Jürgen Aschoff
Encyclopedia
Jürgen Walther Ludwig Aschoff (January 25, 1913 - October 12, 1998) was a German
physician
, biologist
and behavioral physiologist. Together with Erwin Bünning
and Colin Pittendrigh
, he is considered to be a co-founder of the field of chronobiology
.
(known for discovering the Aschoff-Tawara or atrioventricular node
) and his wife Clara. He grew up in the liberal but morally strict world of Prussian academia. After the Abitur
at a humanistic high school he - according to his own statement "lacking a specific interest" - studied medicine at the University of Bonn
, where he joined the Burschenschaft Alemannia Bonn. Aschoff’s scientific career began in 1938, when he moved to the University of Göttingen to study thermoregulation
physiology
with Hermann Rein. In 1944, he received the venia legendi. He then became a professor at the University of Gottigen in 1949.
In 1952, his mentor, Hermann Rein, was appointed director of the Max Planck Institute for Medical Research
in Heidelberg
. Rein brought Aschoff to the Institute as a collaborator to study circadian rhythms in humans, birds, and mice. Aschoff then moved to the Max Planck Institute for Behavioral Physiology
in Andechs
to work with Gustav Kramer, who showed time-compensated sun-compass navigation in birds, and Erich von Holst
, who studied physiological oscillators. From 1967 to 1979, he was a director at the Max Planck Institute for Behavioral Physiology and an extraordinary professor in Munich
. Aschoff was a scientific member and a member of the Kollegiums of the Max Planck Institute for Behavior Physiology, as well as senator of the Max Planck Society
from 1972 to 1976.
Aschoff was known as an excellent lecturer with a booming voice, and he took a special interest in creating a scientific community and encouraging young scientists. After his retirement in 1983 and return to Freiburg, Aschoff continued his scientific work in the form of further publications. Only the death of his wife Hilde broke his unusual vitality. Jürgen Aschoff died 10 months after his wife in 1998, after a short illness at the age of 85 years.
in many different organisms such as rats, mice, birds, macaque
s, monkeys, and humans. His early research focused on understanding the properties of circadian rhythms and how these rhythms can change in response to stimuli. His later work was more applicable to pathologies, such as psychiatric disorders and dangers of shift work
schedules, which can result from manipulating specific Zeitgeber
s. Aschoff's work in the field of chronobiology introduced the idea that shifting one's light-dark cycle can result in harmful effects, such as correlations with mental illness.
Aschoff also applied these methods to experiments with human circadian rhythms by building an underground "bunker" to isolate human subjects from any external environmental cues. Subjects placed in this bunker were allowed to turn lights on or off according to their own internal rhythms. After over twenty years of tracking sleep-wake cycles, body temperature, urine output, and other physiological and behavioral outputs, Aschoff and his collaborator Rütger Wever
concluded that humans have endogenous circadian oscillators. This discovery has become the foundation for our understanding of many medical problems such as aging
, sleep disorder
s, and jet lag
.
In 1960, Aschoff coined the term Zeitgeber (from German for "time giver" or "synchronizer") to refer to external, environmental cues that synchronize an endogenous oscillator to the environmental cycle. To investigate the properties of natural endogenous oscillators, Aschoff exposed organisms to constant conditions without Zeitgeber cues (either constant light or constant darkness). The observations from this paper were formulated into the fundamental rules of biological clocks.
Aschoff's rule is related to the model of parametric entrainment, which assumes continuous phase changes. Aschoff and Pittendrigh approached the field with different models of how oscillators entrain, which resulted in different predictive models. Aschoff's parametric model states that entrainment occurs through gradual changes in the clock that adapt to a new light-dark cycle. Although this is no longer recognized as the correct model in the field, Serge Daan
suggested in 1998 that Aschoff made qualitative contributions that provide valuable alternatives to inconsistencies in the current field.
Aschoff also found that different circadian outputs such as body temperature and locomotor activity
can be either internally synchronized or desynchronized depending on the strength of the Zeitgeber. In constant darkness, rectal temperature and sleep onset and duration became desynchronized in some subjects, and the rectal temperature at the time of sleep onset was correlated to the duration of the bout of sleep. He hypothesized that internal desynchronization, the phase differences resulting from period differences between two circadian output processes, could be related to many psychiatric disorders.
