Red Light at Night: Identifying Unexpected Sources of Circadian Disruptions Rats that are exposed to nighttime red light are more likely to manifest SCN activation than rats that are not exposed to red light.

Undergraduate Honors Thesis

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Citeable URL: https://scholar.colorado.edu/concern/undergraduate_honors_theses/g732db04s

Abstract

Laboratory rats are often used as model organisms to study a wide variety of mammalian neurological and physiological processes. As most rodent research is conducted during daylight hours and laboratory rats are nocturnal, the behavioral outcomes of many experiments may become skewed by requiring that rodents perform during their inactive phase. The solution is to conduct experiments during the animal's active phase, in darkness. However, this would make vision difficult for the experimenter. Consequently, experimentation is commonly practiced under red light conditions. There is a widely held belief that the rat visual system is insensitive to red wavelengths of light (>575 nm); however, recent studies have shown that the rat's visual system also responds to red wavelengths of light. My study shows that nighttime red light exposure also activates the suprachiasmatic nucleus of the hypothalamus (SCN), the master biological clock, even after a one minute of exposure. This effect may result from retinal detection of red light wavelengths and activation of intrinsically photosensitive retinal ganglion cells (ipRGCs), whose axons project to the SCN through a non-image-forming neural pathway known as the retinohypothalamic tract. These results emphasize the necessity to reconsider red light nighttime testing in rodent research.

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