About this Research Topic
Light entering the eyes interacts with visual areas in the brain making visible our surroundings and constituting one of the main sensory inputs for the body. Furthermore, through a non-visual retinohypothalamic pathway, light synchronizes the circadian rhythms generated by the central pacemaker located in the suprachiasmatic nuclei (SCN) of the hypothalamus; in that way, both physiological and behavioral responses are adapted to the geophysical day. Such responses depend on an adequate light intensity and biological time exposure to modulate the SCN. Insufficient or desynchronized light alters the proper functioning of the master clock affecting gene expression, neuronal survival in its target areas, physiological parameters, mood and behavior, and might increase the risk of cancer, cardiovascular diseases, etc., in both laboratory animals and humans. Although these light effects are generally well known, in practice the implications of an insufficient exposure are mostly considered for visual tasks. Most researchers, caregivers and animal providers dismiss the nonvisual biological effect of light and its impact on health, and expose the experimental subjects to non-uniform and uncontrolled light intensity. As mentioned before, the timing of light exposure is also critical, and the emerging field of “light at night” studies provide compelling evidence for the deleterious effect of nocturnal illumination in humans.
The aim of this Research Topic is to compile key information bringing together original research, methods, hypotheses and theory, opinions, etc. to provide the reader with a foundation for understanding the relevance of adequate lighting conditions (natural and artificial light) in any kind of study and species of animal. We also welcome researchers from the biological rhythm field to discuss the validity of those studies performed under a “free-running state”, since in rodents long-term constant darkness causes significant apoptosis in monoaminergic systems in association with a behavioral depressive phenotype, inflammatory processes with reduced hippocampal cell proliferation and altered activity of the local clock genes.
Some of the questions we propose to address are: What are the consequences of insufficient intensity or altered timing of light on general health parameters? What are the mechanisms for the effects of untimed light exposure (e.g., light at night) on neurological and physiological variables? How reliable or biologically relevant are experiments performed under constant dark or constant light conditions? Does light have trophic effects on the brain? What other neurological functions can be attributed to non-visual effects of light?
Finally, our aim is to also make a call to the scientific community in order to “use” light to transform husbandry settings into healthier environments to assure the welfare of the laboratory animals and therefore improve the experimental outcomes.
Keywords: Light, suprachiasmatic nucleus, depression, biological rhythms, lighting conditions, husbandry
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