Chronic Exposure to Dim Light at Night or Irregular Lighting Conditions Impact Circadian Behavior, Motor Coordination, and Neuronal Morphology

Abstract

Mistimed exposure to light has been demonstrated to negatively affect multiple aspects of physiology and behavior. Here we analyzed the effects of chronic exposure to abnormal lighting conditions in mice. We exposed mice for 1 year to either: a standard light/dark cycle, a “light-pollution” condition in which low levels of light were present in the dark phase of the circadian cycle (dim light at night, DLAN), or altered light cycles in which the length of the weekday and weekend light phase differed by 6 h (“social jetlag”). Mice exhibited several circadian activity phenotypes, as well as changes in motor function, associated particularly with the DLAN condition. Our data suggest that these phenotypes might be due to changes outside the core clock. Dendritic spine changes in other brain regions raise the possibility that these phenotypes are mediated by changes in neuronal coordination outside of the clock. Given the prevalence of artificial light exposure in the modern world, further work is required to establish whether these negative effects are observed in humans as well.

Outdoor Nighttime Light Exposure (Light Pollution) is Associated with Alzheimer’s Disease

“…Amish communities have a lower prevalence of cognitive impairment in individuals of advanced age compared to the general population (Johnson et al 1997; Holder and Warren 1998; Pericak-Vance et al 1996). Numerous factors other than light exposure may contribute to this phenomenon (e.g., emphasis on family / community, traditional farming, genetics), but that being said, exposure of Drosophila to dim light during the dark period promotes neurodegeneration (Kim et al 2018), and data from mice demonstrate that dim light during the dark period alters neuronal dendrites in AD-relevant brain regions (cortex, hippocampus) (Delorme et al 2022), and long-term exposure to outdoor light at night is associated with increased risk of cognitive impairment in humans (Chen et al 2022), and there is a positive correlation between light pollution and Parkinson’s disease (another neurodegenerative disease) (Romeo et al 2013). Additional studies carefully evaluating indoor and outdoor light exposure and mechanistic evaluations are needed to fully understand the impact of nighttime light exposure and light pollution on AD.…”

“…Incidence and prevalence of AD have increased in recent decades which parallels the increase in light pollution. Evidence suggests that exposure to light at night may promote neurodegeneration, neuroinflammation, dementia, and AD (Kim et al 2018; Delorme et al 2022; Walker et al 2020; Chen et al 2022; Mazzoleni et al 2023; Romeo et al 2013), but this possibility has not been carefully examined.…”

Artificial Dim Light at Night during Pregnancy Can Affect Hormonal and Metabolic Rhythms in Rat Offspring

“…Although we did not measure the melatonin levels in pregnant female rats in this study to avoid an additional stress stimulus, our previous studies convincingly showed that the night-time illuminance applied in this experiment suppressed plasma melatonin rhythm in adult male rats [ 35 , 37 ]. In previous studies, higher levels of ALAN were applied to explore the effect of ALAN, from 5 lx [ 13 , 15 ] to 20 lx [ 38 ]. Autonomous rhythmic melatonin biosynthesis starts in rats at postnatal day 5 in the pineal gland [ 36 ], and therefore, the melatonin plasma levels in 3-day-old offspring reflect maternal melatonin.…”

Shift work-like patterns effect on female and male mouse behavior

“…This daily rhythm stability maintained over the weeks of repeated shift-paradigm could explain the mild effect of shift work-like patterns on mouse behaviors. Several studies have shown that the negative impact of circadian disruption depends upon the degree to which an animal is able to entrain to the disruptive conditions and that if mice can make some degree of adjustment to the shift-work conditions, the deleterious effects on health may be mitigated( Delorme et al, 2022 ; Inokawa et al, 2020 ). However, the correlation analysis we present here suggests that, at the level of the individual animal, certain behaviors may still be impacted by previous periods of circadian disruption.…”