mcb 186 circadian biology week 2 entrainment by light and the phase response curve (prc) september...
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MCB 186CIRCADIAN BIOLOGY
Week 2
Entrainment by light and the Phase Response Curve (PRC)
September 26, 2007J. W. Hastings
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) TEMPERATURE ALSO AFFECTS CIRCADIAN PERIOD BUT MUCH
LESS SO THAN FOR TYPICAL BIOCHEMICAL REACTIONS. Cellular
compensation is postulated to be responsible
(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
ENTRAINMENT OCCURS when ORGANISM is EXPOSED TO
LIGHT/DARK CYCLES
CAN BE CALLED SYNCHRONIZATION
OTHER CYCLES (e.g. temperature) CAN ALSO ENTRAIN
RHYTHM IN HUMAN: LD & LL
In LD the periodis exactly 24 hr
Variability in sleeponset has meaning
HUMAN CIRCADIAN ENTRAINMENT to LD and FREE RUNS
Phase shift
No evident jet lag
GONYAULAX RE-ENTRAINMENT TO A DIFFERENT PHASEHastings, 1958
controlNo jet lag ina unicellular organism
Cyanobacterial in vivo gene expression rhythm with bacterial luciferase as a reporter
Cells on two different LD cycles
24016814412096720
Hours in Constant Light
2000
4000
6000
8000
12 60 84 108 132 156 180
228
192
204
10000
48
Lu
min
esce
nce
Kondo, Johnson Golden et al., 1993, PNAS
ENTRAINMENT BY LIGHT-DARK CYCLE IN MONKEY
MOORE-EDE ETAL
Note that phase of free-run is determinedby point of release
LL
LD
LL
MASKING BY TEMP CYCLE- FLYING SQUIRREL DE COURSEY
An environmentalcycle can appearto entrain (masking)
Phase of rhythmAfter return to LL or DD reveals if itis masking
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
PERIOD (Tau) of CIRCADIAN RHYTHM DEPENDS on PRIOR L/D CYCLE PERIOD (T=20)
MOUSEPITTENDRIGH & DAAN
ENTRAINMENTto 20 hr CYCLEMUST be DONEGRADUALLY
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 intensity
Single cell organism: QUITE WIDE - 8 to 12 hrs
Higher organisms & humans: QUITE NARROW - 1 - 3 hr
LIMITS of ENTRAINMENT ILLUSTRATEDWHAT ARE the LIMITS DUE TO??
Figure 1 Wright et al, PNAS 2001
Human Melatonin Rhythms Under Different Weak Light Entrainment Cycles and then Forced Desynchrony
No entrainment
entrainsNo entrainment
23.5 hr 24 hr 24.6 hr
Fig 5 Gronfier et al, PNAS 2007
100 lux ENTRAINS while 25 lux DOES NOT
Relative Coordination in Hamster Activity in Light Intensity Cycle-length that Fails to Entrain Enright, 1980
Gonyaulax ENTRAINS to 14 HR LD CYCLESSubsequently on DD or LL, periods are about 24 hr
Note: tau ~24
ENTRAINMENT by DIFFERENT LIGHT/DARK CYCLES and EFFECT of LIGHT INTENSITY on LIMITS of ENTRAINMENT
12 hr cycle entrains athigh but not low lightintensity - because phaseshifts are greater at highlight intensity
Note that period revertsto ~ 24 hr in subsequentLLHastings & Sweeney, 1959
Wever R. Int J Chronobiol 3: 19, 1975
Free-running Human Subject Demonstrating Spontaneous Switch From “Internally Synchronized Rhythms” to “Internal Desynchronization”
Time (hours)T
ime
(day
s)
Temperature
Sleep-wake
DINOFLAGELLATE FLASH & GLOW BIOLUMINESCENCEand its CIRCADIAN EXPRESSION
scale: ~ 24 hours peak to peak
DIFFERENT OSCILLATORS CONTROL GLOW & FLASHING
Internnal Desynchronization
NIGHT PHASE: LAWN ON BOTTOM OF DISH (LEFT)DAY PHASE: AGGREGATIONS (RIGHT)
GONYAULAX CIRCADIAN RHYTHM OF AGGREGATION / ACTIVITY
GONYAULAX INTERNAL DESYNCHRONIZATION OF TWO RHYTHMSROENNEBERG
THREE RHYTHMS SIMULTANEOUSLY: PHASE-JUMPS ROENNEBERG & MORSE 1993
Glo
Fls Agg
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
Gonyaulax CELLS IN DD: PHASE SHIFT BY SINGLE LIGHT PULSESADVANCE OR DELAY DEPENDS ON TIME IN CYCLE
CONTROL IN DARK
LATE NIGHT PULSEPHASE ADVANCE
EARLY NIGHT PULSEPHASE DELAY
Hastings and Sweeney, 1958
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) Hastings & Sweeney, 1958
Gonyaulax LIGHT PHASE RESPONSE CURVE (the PRC)LIGHT PULSES GIVEN AT TIMES INDICATED
TIME 0 is theBEGINNING ofNIGHT PHASE
DEAD ZONEDAY PHASE
DROSOPHILA PHASE RESPNSE CURVE PITTENDRIGH
TIME 12 is theBEGINNING ofNIGHT PHASE
PRCs in Gonyaulax: LIGHT-INDUCED DELAY-PHASE SHIFTS ARE INCREASED BY CREATINE
PHASE RESPONSE CURVES (PRCs) in the MOSQUITO
Single Light Pulses Given at Different Times to Animals in DD Cause Delay or Advance Phase Shifts:PRC Moore-Ede et al 1982
Schematic depiction of entrainment by light in LD
different Tau values : T constant, 24h
• 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
EMERGENCE TIMES of DROSOPHILA ENTRAINED to FULL LD CYCLES OF DIFFERENT PHOTOFRACTIONS
PITTENDRIGH
PHASE JUMP with DIFFERENT SKELTON PHOTOPERIODSECLOSION OCCURS AFTER THE LONGER DARK INTERVAL
DROSOPHILA ECLOSION PHASE ANGLES with DIFFERENT INTERVALS for TWO-PULSE SKELETON PHOTOPERIODS
Pittendrigh
Hamster Phase Angle of Entrainment in Complete and Skeleton Photoperiods Pittendrigh & Daan, 1976
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
A SINGLE PULSE per CYCLE WILL ENTRAIN PERIOD of ACTIVITY RHYTHM DEPENDS on PERIOD of SINGLE PULSE T-CYCLE: POSITIONING of PULSE is
SELF-SELECTED