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”? It can be set to local time It can tell you the time of day. It can be used to measure lapse of time

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

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 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

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