CIRCADIAN RHYTHMS - KEY PROPERTIES

1. MCB 186CIRCADIAN BIOLOGYWeek 2Entrainment by light and the Phase Response Curve (PRC)September 26, 2007J. W. Hastings

2. CIRCADIAN RHYTHMS - KEY PROPERTIES RHYTHMS CONTINUE IN ABSENCE OF LIGHT / DARK CYCLESWITH PERIODS CLOSE TO BUT NOT EXACTLY 24 HOURSexact period length is a function of environmental conditions TEMPERATURE ALSO AFFECTS CIRCADIAN PERIOD BUT MUCH LESS SO THAN FOR TYPICAL BIOCHEMICAL REACTIONS. Cellular compensation is postulated to be responsible PHASE can be RESET by LIGHT: RHYTHMS ENTRAINED or SYNCHRONIZED to DAILY ENVIRONMENTAL CYCLESresetting does not need cycles: single exposures or pulses suffice

3. ENTRAINMENT OCCURS when ORGANISM is EXPOSED TO LIGHT/DARK CYCLES CAN BE CALLED SYNCHRONIZATION OTHER CYCLES (e.g. temperature) CAN ALSO ENTRAIN

4. RHYTHM IN HUMAN: LD & LL In LD the period is exactly 24 hr Variability in sleep onset has meaning

5. HUMAN CIRCADIAN ENTRAINMENT to LD and FREE RUNS Phase shift No evident jet lag

6. control GONYAULAX RE-ENTRAINMENT TO A DIFFERENT PHASEHastings, 1958 No jet lag in a unicellular organism

7. Cyanobacterial in vivo gene expression rhythm with bacterial luciferase as a reporter Cells on two different LD cycles Luminescence Kondo, Johnson Golden et al., 1993, PNAS

8. ENTRAINMENT BY LIGHT-DARK CYCLE IN MONKEY MOORE-EDE ETAL LL LD LL Note that phase of free-run is determined by point of release

9. MASKING BY TEMP CYCLE- FLYING SQUIRREL DE COURSEY An environmental cycle can appear to entrain (masking) Phase of rhythm After return to LL or DD reveals if it is masking

10. CAN ORGANISMS ENTRAIN to CYCLE LENGTHS OTHER THAN 24 hr?HOW DO THEY ENTRAIN TO DIFFERENT PHOTO-FRACTIONS e.g., LD 6:18 or 18:6

11. PERIOD (Tau) of CIRCADIAN RHYTHM DEPENDS on PRIOR L/D CYCLE PERIOD (T=20) MOUSE PITTENDRIGH & DAAN ENTRAINMENT to 20 hr CYCLE MUST be DONE GRADUALLY

12. ARE THERE “LIMITS” to CYCLE LENGTHS that can ENTRAIN?Yes, but these differ widely depending on the effectiveness of light in causing phase shifts: effectiveness depends on intensitySingle cell organism: QUITE WIDE - 8 to 12 hrsHigher organisms & humans: QUITE NARROW - 1 - 3 hr

13. LIMITS of ENTRAINMENT ILLUSTRATEDWHAT ARE the LIMITS DUE TO??

14. Human Melatonin Rhythms Under Different Weak Light Entrainment Cycles and then Forced Desynchrony 24 hr 24.6 hr 23.5 hr No entrainment entrains No entrainment Figure 1 Wright et al, PNAS 2001

15. 100 lux ENTRAINS while 25 lux DOES NOT Fig 5 Gronfier et al, PNAS 2007

16. Relative Coordination in Hamster Activity in Light Intensity Cycle-length that Fails to Entrain Enright, 1980

17. Gonyaulax ENTRAINS to 14 HR LD CYCLESSubsequently on DD or LL, periods are about 24 hr Note: tau ~24

18. ENTRAINMENT by DIFFERENT LIGHT/DARK CYCLES and EFFECT of LIGHT INTENSITY on LIMITS of ENTRAINMENT 12 hr cycle entrains at high but not low light intensity - because phase shifts are greater at high light intensity Note that period reverts to ~ 24 hr in subsequent LL Hastings & Sweeney, 1959

19. Free-running Human Subject Demonstrating Spontaneous Switch From “Internally Synchronized Rhythms” to “Internal Desynchronization” Time (hours) Time (days) Sleep-wake Temperature Wever R. Int J Chronobiol 3: 19, 1975

