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It is a well-known fact that following a proper routine light/dark or diurnal rhythm controls almost all biological processes. With the introduction of modern lighting and artificial illumination systems, continuous exposure to light at night may lead to the disruption of diurnal rhythm. However, the effect of light during the night on brain anatomy, physiology, and human body functions is less explored and poorly understood. In this study, we have evaluated the effect of exposure to dim light (5 lux) at night (dLAN) on Swiss Albino mice over a duration of three consecutive weeks. Results have revealed that exposure to dLAN led to an impairment of cognitive and non-cognitive behaviour, oxidative stress–mediated elevation of lipid peroxidation, and reduction of superoxide dismutase and catalase activity. It also led to the downregulation of hippocampal proteins (BDNF, Synapsin II and DCX) at both protein and mRNA level. Additionally, there was downregulation of CREB and SIRT1 mRNAs and neurodegeneration-associated miRNA21a-5p and miRNA34a-5p. The pyramidal and cortical neurons started showing pyknotic and chromatolysis characteristics. However, a dose of curcumin administered to the mice positively modulated these parameters in our experimental animals. We proposed the modulatory role of curcumin in addressing the deleterious effects of dLAN.

Age-related neurodegenerative diseases and vascular dementia are major challenges to the modern health care system. Most neurodegenerative diseases are associated with impaired spatial working memory and anxiety-like behavior. Thus, it is important to understand the underlying cellular mechanisms of neurodegenerative diseases in different regions of the brain to develop an effective therapeutic approach. In our previous research paper, we have reported the ameliorative effect of curcumin in Cd-induced hippocampal neurodegeneration. However, recently many researchers had reported the important role of the prefrontal cortex in higher cognitive functions. Therefore, to look into the cellular mechanism of curcumin protection against Cd-induced prefrontal cortex neurotoxicity, we investigated spatial working memory, anxiety-like behavior and analyzed prefrontal cortex inflammatory markers (IL-6, IL-10, and TNFα), antioxidant enzymes (SOD, GSH, and CAT), and pro-oxidant MDA level. Further, we conducted histological studies of the prefrontal cortex in Swiss albino mice exposed to cadmium (2.5 mg/kg). We observed that curcumin treatment improved the spatial working memory and anxiety-like behavior of mice through reduction of prefrontal cortex neuroinflammation and oxidative stress as well as increasing the number of viable prefrontal cortex neuronal cells. Our result suggests that environmental heavy metal cadmium can induce behavioral impairment in mice through prefrontal cortex cellular inflammation and oxidative stress. We found that curcumin has a potential therapeutic property to mitigate these behavioral and biochemical impairments induced by cadmium.

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In the modern research field, laboratory animals are constantly kept under artificial lighting conditions. However, recent studies have shown the effect of artificial light on animal behavior and metabolism. In the present study on mice, following three weeks of housing in dim light at night (dLAN; 5lux) and complete darkness (DD; 0lux), we monitored the effect on body weight, daily food intake, anxiety-like behavior by employing the open field test, and expression of the period (PER1) gene. We also studied the effect of oral administration of different concentrations of curcumin (50, 100, and 150 mg/kg) for three weeks in the same mice and monitored these parameters. The exposure to dLAN had significantly increased the anxiety-like behavior and body weight possibly through the altered metabolism in mice, whereas exposure to DD caused increased anxiety but no significant difference in weight gain. Moreover, the expression of the PER1 gene involved in sleep was also found to be decreased in the aberrant light conditions (dLAN and DD). Although the treatment of curcumin had no effect on body weight, it ameliorated the anxiety-like behavior possibly by modulating the expression of the PER1 gene. Thus, alteration in the light/dark cycle had a negative effect on laboratory animals on the body weight and emotions of animals. The present study identifies the risk factors associated with artificial lighting systems on the behavior of laboratory animals and the ameliorative effects of curcumin, with a focus on anxiety-like behavior.