Organization of behavior and biological rhythms
How do animals organize their behavior through time?
What is organized?
Are the rhythms exogenous or endogenous?
Central question is whether rhythms persist in the absence of time cues.
Is the clock a single tissue or is every tissue a clock?
Location of the master clock:
suprachiasmatic nucleus (SCN)
Evidence for a master clock - Hamster SCN transplant experiment
Lesion SCN of 20 hour period mutant - results in
(see Fig. 1E)
Transplant fetal SCN tissue of 22 hour period mutant
Circadian rhythm is restored with period of 22 hours
Other tissues (all tissues?) show circadian rhythmicity in culture
Molecular basis of circadian rhythms is now understood to be the result of a
complex system of transcriptional-translational autoregulatory loops
SCN coordinates the output of cellular clocks to produce synchronous activity throughout all tissues of the body
Zeitgeber = German for "time giver"
Light is primary signal
Photoreceptors in retina (pigment=
Non-mammals also have extraretinal photoreceptors (e.g.,
Why don't mammals have extraretinal photoreceptors?
Nocturnal bottleneck theory
Other types of signals may influence other tissues
Food -> liver
Exposure to zeitgeber changes onset of next cycle depending on
when it occurs
(shortens current cycle; next "day" starts sooner)(see Fig. 4B)
(lengthens current cycle; next "day" starts later)(see Fig. 4 A)
on how phase response curves are created and how they enable us to predict the effect that a brief exposure to a zietgeber with have on activity rhythms.
Why have entrainment?
on endogenous activity rhythms in humans