The Regulation of Mammalian Circadian Physiology by Light.
Final rept. 15 Mar 95-14 Mar 97
VIRGINIA UNIV CHARLOTTESVILLE DEPT OF BIOLOGY
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The sensory demands of photoentrainment have imposed a unique set of selection pressures, which have led to the evolution of specialised photoreceptor systems. Our work studies on retinally degenerate mammals have shown that visual blindness need not mean circadian blindness, and that two functionally distinct systems for processing light information must exits within the mammal eye. An image-forming system, which constructs an representation of the environment, and a non-image-forming photoreceptor system, which deduces gross changes in the overall amount of light at different times of day. specialisations of the mammalian photoentrainment pathway include a distinct set of retinal ganglion cells that project exclusively to the circadian centres within the brain, and the possible utilisation novel ocular photoreceptors. The features of the light environment that mediate entrainment have yet to be fully defined. Environmental irradiance appears to be a critical influence, but spectral changes andor the position of the sun could theoretically provide useful information about the phase of twilight. Finally the extent to which expressed circadian rhythms arise directly from a clock, or are the products or an interacting between a clock and the entrainment pathway, remains unclear in the vertebrates. In mammals at least, major lesions to the retina, at a time when both the retina and SCN are developmentally plastic, appear to markedly influence some aspects of the circadian phenotype.
- Anatomy and Physiology
- Medicine and Medical Research