MCB 186CIRCADIAN BIOLOGY

Slides Lecture 2 September 28, 2005

J. 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) 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

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 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.

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