1. Circadian Rhythms and the Biological Clock: An Historical Introduction

2. Outline What are Circadian Rhythms?
Why do we call the mechanism that regulates circadian rhythms a “Biological Clock”?

3. What are the Important Characteristics of a “Clock”?
It can be set to local time
It can tell you the time of day.
It can be used to measure lapse of time

4. A Human Sleep Wake Cycle in the Laboratory
24-h Day
25-h Day
Unscheduled Day
Human Isolation Chamber
in Sapporo Japan
Charles Czeisler
Jurgen Aschoff

5. Circadian (Circa, Dies) Rhythms are Ubiquitous in Living Systems and Have Similar Properties

6. Circadian Rhythms: The Basic Model+ =
Light Cycle
Entrained
Rhythm
Freerunning
Rhythm

7. 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

8. 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”

9. 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)

10. The Birds
And the Bees

11. Recognizing Local Time of Day
Karl von Frisch

12. 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)

13. No News to the Poets!
Andrew Marvell ( ) 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”

14. Dance Language of the Bees: Measuring Lapse of Time
The Round Dance
The Waggle 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.
A vertical waggle indicates directly towards the sun
Time -CompensatedSun Compass Orientation

15. Sun Orientation in Starlings
Gustave Kramer 1950
Klaus Hoffman 1960

16. Circadian Clocks and Sun-Compass Orientation

17. “Photoperiodism” and Measuring Daylength
Garner & Allard, 1920
Fall (Short Day)
Summer (Long Day)

18. Photoperiodic Time Measurement in a Hamster
Michael Menaker

19. 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.

20. The Problem of Temperature

21. Early Studies of Human Circadian Rhythms
Siffre’s Cave Experiment in Texas, He emerged after 179 days, but he thought he had been in the cave for only 151 days