Exposure to prolonged unpredictable light impairs spatial memory via induction of oxidative stress and tumor necrosis factor-alpha in rats

Abstract

Abstract Objectives The human body physiology rapidly changes and adapt to several environmental stimuli, including light. Abnormal artificial light exposures have been shown to affect sleep cycle, cognition, and mood. Although studies have reported inconsistent effects of short-term or constant long-term light exposures, human exposures to artificial lights occur at varying, unpredictable times and duration daily. Here, we studied the effects of long-term unpredictable light exposure on learning, memory, oxidative status, and associated cytokines in rats. Methods Artificial lighting was provided using an array of white light-emitting diodes coupled to a microcontroller that switches them on or off at unpredictable times and duration (light intensity = 200 ± 20 lx). Within the last eight days of 40 days exposure, animals were subjected to open field test, Morris water maze, and novel object recognition behavioral paradigms. Brain levels of malondialdehyde (MDA), superoxide dismutase (SOD), catalase, reduced glutathione (GSH), glutathione S-transferase (GST), tumor necrosis factor-alpha (TNF-α), and vascular endothelial growth factor (VEGF) were assayed. Results Exposed rats showed impaired spatial learning and memory (p<0.05), but no changes in object recognition memory or locomotor activity. Oxidative stress analyses also revealed significant changes in the concentrations of MDA, SOD, catalase, and GSH levels (p<0.05), not GST. Similarly, there was an increased TNF-α expression (p<0.05), not VEGF. Conclusions We conclude that oxidative stress is involved in memory impairment in rats exposed to prolonged unpredictable lights, which again suggests the detrimental effects of extended light exposure on the nervous system.