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Photobiomodulation therapy is an innovative noninvasive modality for the treatment of a wide range of neurological and psychiatric disorders and can also improve healthy brain function. This protocol includes a step-by-step guide to performing brain photobiomodulation in mice by transcranial light delivery, which can be adapted for use in other laboratory rodents.
Transcranial photobiomodulation is a potential innovative noninvasive therapeutic approach for improving brain bioenergetics, brain function in a wide range of neurological and psychiatric disorders, and memory enhancement in age-related cognitive decline and neurodegenerative diseases. We describe a laboratory protocol for transcranial photobiomodulation therapy (PBMT) in mice. Aged BALB/c mice (18 months old) are treated with a 660 nm laser transcranially, once daily for 2 weeks. Laser transmittance data shows that approximately 1% of the incident red light on the scalp reaches a 1 mm depth from the cortical surface, penetrating the dorsal hippocampus. Treatment outcomes are assessed by two methods: a Barnes maze test, which is a hippocampus-dependent spatial learning and memory task evaluation, and measuring hippocampal ATP levels, which is used as a bioenergetics index. The results from the Barnes task show an enhancement of the spatial memory in laser-treated aged mice when compared with age-matched controls. Biochemical analysis after laser treatment indicates increased hippocampal ATP levels. We postulate that the enhancement of memory performance is potentially due to an improvement in hippocampal energy metabolism induced by the red laser treatment. The observations in mice could be extended to other animal models since this protocol could potentially be adapted to other species frequently used in translational neuroscience, such as rabbit, cat, dog, or monkey. Transcranial photobiomodulation is a safe and cost-effective modality which may be a promising therapeutic approach in age-related cognitive impairment.
PBMT, or low-level laser light therapy (LLLT), is a general term which refers to therapeutic methods based on the stimulation of biological tissues by light energy from lasers or light-emitting diodes (LEDs). Almost all PBMT treatments are applied with red to near-infrared (NIR) light at wavelengths from 600 to 1100 nm, an output power ranging from 1 to 500 mW, and a fluence ranging from <1 to >20 J/cm2 (see Chung et al.1).
Transcranial PBMT is a noninvasive light delivery method that is conducted by irradiation of the head using an external light source (laser or LEDs)2. For animal applications, this method includes contact or noncontact placement of the LED or laser probe on the animal's head. Depending on the therapeutic region of interest, a light probe can be placed either over the entire head (for covering all the brain areas) or over a specific portion of the head, such as the prefrontal, frontal, or parietal region. The partial transmission of red/NIR light through the scalp, skull, and dura mater can reach the cortical surface level and provide an amount of photon energy sufficient to produce therapeutic benefits. Subsequently, the delivered light fluence at the cortical level would be propagated into the gray and white brain matter until it reaches the deeper structures of the brain3.
Light in the spectral bands at the red to far-red region (600-680 nm) and early NIR region (800-870 nm) corresponds to the absorption spectrum of cytochrome c oxidase, the terminal enzyme of the mitochondrial respiratory chain4. It is hypothesized that PBMT in the red/NIR spectrum causes photodissociation of nitric oxide (NO) from cytochrome c oxidase, resulting in increases in mitochondrial electron transport and, ultimately, increased ATP generation5. With respect to neuronal applications, the potential neurostimulatory benefits of brain PBMT using transcranial irradiation methods have been reported in a variety of preclinical studies, including rodent models of traumatic brain injury (TBI)6, acute stroke7, Alzheimer's disease (AD)8, Parkinson's disease (PD)9, depression10, and aging11.
Brain aging is considered a neuropsychological condition that negatively affects some cognitive functions, such as learning and memory12. Mitochondria are the primary organelles responsible for ATP production and neuronal bioenergetics. Mitochondrial dysfunction is known to be associated with age-related deficits in brain areas that are linked to spatial navigation memory, such as the hippocampus13. Because cranial treatment with red/NIR light primarily acts by modulation of mitochondrial bioenergetics, sufficient delivered light dosage to the hippocampus can result in the improvement of spatial memory outcomes14.
The aim of the current protocol is to demonstrate the transcranial PBMT procedure in mice, using low levels of red light. The required laser light transmission measurements through the head tissues of aged mice are described. Additionally, Barnes maze, as a hippocampus-dependent spatial learning and memory task, and hippocampal ATP levels, as a bioenergetics index, are used for an evaluation of the treatment impact in animals.
All of the procedures were carried out in conformity with the Guide for the Care and Use of Laboratory Animals of the National Institutes of Health (NIH; Publication No. 85-23, revised 1985) and approved by the regional ethics committee of Tabriz University of Medical Sciences.
