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MCB 186 CIRCADIAN BIOLOGY Slides Lecture 2 September 28, 2005 J. W. Hastings. CIRCADIAN RHYTHMS - KEY PROPERTIES. 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 - PowerPoint PPT Presentation
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MCB 186CIRCADIAN BIOLOGY
Slides Lecture 2 September 28, 2005
J. W. Hastings
CIRCADIAN RHYTHMS - KEY PROPERTIES
(1) RHYTHMS CONTINUE IN ABSENCE OF LIGHT / DARK CYCLESWITH PERIODS CLOSE TO BUT NOT EXACTLY 24 HOURS
exact period length is a function of environmental conditions
(2) PERIOD IS TEMPERATURE “COMPENSATED”; ABOUT 24 HRAT DIFFERENT TEMPERATURES
not temperature independent
(3) PHASE can be RESET by LIGHT: RHYTHMS ENTRAINED or SYNCHRONIZED to DAILY ENVIRONMENTAL CYCLESresetting does not need cycles: single exposures or pulses suffice
RHYTHM IN HUMAN: LD & LL
Raster Plots:- Single, double, triple etc.- Modulo tau
ALTERNATE to RASTER PLOT- PEAK # = CIRCADIAN DAYS
GONYAULAX APPARENT PHASE JUMPSOTHERWISE VERY PRECISE
ENTRAINMENT BY LIGHT-DARK CYCLE IN MONKEY MOORE-EDE ETAL
HUMAN CIRCADIAN ENTRAINMENT
GONYAULAX CELLS IN DD: PHASE SHIFT BY SINGLE LIGHT PULSESADVANCE OR DELAY DEPENDS ON TIME IN CYCLE
CONTROLIN DARK
LATE NIGHT PULSEPHASE ADVANCE
EARLY NIGHT PULSEPHASE DELAY
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??
GONYAULAX PHASE ADVANCES BY LIGHT PULSES
GONYAULAX LIGHT PHASE RESPONSE CURVE (PRC)
GONYAULAX LIGHT PHASE RESPONSE CURVE (the PRC)LIGHT PULSES GIVEN AT TIMES INDICATED
TIME 0 is theBEGINNING ofNIGHT PHASE
DEAD ZONEDAY PHASE
GONYAULAX ACTION SPECTRUM FOR PHASE SHIFTING BY 3 HOUR LIGHT EXPOSURES
PHASE RESPONSE CURVE DESCRIBED MOORE-EDE ETAL
SCHEMATIC PHASE RESPONSE CURVES (PRCs)
Schematic depiction of entrainment by light: T constant, Tau changes
GONYAULAX ENTRAINMENT by 14 HR LD CYCLES, then DD or LL
ENTRAINMENT by DIFFERENT LIGHT/DARK CYCLES and EFFECT of LIGHT INTENSITY on LIMITS of ENTRAINMENT
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
LONG & SHORT DAY PHASE SHIFTS in an ORGANISM with a CIRCADIAN TAU OF 24.5 hr
ENTRAINMENT by T CYCLES with DIFFERENT PHOTOFRACTIONS
DROSOPHILA ENTRAINMENT TO FULL LD CYCLES PITTENDRIGH
SKELETON PHOTOPERIODSTWO 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.
DROSOPHILA ECLOSION ACROPHASES with DIFFERENT INTERVALS for TWO-PULSE SKELETON PHOTOPERIODS
Pittendrigh
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
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
FREE RUNNING PERIOD HAMSTER ACTIVITY RHYTHM DEPENDS ON PERIOD OF SINGLE PULSE T CYCLE AND
PULSE IS POSITIONED DIFFERENTLY