Red-light radiation: does it enhance memory by increasing hippocampal LRP-1 and TRPA-1 genes expression?

Purpose: Despite the extensive efforts to treat the leading cause of neurodegenerative diseases (ND), a little progress has been reported. Red light might affect ND through many specific mechanisms. The purpose of this investigation is to explore the effect of red light on the expression of low-density lipoprotein receptor-1 (LRP-1) and transient receptor potential ankyrin-1 (TRPA-1) gene in the hippocampus, and the serum melatonin level (SML) of the lipopolysaccharide (LPS)-induced neuro-inflammated rats.

Materials and methods: Red-light therapy was implemented using a wavelength 630 nm under different light conditions and the passive avoidance (PA) and Y-Maze tests were employed to assess memory performance. To evaluate the LRP-1 and TRPA-1 genes expression, quantitive real-time polymerase chain reaction was performed. To measure the SML, ELISA was performed before and after the red-light radiation.

Results: LPS caused memory impairment in both behavioral tests. Red-light therapy improved PA memory in all light conditions (p < .001). However, in Y-maze, only the red-light radiation during light and dark cycles, improved memory (p < .01 and p < .001, respectively). In addition, red-light radiation caused significant increase in SML (p < .05). The LRP-1 and TRPA-1 genes expression increased significantly during the dark phase in the red light radiated group compared to non-radiated group (p < .001).

Conclusions: Taken together, the results suggest that red-light therapy can reduce the complications of memory impairment in rats. This study has found that red-light therapy demonstrates higher effect during the period of dark phase compared to light phase. No doubt, further experimental studies would help us to establish a greater degree of accuracy on this matter.