Effects of transcranial near-infrared photobiomodulation on hippocampal synapse plasticity in a rat model of alzheimer`s disease

Abstract

Alzheimer's disease (AD) is one of the most common causes of dementia in old age, which is due to extracellular deposition of amyloid beta (β-Amyloid) plaques and intracellular accumulation of neurofibrillary tangles (NFTs), resulting in a decrease in brain volume and the number of synapses. Currently, there is no definitive treatment for AD and the drugs used are not effective due to side effects, various drug interactions, and the patient's lack of acceptance. Considering that light therapy (PBM) can improve cognitive and memory functions, in this study, the effect of transcranial near-infrared laser radiation on spatial memory and electrical activity of hippocampal neurons in an animal AD model was investigated. Materials and methods: In this study, 48 male Wistar rats (weighing approximately 250-300 grams) were used. The animals were randomly divided into 6 groups including control, surgical sham, Alzheimer's model (AD), Alzheimer's model treated with 8 J laser, Alzheimer's model treated with 16 J laser, and Alzheimer's model treated with 32 J laser. To induce AD model, amyloid beta (Aβ1-42) was injected into the lateral cerebral ventricles. In the treatment groups, the animals were exposed to 810 nm transcranial laser radiation with energies of 8, 16, and 32 joules daily for 14 consecutive days. Learning and spatial memory of the animals were evaluated by Barnes maze test, then by placing the recording electrode in the CA1 region and the stimulation electrode in the right hippocampus, the electrical activity of the neurons in the CA1 region was recorded by performing the high frequency stimulation protocol. Results: 8 J laser irradiation for 14 days in AD rats significantly improved the spatial memory in the Barnes test compared to the AD group. Also, the results of electrophysiological recording showed that compared to before high frequency stimulation, the AD, 16 and 32 J laser groups did not show a significant increase in fEPSP slope. While this change was significant for the control, sham and 8J groups. In addition, compared to the AD group, fEPSP slopes were significantly increased by inducing LTP in both the control and 8J groups. However, no significant increase in fEPSP slope was observed in the 16 J and 32 J groups compared to the AD group.