20. DINOFLAGELLATE FLASH & GLOW BIOLUMINESCENCEand its CIRCADIAN EXPRESSION scale: ~ 24 hours peak to peak

21. DIFFERENT OSCILLATORS CONTROL GLOW & FLASHING Internnal Desynchronization

22. NIGHT PHASE: LAWN ON BOTTOM OF DISH (LEFT)DAY PHASE: AGGREGATIONS (RIGHT)

23. GONYAULAX CIRCADIAN RHYTHM OF AGGREGATION / ACTIVITY

24. GONYAULAX INTERNAL DESYNCHRONIZATION OF TWO RHYTHMSROENNEBERG

25. THREE RHYTHMS SIMULTANEOUSLY: PHASE-JUMPS ROENNEBERG & MORSE 1993 Fls Agg Glo

26. ENTRAINMENT is due to PHASE SHIFTS in CIRCADIAN RHYTHM BUT PHASE SHIFTS do not REQUIRE FULL LIGHT/DARK CYCLES REPEATED “BRIEF” EXPOSURES TO LIGHT SUFFICE THE PHASE RESPONSE CURVE- PRC

27. Hastings and Sweeney, 1958 Gonyaulax CELLS IN DD: PHASE SHIFT BY SINGLE LIGHT PULSESADVANCE OR DELAY DEPENDS ON TIME IN CYCLE LATE NIGHT PULSE PHASE ADVANCE EARLY NIGHT PULSE PHASE DELAY CONTROL IN DARK

28. HOW DOES ONE DISTINGUISH DELAYS from ADVANCES?GIVE a STRONGER(BRIGHTER) EXPOSURE to LIGHTTHIS RESULTS in a GREATER PHASE SHIFT - but in WHICH DIRECTION??

29. GONYAULAX PHASE ADVANCES BY LIGHT PULSES

30. GONYAULAX LIGHT PHASE RESPONSE CURVE (PRC) Hastings & Sweeney, 1958

31. Gonyaulax LIGHT PHASE RESPONSE CURVE (the PRC)LIGHT PULSES GIVEN AT TIMES INDICATED DEAD ZONE DAY PHASE TIME 0 is the BEGINNING of NIGHT PHASE

32. DROSOPHILA PHASE RESPNSE CURVE PITTENDRIGH TIME 12 is the BEGINNING of NIGHT PHASE

33. PRCs in Gonyaulax: LIGHT-INDUCED DELAY-PHASE SHIFTS ARE INCREASED BY CREATINE

34. PHASE RESPONSE CURVES (PRCs) in the MOSQUITO

35. Single Light Pulses Given at Different Times to Animals in DD Cause Delay or Advance Phase Shifts:PRC Moore-Ede et al 1982

36. Schematic depiction of entrainment by light in LD different Tau values: T constant, 24h

37. CAN ORGANISMS ENTRAIN to CYCLE LENGTHS OTHER THAN 24 hr?HOW DO THEY ENTRAIN TO DIFFERENT PHOTO-FRACTIONS e.g., LD 6:18 or 18:6

38. EMERGENCE TIMES of DROSOPHILA ENTRAINED to FULL LD CYCLES OF DIFFERENT PHOTOFRACTIONS PITTENDRIGH

39. PHASE JUMP with DIFFERENT SKELTON PHOTOPERIODSECLOSION OCCURS AFTER THE LONGER DARK INTERVAL

40. DROSOPHILA ECLOSION PHASE ANGLES with DIFFERENT INTERVALS for TWO-PULSE SKELETON PHOTOPERIODSPittendrigh

41. Hamster Phase Angle of Entrainment in Complete and Skeleton Photoperiods Pittendrigh & Daan, 1976

42. SINGLE PULSES EVERY 24hSometimes called T-cycles A single light pulse (e.g., 15 min, 1hr) every cycle will entrain a circadian rhythm. Cycle may be =24h, longer or shorter than 24 Organism self selects location of light pulse If tau is greater than 24 it will fall at late night If tau is less than 24 it will fall at early night

43. A SINGLE PULSE per CYCLE WILL ENTRAINPERIOD of ACTIVITY RHYTHM DEPENDS on PERIOD of SINGLE PULSE T-CYCLE: POSITIONING of PULSE is SELF-SELECTED