Low-level laser therapy for traumatic brain injury in mice increases brain derived neurotrophic factor (BDNF) and synaptogenesis

Abstract

Transcranial low-level laser (light) therapy (LLLT) is a new non-invasive approach to treating a range of brain disorders including traumatic brain injury (TBI). We (and others) have shown that applying near-infrared light to the head of animals that have suffered TBI produces improvement in neurological functioning, lessens the size of the brain lesion, reduces neuroinflammation, and stimulates the formation of new neurons. In the present study we used a controlled cortical impact TBI in mice and treated the mice either once (4 h post-TBI, 1-laser), or three daily applications (3-laser) with 810 nm CW laser 36 J/cm(2) at 50 mW/cm(2). Similar to previous studies, the neurological severity score improved in laser-treated mice compared to untreated TBI mice at day 14 and continued to further improve at days 21 and 28 with 3-laser being better than 1-laser. Mice were sacrificed at days 7 and 28 and brains removed for immunofluorescence analysis. Brain-derived neurotrophic factor (BDNF) was significantly upregulated by laser treatment in the dentate gyrus of the hippocampus (DG) and the subventricular zone (SVZ) but not in the perilesional cortex (lesion) at day 7 but not at day 28. Synapsin-1 (a marker for synaptogenesis, the formation of new connections between existing neurons) was significantly upregulated in lesion and SVZ but not DG, at 28 days but not 7 days. The data suggest that the benefit of LLLT to the brain is partly mediated by stimulation of BDNF production, which may in turn encourage synaptogenesis. Moreover the pleiotropic benefits of BDNF in the brain suggest LLLT may have wider applications to neurodegenerative and psychiatric disorders. Neurological Severity Score (NSS) for TBI mice.

Keywords: BDNF; Synapsin-1; neurogenesis; synaptogenesis; transcranial low level light therapy; traumatic brain injury.

© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Figures

Figure 1

NNS scores of the mice. Mean (n = 8–14) NSS scores measured over 7 and 28 days of mice in 8 groups consisting of sham TBI mice, sham control mice, 810 nm laser treated TBI mice (18 J/cm2 delivered at 25 mW/cm2). Mice were either given 1 laser Tx or 1 sham Tx at 4 hours post TBI or 3 daily laser Tx or 3 sham Tx; *p < 0.05; **P < 0.01; ***p < 0.001.

Figure 2

Protein expression of BDNF in the Dentate Gyrus area of brain sections (Mean n = 4). Immunofluorescence showing protein expression of BDNF at 400 × magnification in brain tissue of mice sacrificed at 7 or 28 days post-TBI. DAPI was used to stain the nuclei. (A) Sham- control mouse euthanized at day 7 (B) Sham-control mouse euthanized at day 28 (C) TBI-sham laser mice euthanized at day 7. (D) TBI-sham laser mice euthanized at day 28. (E) TBI mouse treated with 1 laser treatment euthanized at day 7. (F) TBI mouse treated with 1 laser treatment euthanized at day 28. (G) TBI mouse treated with 3 laser treatment euthanized at day 7 (H) TBI mouse treated with 3 laser treatment euthanized at day 28 (I) Mean fluorescent intensity (MFI) of BDNF immunostaining in brain sections measured in arbitrary units (AU) (using NIH Image J software). Data is shown as mean ± SEM from six measurements per mouse. **P < 0.01

Figure 3

Protein expression of BDNF in the SVZ area of brain sections (Mean n = 4). Immunofluorescence showing protein expression of BDNF at 400× magnification in brain tissue of mice sacrificed at 7 or 28 days post-TBI. DAPI was used to stain the nuclei. (A) Sham- control mouse euthanized at day 7 (B) Sham- control mouse euthanized at day 28 (C) TBI-sham laser mice euthanized at day 7. (D) TBI-sham laser mice euthanized at day 28. (E) TBI mouse treated with 1 laser treatment euthanized at day 7. (F) TBI mouse treated with 1 laser treatment euthanized at day 28. (G) TBI mouse treated with 3 laser treatment euthanized at day 7 (H) TBI mouse treated with 3 laser treatment euthanized at day 28 (I) Mean fluorescent intensity (MFI) of BDNF immunostaining in brain sections measured in arbitrary units (AU) (using NIH Image J software). Data is shown as mean ± SEM from six measurements per mouse; *p < 0.05; **P < 0.01; ***p < 0.001.

Figure 4

Protein expression of synapsin-1 in the SVZ area of brain sections (Mean n = 4). Immunofluorescence showing protein expression of synapsin-1 at 400× magnification in brain tissue of mice sacrificed at 7 or 28 days post-TBI. DAPI was used to stain the nuclei. (A) Sham- control mouse euthanized at day 7 (B) Sham- control mouse euthanized at day 28 (C) TBI-sham laser mice euthanized at day 7. (D) TBI-sham laser mice euthanized at day 28. (E) TBI mouse treated with 1 laser treatment euthanized at day 7. (F) TBI mouse treated with 1 laser treatment euthanized at day 28. (G) TBI mouse treated with 3 laser treatment euthanized at day 7 (H) TBI mouse treated with 3 laser treatment euthanized at day 28 (I) Mean fluorescent intensity (MFI) of synapsin-1 immunostaining in brain sections measured in arbitrary units (AU) (using NIH Image J software). Data is shown as mean ± SEM from six measurements per mouse; *p < 0.05.

Figure 5

Protein expression of synapsin-1 in the lesion area of brain sections (Mean n = 4). Immunofluorescence showing protein expression of synapsin-1 at 400× magnification in brain tissue of mice sacrificed at 7 or 28 days post-TBI. DAPI was used to stain the nuclei. (A) Sham- control mouse euthanized at day 7 (B) Sham- control mouse euthanized at day 28 (C) TBI-sham laser mice euthanized at day 7. (D) TBI-sham laser mice euthanized at day 28. (E) TBI mouse treated with 1 laser treatment euthanized at day 7. (F) TBI mouse treated with 1 laser treatment euthanized at day 28. (G) TBI mouse treated with 3 laser treatment euthanized at day 7 (H) TBI mouse treated with 3 laser treatment euthanized at day 28 (I) Mean fluorescent intensity (MFI) of synapsin-1 immunostaining in brain sections measured in arbitrary units (AU) (using NIH Image J software). Data is shown as mean ± SEM from six measurements per mouse. ** P < 0.01.