Effects of Daytime Blue-Enriched LED Light on Physiologic Parameters of Three Common Mouse Strains Maintained on an IVC System

Light: An Extrinsic Factor Influencing Animal-based Research

Light is an environmental factor that is extrinsic to animals themselves and that exerts a profound influence on the regulation of circadian, neurohormonal, metabolic, and neurobehavioral systems of all animals, including research animals. These widespread biologic effects of light are mediated by distinct photoreceptors-rods and cones that comprise the conventional visual system and melanopsin-containing intrinsically photosensitive retinal ganglion cells (ipRGCs) of the nonvisual system that interact with the rods and cones. The rods and cones of the visual system, along with the ipRGCs of the nonvisual system, are species distinct in terms of opsins and opsin concentrations and interact with one another to provide vision and regulate circadian rhythms of neurohormonal and neurobehavioral responses to light. Here, we review a brief history of lighting technologies, the nature of light and circadian rhythms, our present understanding of mammalian photoreception, and current industry practices and standards. We also consider the implications of light for vivarium measurement, production, and technological application and provide simple recommendations on artificial lighting for use by regulatory authorities, lighting manufacturers, designers, engineers, researchers, and research animal care staff that ensure best practices for optimizing animal health and well-being and, ultimately, improving scientific outcomes.

Vivarium Lighting as an Important Extrinsic Factor Influencing Animal-based Research

Light is an extrinsic factor that exerts widespread influence on the regulation of circadian, physiologic, hormonal, metabolic, and behavioral systems of all animals, including those used in research. These wide-ranging biologic effects of light are mediated by distinct photoreceptors, the melanopsin-containing intrinsically photosensitive retinal ganglion cells of the nonvisual system, which interact with the rods and cones of the conventional visual system. Here, we review the nature of light and circadian rhythms, current industry practices and standards, and our present understanding of the neurophysiology of the visual and nonvisual systems. We also consider the implications of this extrinsic factor for vivarium measurement, production, and technological application of light, and provide simple recommendations on artificial lighting for use by regulatory authorities, lighting manufacturers, designers, engineers, researchers, and research animal care staff that ensure best practices for optimizing animal health and wellbeing and, ultimately, improving scientific outcomes.

Influence of Light Phase Exposure to LED Lighting on Circadian Levels of Neuroendocrine Hormones in Sprague-Dawley Rats

Light and lighting protocols of animal research facilities are critically important to the outcomes of biomedical research that uses animals. Previous studies from our laboratory showed that the wavelength (color) of light in animal housing areas affects the nocturnal melatonin signal that temporally coordinates circadian rhythms in rodents. Here, we tested the hypothesis that exposure to LED light enriched in the blue-appearing portion (460-480 nm) of the visible spectrum during the light phase (bLAD) influences circadian concentrations of select neuroendocrine hormones in adolescent Sprague-Dawley rats. Male and female rats (4 to 5 wk old) were housed on a novel IVC system under a 12L:12D in either cool-white fluorescent (control, n = 72) or bLAD (experimental, n = 72) lighting. Every third day, body weight and food and water consumption were measured. On Day 30, rats were anesthetized with ketamine/xylazine and terminal collection of arterial blood was performed to quantify serum concentrations of melatonin, corticosterone, insulin, and glucose at 6 circadian time points (0400, 0800, 1200, 1600, 2000, 2400). As compared with male and female rats housed under cool white fluorescent (CWF) lighting, rats in bLAD lighting showed a 6-fold higher peak in dark phase serum melatonin (P < 0.05). Effects on serum corticosterone were sex dependent, as CWF and bLAD females had significantly higher corticosterone levels than did CWF and bLAD males, respectively. CWF and bLAD females had significantly higher serum glucose overall as compared with males. However, serum insulin was not affected by sex (M or F) or lighting conditions (CWF or bLAD). These data show that housing Sprague-Dawley rats under bLAD lighting conditions increases circadian peaks of melatonin without increasing serum levels of corticosterone, glucose or insulin, indicating less variation of circadian cycling of key neuroendocrine hormones in bLAD-exposed rats.