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Lecture overview I. What are circadian rhythms II. Neuroanatomy of circadian rhythms III. Molecular biology of circad

Circadian rhythms. Free-running rhythm

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Lecture overview I. What are circadian rhythms II. Neuroanatomy of circadian rhythms III. Molecular biology of circad

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    1. Lecture overview I. What are circadian rhythms? II. Neuroanatomy of circadian rhythms III. Molecular biology of circadian rhythms

    2. Circadian rhythms Free-running rhythm “about” 24 hrs Characterized by phase and period Almost all functions entail a “homeostatic” regulation and a rhythmic regulation (e.g., appetite, sleep, etc.)

    3. Circadian rhythms Lesions of the suprachiasmatic nucleus (SCN) ablates free-running spontaneous circadian rhythms Homeostatic regulation remains intact

    4. Circadian rhythms What signals the SCN? Light, but also nutrition Depends on what is limiting, but nutrition dominates light

    5. SCN most identifiable structure in the hypothalamus: Compactly above OC

    6. SCN coordinates brain oscillators

    7. SCN coordinates autonomous oscillators

    8. Activation of SCN by light

    9. Normal phase advance in free-running conditions

    10. SCN lesion disrupts phase advance in free-running conditions

    11. Molecular basis of circadian rhythms First gene cloned: Per (flies w/o rhythms) Second gene cloned: CLOCK (mice w/o rhythms) Third gene: Cryptochrome (CRY) These genes produce transcriptional oscillations by a negative feedback loop (CLOCK positive, Per and Cry negative)

    18. Conclusions I. Most tissues exhibit spontaneous circadian oscillations, but these are rapidly lost without neuroendocrine coordination II. This spontaneous oscillation is subserved by the CLOCK/PER feedback system III. The SCN supplies the neuroendocrine coordination to reinforce these cycles

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