 days post TBI. Co-labeling of BrdU with Neu-N was performed indicating that the proliferating cells were in fact neuronal in nature. Mice with 3 laser treatments had much more BrdU incorporation than mice with 14. Upregulation of BDNF was seen at 7 days, and increased expression of DCX-1 and Tuj-1 was seen at 28 days in the lesion region, indication that neuroprogenitor cells may have migrated there from sites of neurogenesis. Increased syapsin-1 was seen in the cortex at 28 days indicating that neural plasticity may be stimulated by LLLT. Taken together these data suggest that transcranial LLLT may have applications beyond TBI in areas such as neurodegenerative disease and psychiatric disorders.