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Understanding Circadian Rhythm and Melanopsin: The Role of Light in Biological Timekeeping

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65 diapositives · 794 Views · Jul 17, 2014

This lecture delves into the fascinating world of circadian rhythms and the role of melanopsin in light detection. It explores how organisms adapt to the 24-hour light cycle, focusing on experiments measuring human eye resolution and activity patterns in mice. Students will learn about the importance of the superchiasmatic nucleus (SCN) in the hypothalamus and how light influences our biological clocks. The lecture also investigates the intriguing phenomenon of rodless and coneless mice, highlighting the diverse mechanisms of light sensitivity and circadian entrainment.

#understanding circadian rhythm and melanopsin: the role of light in biological timekeeping #understanding circadian rhythm and melanopsin: the role of light in biological timekeeping ppt #powerpoint #presentation
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  1. Lecture # 16 Circadian rhythm and melanopsin 3/28/13

  2. Measuring human eye resolution • Pick two of the four patterns in the hall – have each person in your group walk away from the pattern until you can’t see the stripes any more – measure distance to wall • Calculate your eye’s photoreceptor acceptance angle and your resolvable spatial frequency – put on board • Does it depend on the color combination?

  3. Human retinal mosaic

  4. Human retinal mosaic

  5. For next week – HW8Short (3 paragraphs) wiki page

  6. Chronobiology • How do organisms sense time of day? • Why do they need to do this?

  7. Circadian rhythm • Many organisms follow the 24 hr light cycle of the sun Circa = about + diem =day

  8. Light • Cycle needs to be entrained • Without light, cycle free runs • Loss of light at end of the day signals cycle • Why might cycle be useful?

  9. Measuring activity in mice Mice are nocturnal. Active at night and not during day During their active time, they will run on a wheel

  10. Wheel motion detector Monitor when and how much activity mouse has

  11. Monitor mouse activity - running on the wheel Day Night Lights on at 10 am and off at 10 pm

  12. Wheel running activity through the 24 hr day Light On Off

  13. Mouse wheel running – multiple days If you shift the light / dark boundary, it takes the mice a few days to shift back. They shift forward almost instantly If you remove the light, they still follow the 24 hour cycle.

  14. Mouse wheel running If you shift the light / dark boundary, it takes the mice a few days to shift back. They shift forward almost instantly If you remove the light, they still follow the 24 hour cycle.

  15. Jet lag aside

  16. If fly east to west 9 pm becomes 6 pm - darkness takes longer to come

  17. Mouse wheel running If day shifts later, your body adjusts almost immediately Easy to reset your clock to a later / longer time

  18. If fly west to east 6 pm becomes 9 pm - darkness comes sooner than you expect

  19. Mouse wheel running It takes your body a while to adjust to your clock getting shifted (shortened)

  20. How would mice detect light? ?????

  21. Non-mammals • Circadian detection occurs in the pineal organ • Pineal is on top of brain where it can easily receive light

  22. Mammals • Pineal is buried in mammalian brain • No obvious way to detect light

  23. Circadian rhythm • Human clock involves hypothalamus

  24. SCN is master controller of circadian clock - A few ganglion cells in eye project to SCN

  25. Setting the clock • Need eyes to set clock • Just a few of retinal ganglion cells project to SCN • SCN keeps master clock • The clock is set or photoentrained at twilight • Biological clock is set to local time • Zeitgeber = time giver

  26. Light detection • For 150 years people thought only rods and cones detected light in the vertebrate eye • Earliest eyes didn’t form images • Still sensitive to light

  27. Mice which lack rods and cones still have circadian rhythm!?!?!? Rodless/ coneless mice studied in early 1990’s Foster et al. 1991 Light

  28. The search #1. Find the light sensitive cells Science 295:1070 2002

  29. Berson et al 2002 • Inject dye into SCN in brain • Retrograde labeling of ganglion cells in retina • Measure light response of the labeled ganglion cells SCN = superchiasmatic nucleus

  30. Co+2 blocks rods and cones + drugs to block glutamate receptors

  31. Isolated cell Unlabeled Inject current

  32. Retinal neurons Photoreceptive retinal ganglion cell Special tract to hypothalamus and SCN

  33. Search #2: Find the visual pigmentMouse pupillary response Nature Neuroscience 4: 621

  34. Mouse pupillary response Pupil will constrict in response to light Mouse pupil can constrict a lot!

  35. Max pupil size Time course of pupil size responding to bright light is same in WT and rodless/coneless mice Lucas et al 2001

  36. Record action spectra • The pupil contractsin proportion to the amount it is stimulated • The stimulation is based on the amount of light it absorbs • Response should mirror pigment absorbance properties

  37. Light response • More light shine on eye, more pupil constricts • Plot % constriction vs light intensity • Find light intensity needed to give 50% response • Pigment absorption will be inversely proportional to this light intensity Pupil constriction Light intensity

  38. Action spectra Log irradiance (photons/cm2 s) Light intensity needed to make 50% constrict = sensitivity Measure at different wavelengths Plot sensitivity

  39. Action spectra Wild type Rodless- coneless

  40. Mouse visual pigments Cone: 360 and 508 nm; rod 498 nm

  41. Pupil response for rodless/conelessmice has different wavelength peak than rod/cone opsins The missing pigment

  42. Missing visual pigment • There must be a visual pigment with peak sensitivity at 480 nm • It must be in the retina • It is not in rods or cones • Controls multiple effects • Circadian entrainment • Pupillary response • Melatonin suppression

  43. Berson’s retinal ganglion cells which were light sensitive Photoreceptors Horizontal cells Bipolar cells Amacrine cells Ganglion cells

  44. Retinal ganglion cell response matches that of pigment causing pupil response Sensitivity has shape of pigment with λmax= 484 nm

  45. What is the visual pigment??

  46. Frog and fish melanophores respond to light – get smaller if light brighter

  47. Melanophores contain an opsin = melanopsin 7 transmembrane regions

  48. Melanophores contain an opsin = melanopsin Melanopsin is closest to insect opsins

  49. Melanopsin has broad expression in frogs Melanophores in skin Gives them light response Magnocellularpreoptic nucleus SCN

  50. Melanopsin is present in retina RGC containing melanopsin