Comparison of therapeutic effects between pulsed and continuous wave 810-nm wavelength laser irradiation for traumatic brain injury in mice

Abstract

Background and objective: Transcranial low-level laser therapy (LLLT) using near-infrared light can efficiently penetrate through the scalp and skull and could allow non-invasive treatment for traumatic brain injury (TBI). In the present study, we compared the therapeutic effect using 810-nm wavelength laser light in continuous and pulsed wave modes in a mouse model of TBI.

Study design/materials and methods: TBI was induced by a controlled cortical-impact device and 4-hours post-TBI 1-group received a sham treatment and 3-groups received a single exposure to transcranial LLLT, either continuous wave or pulsed at 10-Hz or 100-Hz with a 50% duty cycle. An 810-nm Ga-Al-As diode laser delivered a spot with diameter of 1-cm onto the injured head with a power density of 50-mW/cm(2) for 12-minutes giving a fluence of 36-J/cm(2). Neurological severity score (NSS) and body weight were measured up to 4 weeks. Mice were sacrificed at 2, 15 and 28 days post-TBI and the lesion size was histologically analyzed. The quantity of ATP production in the brain tissue was determined immediately after laser irradiation. We examined the role of LLLT on the psychological state of the mice at 1 day and 4 weeks after TBI using tail suspension test and forced swim test.

Results: The 810-nm laser pulsed at 10-Hz was the most effective judged by improvement in NSS and body weight although the other laser regimens were also effective. The brain lesion volume of mice treated with 10-Hz pulsed-laser irradiation was significantly lower than control group at 15-days and 4-weeks post-TBI. Moreover, we found an antidepressant effect of LLLT at 4-weeks as shown by forced swim and tail suspension tests.

Conclusion: The therapeutic effect of LLLT for TBI with an 810-nm laser was more effective at 10-Hz pulse frequency than at CW and 100-Hz. This finding may provide a new insight into biological mechanisms of LLLT.

Figure 1. Laser transmission through scalp and skull.

Plot of measured incident laser power against measured transmitted laser power in CW mode through mouse scalp and scalp and skull combined. Values are expressed as mean ± S.D; n = 3.

Figure 2. NSS scores after laser treatment.

(A) Time course of neurological severity score (NSS) of mice with TBI receiving either control (no laser-treatment), or 810-nm laser (36 J/cm² delivered at 50 mW/cm² with a spot size of 0.78 cm²) in either CW, PW 10 Hz or PW 100 Hz modes. Results are expressed as mean ± S.E.M (n = 10). *** P<0.001 vs. the other conditions. (B) Mean areas under the NSS-time curves in the two-dimensional coordinate system over the 28-day study for the 4 groups of mice. Results are means ± SD (n = 10).

Figure 3. Body weight as a measure of health status.

Variation of total body weight in healthy (sham control; n = 3), traumatic brain injury (TBI) and 3 groups of 810-nm laser-treated mice (n = 10).

Figure 4. Forced swim test for depression.

Immobility duration in forced swim test (FST) at (A) 1 day and (B) 28 days after brain injury and laser irradiation. Values are in mean ± S.E.M. (n = 10). ‡ P<0.05 vs. values at 1 day after TBI. * P<0.05 between the groups.

Figure 5. Tail suspension test for depression and anxiety.

Tail suspension test (TST) showing immobility periods out of 360 sec total test duration carried out at (A) 1 day; and (B) 28 days after TBI and laser irradiation. Values are in mean ± S.E.M. (n = 10). * P<0.05.

Figure 6. ATP content in brain.

Cortical ATP content in mice brain tissue of left side (traumatic injury) immediately after laser treatment. Values are in mean ± S.E.M. (n = 5).

Figure 7. Histology of brain slices.

Histological images of cross-sections of brains from control non-laser-treated and laser-treated TBI mice removed at day 28.

Figure 8. Area of brain lesions.

Results of quantitative analysis of the area of cavitary cortical lesions in brain tissue on the basis of the histological images. Values are means ± S.E.M. (n = 9). * P<0.05.