Circadian Rhythms and the
Biological Clock:
An Historical Introduction
Outline
• What are Circadian Rhythms?
• Why do we call the mechanism that regulates
circadian rhythms a “Biological Clock”?
What are the Important Characteristics
of a “Clock”?
1. It can be set to local time
2. It can tell you the time of day.
3. It can be used to measure lapse of time
A Human Sleep Wake Cycle
in the Laboratory
24-h Day
25-h Day
24-h Day
Unscheduled Day
Human Isolation Chamber
in Sapporo Japan
Charles Czeisler
Jurgen Aschoff
Circadian (Circa, Dies) Rhythms are Ubiquitous
in Living Systems and Have Similar Properties
Circadian Rhythms: The Basic Model
+
=
Light Cycle
Entrained
Rhythm
Freerunning
Rhythm
Origins of the Field of “Chronobiology”: Early
Observations of Daily Rhythms in Plants
The first written record: In the 4th century BC Adrosthenes, a scribe for Alexander
the Great, wrote that he observed on the march to India that the leave of the
tamarind tree always opened during the day and closed at night.
Scarlet Pimpernel
Day
Night
The first hint that daily rhythms
are internally driven
Daily rhythms of
"sleep movements"
of leaves (Mimosa).
Jean-Jacques deMairan’s
Experiment (1729)
“The progress of true science, which
is the experimental kind, is
necessarily slow”
The Next 200 Years
•1832 de Candolle discovers that the Mimosa opens
it’s leaves 1-2 hours earlier each day
•1906 Simpson and Gailbraith find daily temperature
rhythms in monkeys persist in constant darkness
•1922 Richter shows persistent rhythms of activity
in animals (rats)
The Birds
And the Bees
Recognizing Local Time of Day
Karl von Frisch
Daily Rhythms in Nectar Secretion
Porcelainflower
Daily rhythm of nectar secretion in
Hoya carnosa. Matile, P, (2005)
Bee visits to a crookneck squash
patch (peak nectar production at
9:00 AM) Edge et al. (2012)
No News to the Poets!
Andrew Marvell (1621-1678)
from Thoughts in a Garden
“And as it works, the industrious bee
computes its time as well as we.
How could such sweet and wholesome hours
be reckoned but with herbs and flowers”
Dance Language of the Bees: Measuring Lapse of Time
The Round
Dance
When a bee finds a
food source some
distance from the
hive, he can return to
the hive and, through
dance, can
communicate the
direction (with
respect to the sun)
and the distance of
the food source. The
movement of the sun
across the sky is
compensated for by
the bee’s internal,
biological clock.
The Waggle
Dance
A vertical waggle
indicates directly
towards the sun
Time Compensated
Sun Compass
Orientation
Sun Orientation in Starlings
Gustave Kramer 1950
Klaus Hoffman 1960
Circadian Clocks and Sun-Compass
Orientation
“Photoperiodism” and Measuring
Daylength
Garner & Allard, 1920
Fall (Short Day)
Summer (Long Day)
Photoperiodic Time Measurement in a Hamster
Michael Menaker
Pineal Gland & Melatonin
•
•
Released from the pineal gland at night. In mammals, synthesis and release are
controlled by the Biological Clock.
In many mammals it is involved in regulating seasonal cycles that are controlled by
the length of the daily photoperiod (reproduction, coat color, fat accumulation,
hibernation, etc.)
Siberian Hamsters from long days/short nights
(summer) and short days/long nights (winter).
•
Testes from Long-day and Short-day hamsters
In humans melatonin’s function is not yet fully understood, though in the popular
press it has been touted as a cure for everything from insomnia to Alzheimer’s
disease.
The Problem of Temperature
Early Studies of Human Circadian Rhythms
Siffre’s Cave Experiment
in Texas, 1972. He
emerged after 179 days,
but he thought he had
been in the cave for only
151 days
http://www.bgamplifier.com/lifestyle/newsreel-sleep-experiment-in-mammoth-cave/youtube_dc3b38ce-f3a9-11e2-b516-0019bb2963f4.html