MCB 186 CIRCADIAN BIOLOGY Slides Lecture 2 September 28, 2005 J. W. Hastings.
-
date post
19-Dec-2015 -
Category
Documents
-
view
214 -
download
1
Transcript of MCB 186 CIRCADIAN 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
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 LIGHT PHASE RESPONSE CURVE (the PRC)LIGHT PULSES GIVEN AT TIMES INDICATED
TIME 0 is theBEGINNING ofNIGHT PHASE
DEAD ZONEDAY PHASE
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
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