Journal of Heredity 2004:95(1)
© 2004 The American Genetic Association 95:91-92
Book Review |
Chronobiology: Biological Timekeeping
J. C. Dunlap, J. J. Loros, and P. J. DeCoursey, Editors.Sinauer Associates, Sunderland, Massachusetts. 2004.
This large book is the ultimate result of a conference held at Dartmouth in 2001. It is superbly edited, richly illustrated, and in 11 chapters, it comprises the presentations by experts in this interesting field. Of the many books I get to read, this has been the most rewarding and I cannot stress enough how much future readers would be rewarded by acquiring this fascinating volume.
What is time? DeCoursey sets the stage by reviewing the origin of human timekeeping and the emergence of chronobiology as a discipline in the last century. The "Zeitgedächtnis" has long been a puzzle to scientists, but it was not until less than 100 years ago that substantial progress began by the creation of the discipline "chronobiology." The two principal protagonists of this effort, Pittendrigh and Aschoff, are given appropriate attention not only in the first chapter, but throughout the book. The volume provides a marvelous overview of the evolution of thinking about biological regulation of rhythms. The general terminology used in this discipline, such as "free-running," "circadian rhythm," "pacemaker," "Zeitgeber," etc., are introduced. Each chapter concludes with a concise summary and a series of challenging "study questions" that are useful to focus one's mind on the topics that have been discussed in such great detail.
Following this most readable introduction, the subsequent chapters gradually discuss the increasing complexity of rhythms found in bacteria, plants, insects, various mammals, and eventually we learn of the impact on human activities. Among many examples I could give, there are considerations of the light receptors of birds, reptiles, and mammals, the dependence of a circadian timer for the Zeitgedächtnis in bees is highlighted, the transfer of melatonin to fetal hamsters is discussed, effects of pinealectomy, the as yet unknown target sites of melatonin, and especially the variably located sites of the perception of light and effector mechanisms are described in great detail. Of considerable importance in all of the chapters is the profusion of illustrative diagrams and the results from actual experiments.
Chapters discuss how bats, living in dark cages, find the right time to emerge; how rodents, rapidly flown across time zones, readjust their rhythm; how entrainment to the circadian cycle works in general; and numerous specific examples are described in detail. Drosophila mutants and retinal organization in frogs are described with relevance to cylicity, and the wide differences existing in reptiles and birds are explored. But eventually we come to the location of the mammalian oscillator and to its location in man, where it is located principally in the suprachiasmatic nucleus. The many sophisticated experiments to study its physiology, entrainment, and the molecular mechanisms of feedback loops that exist in bacteria, as well as the clock-controlled genes are explored in detail. But finally we really might want to know, how does all of this affect human circadian rhythms (24.3 h), what are the endocrine sequelae, and what are the effects of disturbed circadian cycles in complex life styles (air pilots, nightshift nurses, doctors, travelers) on human performance? The prologue of chapter 9 says: "Not only do humans disregard clock signals, but they created their own environments, in places as bizarre as underground caves in the Antarctic ice sheet or gigantic work stations in outer space." These places have served as unique experimental laboratories for the study of circadian rhythm control and entrainment. As one who has regularly taken melatonin when traveling to Europe in order to avoid jet lag, the fact of why it is easier to travel west than east is detailed, and so is the therapeutic effect of this drug and the even better method of light provision in adjusting to different cycle needs.
The penultimate chapter provides some cautionary tales of mishaps when circadian needs are disregarded in our complex society. Precise information on the Chernobyl disaster and many other accidents are provided that can be traced directly to the disregard of physiological needs. Suggestions are made for "chronopharmacology," and eventually the book concludes with a "forward" look; what might be experimentally explored in the future and how this can affect our sociological behaviors.
This is the first comprehensive text on chronobiology and an absolutely fascinating read that should find a wide audience. We cannot escape the time constraints, as "the rotating features of Earth have influenced the evolution of rhythmicity in all living organisms."
Department of Pathology UCSD Medical Center San Diego, CA 92103
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