Nighttime Light Hurts Mammalian Physiology: What Diurnal Rodent Models Are Telling Us

Abstract

Natural sunlight permits organisms to synchronize their physiology to the external world. However, in current times, natural sunlight has been replaced by artificial light in both day and nighttime. While in the daytime, indoor artificial light is of lower intensity than natural sunlight, leading to a weak entrainment signal for our internal biological clock, at night the exposure to artificial light perturbs the body clock and sleep. Although electric light at night allows us “to live in darkness”, our current lifestyle facilitates nighttime exposure to light by the use, or abuse, of electronic devices (e.g., smartphones). The chronic exposure to light at nighttime has been correlated to mood alterations, metabolic dysfunctions, and poor cognition. To decipher the brain mechanisms underlying these alterations, fundamental research has been conducted using animal models, principally of nocturnal nature (e.g., mice). Nevertheless, because of the diurnal nature of human physiology, it is also important to find and propose diurnal animal models for the study of the light effects in circadian biology. The present review provides an overview of the effects of light at nighttime on physiology and behavior in diurnal mammals, including humans. Knowing how the brain reacts to artificial light exposure, using diurnal rodent models, is fundamental for the development of new strategies in human health based in circadian biology.

Circadian Rhythms Disrupted by Light at Night and Mistimed Food Intake Alter Hormonal Rhythms and Metabolism

“…Thus, the mechanisms mediating the effects of ALAN on sleep and metabolism may not be coupled or may differ by species. A recent review of the “light-at-night” literature in the context of mammals, provides evidence to suggest more nuanced effects on sleep in diurnal versus nocturnal creatures [ 212 ]. In sum, this body of work supports the notion that circadian disruptors can differentially affect individual circadian processes, and that the interaction of individually affected pathways and processes may result in compounding and complex effects that need to be further examined.…”

The influence of climate and the presence of predators on the daily activity pattern of collared peccaries (Dicotyles tajacu, Cetartiodactyla)

“…An effective form of adaptation to minimize predation risk is the modification of the daily activity pattern, that is, prey change their daily activity pattern in a way that it does not overlap with that of predators (Gordigiani et al., 2022; Morais et al., 2019; Mori et al., 2020). The collared peccaries are often recorded foraging during the day (Galetti et al., 2015; Mendoza, 2021) to better detect their predators, who concentrate their period of activity at night (Finnegan et al., 2021; Foster et al., 2013). However, when sympatric with predators, collared peccaries can present overlap in their activities with predators (Azevedo et al., 2018; Gutiérrez‐González & López‐González, 2017; Zanin et al., 2020).…”

Effect of Nocturnal and Diurnal Moderate-intensity Swimming Exercise on Increasing Irisin Level of Female Mice (Mus musculus)

“…However, according to Algul et al (2017), the exact time to exercise for humans according to lifestyle (circadian rhythm) for health is still unknown, nor the time of exercise to burn body fat. Likewise, the exact time to exercise in mice is also not known (Mendoza et al, 2021). Nocturnal mice, unlike humans, sleep during the day and behave at night (Cajochen et al, 2003;Perreau-Lenz et al, 2004;Garidou-Boof et al, 2005).…”