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Photoreceptors Regulating Circadian Behavior.

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Final rept. 15 Mar 92-14 Mar 95,

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In mammals circadian responses to light are regulated by photoreceptors within the eye. Aged rdrd mice 80-800 days show unattenuated circadian responses to light but lack visual responses, while rodless transgenic mice which lose rods earlier in development show increased circadian responses to light. These data indicate that rod photoreceptors are not required for photoentrainment, but the early loss of rods may affect the development of the entrainment pathway. Aged rdsrds mice, lacking rod and cone outer segments, show circadian photo-sensitivities indistinguishable from animals. The circadian system of aged rdrd mice shows spectral responses that are consistent with the involvement of the known mouse cone opsins green cone-511 nm UV cone-359 nm. Low levels of both the green and UV cone opsin mRNA remain with the eyes of aged rdrd mice. The subcutaneous eyes of the blind mole rat are used to regulate circadian responses to light. Preliminary data suggest that these eyes contain a single opsin that most closely resembles a green cone opsin. Collectively these data suggests that photoentrainment in mammals is mediated by cones. However, if the residual cones mediate circadian responses to light then very few are needed to maintain sensitivity and they do not require an outer segment.

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  • Anatomy and Physiology

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