Some of Aschoff's later work also integrated his initial interest in thermoregulation with his work on circadian rhythm. He found a circadian rhythm in thermal conductance, a measurement of heat transfer from the body. Minimal conductance in mammals and birds oscillates with circadian phase, with a wide range of conductance values. This allows animals to release heat during their activity period, when they have higher basal metabolism, as well as conserve heat during their rest period, when they have lower basal metabolism. In birds, the circadian rhythm in conductance results mostly from circadian rates of evaporative heat loss. In mammals, the conductance oscillates with circadian rhythms in the body's heat resistance and blood flow rate.
Following up on his temperature studies, he found that a mammalian species can entrain to a temperature cycle, but that temperature is a weak Zeitgeber compared to a light-dark cycle.
Aschoff described masking signals as inputs that circumvent the pacemaker but nevertheless lead to modulation of a circadian behavior that is also controlled by the pacemaker. Parametric entrainment is entrainment that does not result from an instant change in phase, as governed by a Phase Response Curve
, as in the case of masking signals. The term Aschoff used for this phenomenon is “arousal” due to non-photic zeitgebers. Data from experimental assays show a relationship between masking effects and phase, leading to a “demasking” effect whereby animals arrhythmic in constant conditions have free-running periods in high frequency light-dark cycles. Aschoff concluded that the oscillator or circadian clock “integrates” over the intensity of light to which it has been exposed, and then responds with a change in the period of activity, as seen in greenfinches, chaffinches, hamsters, and siskins. Aschoff concluded, however, that non-parametric effects, as opposed to parametric effects, are the principal source of entrainment.
2) An increase in strength of the zeitgeber should increase as sunset duration increases.
Although Aschoff’s collaboration with Gustav Kramer was never fully realized due to the latter’s sudden death, Aschoff continued to use birds as model organisms and work with ornithologists.
Germans
The Germans are a Germanic ethnic group native to Central Europe. The English term Germans has referred to the German-speaking population of the Holy Roman Empire since the Late Middle Ages....
physician
Physician
A physician is a health care provider who practices the profession of medicine, which is concerned with promoting, maintaining or restoring human health through the study, diagnosis, and treatment of disease, injury and other physical and mental impairments...
, biologist
Biologist
A biologist is a scientist devoted to and producing results in biology through the study of life. Typically biologists study organisms and their relationship to their environment. Biologists involved in basic research attempt to discover underlying mechanisms that govern how organisms work...
and behavioral physiologist. Together with Erwin Bünning
Erwin Bünning
Dr Erwin Bünning was a German biologist. His pioneering research in botany and plant physiology resulted in several contributions in phototropism, phototaxis, differentiation, growth substances and even Tropical Forests...
and Colin Pittendrigh
Colin Pittendrigh
Colin Pittendrigh was a US-American biologist of English parentage. He is a co-founder of modern chronobiology along with Jürgen Aschoff and Erwin Bünning.-Life:...
, he is considered to be a co-founder of the field of chronobiology
Chronobiology
Chronobiology is a field of biology that examines periodic phenomena in living organisms and their adaptation to solar- and lunar-related rhythms. These cycles are known as biological rhythms. Chronobiology comes from the ancient Greek χρόνος , and biology, which pertains to the study, or science,...
.
Life
Aschoff was born in Freiburg Im Breisgau as the fifth child of the pathologist Ludwig AschoffLudwig Aschoff
Karl Albert Ludwig Aschoff was a German physician and pathologist. He is considered to be one of the most influential pathologists of the early 20th century and is regarded as the most important German pathologist after Rudolf Virchow.Aschoff was born in Berlin, Prussia...
(known for discovering the Aschoff-Tawara or atrioventricular node
Atrioventricular node
The atrioventricular node is a part of the electrical control system of the heart that coordinates heart rate. It electrically connects atrial and ventricular chambers...
