Low-level laser light therapy improves cognitive deficits and inhibits microglial activation after controlled cortical impact in mice

Abstract

Low-level laser light therapy (LLLT) exerts beneficial effects on motor and histopathological outcomes after experimental traumatic brain injury (TBI), and coherent near-infrared light has been reported to improve cognitive function in patients with chronic TBI. However, the effects of LLLT on cognitive recovery in experimental TBI are unknown. We hypothesized that LLLT administered after controlled cortical impact (CCI) would improve post-injury Morris water maze (MWM) performance. Low-level laser light (800 nm) was applied directly to the contused parenchyma or transcranially in mice beginning 60-80 min after CCI. Injured mice treated with 60 J/cm² (500 mW/cm²×2 min) either transcranially or via an open craniotomy had modestly improved latency to the hidden platform (p<0.05 for group), and probe trial performance (p<0.01) compared to non-treated controls. The beneficial effects of LLLT in open craniotomy mice were associated with reduced microgliosis at 48 h (21.8±2.3 versus 39.2±4.2 IbA-1+ cells/200×field, p<0.05). Little or no effect of LLLT on post-injury cognitive function was observed using the other doses, a 4-h administration time point and 7-day administration of 60 J/cm². No effect of LLLT (60 J/cm² open craniotomy) was observed on post-injury motor function (days 1-7), brain edema (24 h), nitrosative stress (24 h), or lesion volume (14 days). Although further dose optimization and mechanism studies are needed, the data suggest that LLLT might be a therapeutic option to improve cognitive recovery and limit inflammation after TBI.

Figures

FIG. 1.

Effect of low-level laser light therapy (LLLT) on wire grip test performance after controlled cortical impact. Motor function was assessed using the wire grip test on post-injury days 1, 3, 5, and 7. (A) Motor recovery did not differ between mice treated with 60 J/cm2 compared to injured control mice (p=0.35 for group; n=18–20/group). (B) Injured mice treated with 210 J/cm2 had no difference in their motor recovery compared to control mice (p=0.85 for group; n=7–8/group). Wire grip performance in all mice improved over the experimental period (p<0.0001 for time).

FIG. 2.

Effect of low-level laser light therapy (LLLT) on recovery of cognitive function after controlled cortical impact (CCI). Cognitive function was assessed using the Morris water maze. In the open craniotomy group, (A) mice treated with 60 J/cm2 performed significantly better than controls in the hidden platform (p=0.03 for group; n=22; upper panel) and probe trials (*p=0.004; lower panel). (B) Treatment with doses of 30 or 120 J/cm2 did not improve hidden platform trials (p>0.1 for group; n=7–10/group; upper panel), but mice treated with 120 J/cm2 had improved probe trial scores compared to controls (*p=0.02; lower panel). (C) Injured mice treated with 105 J/cm2 performed similarly to controls (p>0.05 for group effect on the hidden platform and probe trials; n=7/group). Mice treated with 210 J/cm2 had improved performance in the hidden platform (p=0.039 for group; n=8; upper panel), but not in the probe trials (p=0.95; lower panel). In mice treated with transcranial LLLT, (D) a single dose of 60 J/cm2 given 60–80 min post-injury improved hidden platform trial performance (p=0.018 for group; n=12–13/group; upper panel), and probe trial latency (*p=0.021 versus controls; lower panel). (E) Daily application of transcranial LLLT for 7 days after CCI had no benefit on the hidden platform trials (p=0.935 for group; n=10/group; upper panel); however, this regimen improved probe trial performance (*p<0.03 versus controls; lower panel). (F) Transcranial LLLT (60 J/cm2) administered at 4 h post-injury did not improve hidden platform (p=0.13 for group; n=9/group; upper panel) or probe trial performance (p=0.6 versus controls; lower panel). No significant differences among treatment groups were observed in the visible platform trials. All LLLT-treated and control (non-treated) mice showed progressive improvement in the hidden platform trials (p<0.0001 for time), indicating learning.

FIG. 3.

Effect of low-level laser light therapy (LLLT) on microglial activation after controlled cortical impact. Representative photomicrographs made at 48 h following injury show (A) normal resting microglia in the contralateral hemisphere, (B) robust microgliosis in the ipsilateral hemisphere of injured control (non-treated) mice, and (C) reduced microgliosis in the ipsilateral cortex following 60 J/cm2 laser treatment (magnification 200×). (D) Quantitative analysis of microgliosis assessed at 48 h showing significant reduction with 60 J/cm2 LLLT (*p=0.03 versus controls; scale bars=10 μm).

FIG. 4.

Effect of low-level laser light therapy (LLLT) on post-injury brain edema. Brain water content in injured hemispheres was significantly greater than that of uninjured hemispheres in all groups (*p<0.01); however, brain water content in injured hemispheres did not differ among treatment groups.

FIG. 5.

Effect of low-level laser light therapy (LLLT) on post-injury lesion volume. Brain tissue loss measured on day 14 post-injury did not differ between open craniotomy mice treated with 60 J/cm2 (n=16) versus controls (p=0.12; n=16).

FIG. 6.

Effect of low-level laser light therapy (LLLT) on protein nitrosylation in mouse brain at 24 h after controlled cortical impact (CCI). The total concentration of nitrosylated protein was significantly higher at 24 h post-CCI injury in LLLT-treated and non-treated controls compared to sham animals (*p<0.0001; n=8/group). Nitrotyrosine levels did not differ at 24 h after CCI between the LLLT (60 J/cm2) and non-treated control groups (p=0.65).