CAUTION: This protocol includes the application of Class 3B laser instruments and will require proper training and adherence to safety guidelines. Class 3B lasers can seriously damage the eyes and can heat the skin. Class 3B lasers are not considered a burn hazard. Eye protection goggles must be worn at all times when operating the laser device.
1. Laser light transmission experiments
NOTE: Used here were three 18-month-old male BALB/c mice obtained from the animal facility of Tabriz University of Medical Sciences. A 60 mW laser (660 nm) with a circular beam shape of 2.5 mm in diameter is used as the light source. The laser source produces a circularly polarized light with a Gaussian intensity profile and is operated in continuous wave mode. A commercial photodiode power meter with a 10 nW resolution, a square 1 cm2 photodiode active area, and a spectral response range from 400 to 1100 nm is used to measure the transmitted light power through the samples.
2. Photobiomodulation therapy (PBMT)
NOTE: Forty-five male BALB/c mice assigned to three groups of 15 mice each were used. The groups were composed of young-control mice (2 months old) that received sham-PBMT, aged-control mice (18 months old) that received sham-PBMT, and aged-PBMT mice (18 months old) that received PBMT. The sham-PBMT treatment consisted of treatment identical to the PBMT group but with the laser inactive. Mice were obtained from the animal facility of Tabriz University of Medical Sciences and were housed in the animal holding unit of the Neurosciences Research Center (NSRC) at 24-25 °C and 55% relative humidity, with a 12 h light and 12 h dark photoperiod. Food and water were provided ad libitum. All mice were acclimatized for at least 1 week prior to treatment.
3. Behavioral Tasks
4. Biochemical assessment
Statistical analyses
The statistical analysis of data obtained from the Barnes training sessions was analyzed by two-way ANOVA; the other behavioral tests and analysis of hippocampal ATP levels among groups were carried out by one-way ANOVA, followed by Tukey's post hoc test. All data are expressed as means ± the standard error of the mean (SEM), except for the laser transmission data, which are shown a...
We describe a protocol for conducting a transcranial PBMT procedure in mice. This protocol is specifically targeted to neuroscience laboratories that perform photobiomodulation research focused on rodents. However, this protocol can be adapted to other laboratory animals that are frequently used in the neuroscience field, such as rabbit, cat, dog, or monkey.
Currently, there is increased interest in investigating transcranial PBMT with red/NIR lasers and LEDs. In order to successfully carry ou...
P.C.'s salary was supported by the Harvard Psychiatry Department (Dupont-Warren Fellowship and Livingston Award), by the Brain and Behavior Research Foundation (NARSAD Young Investigator Award), and by the Photothera Inc. unrestricted grant. The drug donation came from TEVA. Travel reimbursement came from Pharmacia-Upjohn. P.C. has received consultation fees from Janssen Research and Development. P.C. has filed several patents related to the use of near-infrared light in psychiatry. PhotoMedex, Inc. supplied four devices for a clinical study. P.C. has received unrestricted funding from Litecure Inc. to conduct a study on transcranial photobiomodulation for the treatment of major depressive disorders and to conduct a study on healthy subjects. P.C. cofounded a company (Niraxx Light Therapeutics) focused on the development of new modalities of treatment based on near-infrared light; he is also a consultant for the same company. P.C. received funding from Cerebral Sciences to conduct a study on transcranial photobiomodulation for generalized anxiety disorder. The other authors have no conflicts of interest to disclose.
This work was supported by a grant from the Tabriz University of Medical Sciences (grant no. 61019) to S.S.-E. and a publication grant from LiteCure LLC, Newark, DE, USA to L.D.T. The authors would like to thank the Immunology Department and Education Development Center (EDC) of Tabriz University of Medical Sciences for their kind assistance.
Name | Company | Catalog Number | Comments |
Ketamine | Alfasan | #1608234-01 | |
Xylazine | Alfasan | #1608238-01 | |
Agarose | Sigma | #A4679 | |
Superglue | Quickstar | ||
Vibratome | Campden Instruments | #MA752-707 | |
Optical glass | Sail Brand | #7102 | |
Power meter | Thor labs | #PM100D | |
Photodiode detector | Thor labs | #S121C | |
Caliper | Pittsburgh | ||
GaAlAs laser | Thor Photomedicine | ||
Etho Vision | Noldus | ||
Centrifuge | Froilabo | #SW14R | |
Earmuffs | Blue Eagle | ||
Digital camera | Visionlite | #VCS2-E742H | |
Sterio amplifier | Sony | ||
Ethanol | Hamonteb | #665.128321 | |
Barnes maze | Costom-made | ||
ATP assay kit | Sigma | #MAK190 | |
Elisa reader | Awareness | #Stat Fax 2100 |
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