1. MCB 186 CIRCADIAN BIOLOGY Slides Lecture 2 September 28, 2005 J. W. Hastings

2. CIRCADIAN RHYTHMS - KEY PROPERTIES (1)RHYTHMS CONTINUE IN ABSENCE OF LIGHT / DARK CYCLES WITH PERIODS CLOSE TO BUT NOT EXACTLY 24 HOURS exact period length is a function of environmental conditions (2)PERIOD IS TEMPERATURE “COMPENSATED”; ABOUT 24 HR AT DIFFERENT TEMPERATURES not temperature independent (3) PHASE can be RESET by LIGHT: RHYTHMS ENTRAINED or SYNCHRONIZED to DAILY ENVIRONMENTAL CYCLES resetting does not need cycles: single exposures or pulses suffice

3. RHYTHM IN HUMAN: LD & LL Raster Plots: - Single, double, triple etc. - Modulo tau

4. ALTERNATE to RASTER PLOT- PEAK # = CIRCADIAN DAYS

5. GONYAULAX APPARENT PHASE JUMPS OTHERWISE VERY PRECISE

6. ENTRAINMENT BY LIGHT-DARK CYCLE IN MONKEY MOORE-EDE ETAL

7. HUMAN CIRCADIAN ENTRAINMENT

8. GONYAULAX CELLS IN DD: PHASE SHIFT BY SINGLE LIGHT PULSES ADVANCE OR DELAY DEPENDS ON TIME IN CYCLE CONTROL IN DARK LATE NIGHT PULSE PHASE ADVANCE EARLY NIGHT PULSE PHASE DELAY

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

10. GONYAULAX PHASE ADVANCES BY LIGHT PULSES

11. GONYAULAX LIGHT PHASE RESPONSE CURVE (PRC)

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

13. GONYAULAX ACTION SPECTRUM FOR PHASE SHIFTING BY 3 HOUR LIGHT EXPOSURES

14. PHASE RESPONSE CURVE DESCRIBED MOORE-EDE ETAL

15. SCHEMATIC PHASE RESPONSE CURVES (PRCs )

16. Schematic depiction of entrainment by light: T constant, Tau changes

17. GONYAULAX ENTRAINMENT by 14 HR LD CYCLES, then DD or LL

18. ENTRAINMENT by DIFFERENT LIGHT/DARK CYCLES and EFFECT of LIGHT INTENSITY on LIMITS of ENTRAINMENT

19. LONG DAYS (LIGHT PERIOD) VERSUS SHORT DAYS LONG DAYS CAUSE BOTH DELAYS and ADVANCES SHORT DAYS ONLY ONE or the OTHER Phase angle (acrophase) differs with day length

20. LONG & SHORT DAY PHASE SHIFTS in an ORGANISM with a CIRCADIAN TAU OF 24.5 hr

21. ENTRAINMENT by T CYCLES with DIFFERENT PHOTOFRACTIONS

22. DROSOPHILA ENTRAINMENT TO FULL LD CYCLES PITTENDRIGH

23. SKELETON PHOTOPERIODS TWO LIGHT EXPOSURES (e.g., 15 min, or 1 hr each) EVERY CYCLE Longer dark interval (outside of 11-13) is self-selected as the night phase. 11-13 is the bistability region Cycles can be different from 24 hrs.

24. DROSOPHILA ECLOSION ACROPHASES with DIFFERENT INTERVALS for TWO-PULSE SKELETON PHOTOPERIODS Pittendrigh

25. BISTABILITY IN HAMSTER ENTRAINMENT SKELETON PHOTOPERIOD 13.5:0.25:10:0.25 hrs ANIMAL C15 ACTIVE INSHORT NIGHT TESTES MAINTAINED; ANIMAL C16 ACTIVE IN LONG NIGHT; TESTES REGRESSED

26. SINGLE PULSES EVERY 24h Sometimes 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

27. FREE RUNNING PERIOD HAMSTER ACTIVITY RHYTHM DEPENDS ON PERIOD OF SINGLE PULSE T CYCLE AND PULSE IS POSITIONED DIFFERENTLY