Chronic Exposure To LED Lights Impairs Prefrontal Cortical Cognitive Functions In Rats

LEDs are widely used because of their high efficiency energy saving.Light can affect brain cognitive functions in a way independent of visual sensation.Previous studies have shown that chronic exposure to LED influences physiological functions in humans.However,it is not clear if it also influences the prefrontal cortex(PFC)-dependent cognitive functions.To address this question,we established an animal model,where SD rats were exposed to long-term LED illumination from 6:00 pm to 10:00 pm each day for one month(postnatal day 22-52)to simulate human illumination environment.We used elevated plus maze,novel-object recognition,social interaction,Morris water maze and sound-location association tasks to evaluate the cognitive functions of experimental rats,and employed immunohistochemistry and western-blotting to evaluate the myelination level of the medial prefrontal cortex(mPFC)of the rats.The results show that,chronic exposure to LED caused an increase in anxiety level,and impaired novel-object recognition ability,social interaction ability,spatial learning memory and sound-location association learning.The myelination level in the mPFC demonstrated a dramatic increase during the period of postnatal day 10 through and day 50,and chronic exposure to LED during such period induced a significant decrease in the myelination level and number of matured oligodendrocytes in the mPFC.The present results indicate that,chronic exposure to LED impairs the mPFC-dependent cognitive functions by down regulating the myelination of mPFC,suggesting that long-term use of LEDs is harmful for PFC cognitive functions.