Circadian Photoreception in Humans and Mice

Circadian rhythms have a periodicity of approximately twenty-four hours in mammals.

• Circadian rhythms in mammals are synchronized to the daily light-dark cycle through light input via the eye.
• Classical opsins in outer retinal photoreceptor cells are essential for vision but not necessary for circadian photoreception.
• Mammalian cryptochromes and melanopsin are proposed as key circadian photoreceptor pigments located in the inner retina.
• Genetic analysis suggests that cryptochromes are the primary photoreceptors for regulating circadian rhythms.
• Classical photoreceptors and melanopsin may have overlapping roles in maintaining circadian rhythmicity.

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