) and his wife Clara. He grew up in the liberal but morally strict world of Prussian academia. After the Abitur
Abitur
Abitur is a designation used in Germany, Finland and Estonia for final exams that pupils take at the end of their secondary education, usually after 12 or 13 years of schooling, see also for Germany Abitur after twelve years.The Zeugnis der Allgemeinen Hochschulreife, often referred to as...
at a humanistic high school he - according to his own statement "lacking a specific interest" - studied medicine at the University of Bonn
University of Bonn
The University of Bonn is a public research university located in Bonn, Germany. Founded in its present form in 1818, as the linear successor of earlier academic institutions, the University of Bonn is today one of the leading universities in Germany. The University of Bonn offers a large number...
, where he joined the Burschenschaft Alemannia Bonn. Aschoff’s scientific career began in 1938, when he moved to the University of Göttingen to study thermoregulation
Thermoregulation
Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different...
physiology
Physiology
Physiology is the science of the function of living systems. This includes how organisms, organ systems, organs, cells, and bio-molecules carry out the chemical or physical functions that exist in a living system. The highest honor awarded in physiology is the Nobel Prize in Physiology or...
with Hermann Rein. In 1944, he received the venia legendi. He then became a professor at the University of Gottigen in 1949.
In 1952, his mentor, Hermann Rein, was appointed director of the Max Planck Institute for Medical Research
Max Planck Institute for Medical Research
The Max Planck Institute for Medical Research in Heidelberg, Germany, is a facility of the Max Planck Society for basic medical research. Since its foundation, six Nobel Prize laureates worked at the Institute: Otto Fritz Meyerhof , Richard Kuhn , Walther Bothe , André Michel Lwoff , Rudolf...
in Heidelberg
Heidelberg
-Early history:Between 600,000 and 200,000 years ago, "Heidelberg Man" died at nearby Mauer. His jaw bone was discovered in 1907; with scientific dating, his remains were determined to be the earliest evidence of human life in Europe. In the 5th century BC, a Celtic fortress of refuge and place of...
. Rein brought Aschoff to the Institute as a collaborator to study circadian rhythms in humans, birds, and mice. Aschoff then moved to the Max Planck Institute for Behavioral Physiology
Max Planck Institute for Behavioral Physiology
The former Max Planck Institute for Behavioral Physiology was located in Seewiesen, Bavaria, Germany. It was one of 80 institutes in the Max Planck Society ....
in Andechs
Andechs
The Benedictine abbey of Andechs is a place of pilgrimage on a hill east of the Ammersee in the Landkreis of Starnberg in Germany, in the municipality Andechs. Andechs Abbey is famed for its flamboyant Baroque church and its brewery...
to work with Gustav Kramer, who showed time-compensated sun-compass navigation in birds, and Erich von Holst
Erich von Holst
Erich von Holst , was a German behavioral physiologist who was a native of Riga, and was related to historian Hermann Eduard von Holst...
, who studied physiological oscillators. From 1967 to 1979, he was a director at the Max Planck Institute for Behavioral Physiology and an extraordinary professor in Munich
Munich
Munich The city's motto is "" . Before 2006, it was "Weltstadt mit Herz" . Its native name, , is derived from the Old High German Munichen, meaning "by the monks' place". The city's name derives from the monks of the Benedictine order who founded the city; hence the monk depicted on the city's coat...
. Aschoff was a scientific member and a member of the Kollegiums of the Max Planck Institute for Behavior Physiology, as well as senator of the Max Planck Society
Max Planck Society
The Max Planck Society for the Advancement of Science is a formally independent non-governmental and non-profit association of German research institutes publicly funded by the federal and the 16 state governments of Germany....
from 1972 to 1976.
Aschoff was known as an excellent lecturer with a booming voice, and he took a special interest in creating a scientific community and encouraging young scientists. After his retirement in 1983 and return to Freiburg, Aschoff continued his scientific work in the form of further publications. Only the death of his wife Hilde broke his unusual vitality. Jürgen Aschoff died 10 months after his wife in 1998, after a short illness at the age of 85 years.
Work
Aschoff provided a strong foundation for the field of chronobiology through his research on circadian rhythms and entrainmentEntrainment (chronobiology)
Entrainment, within the study of chronobiology, occurs when rhythmic physiological or behavioral events match their period and phase to that of an environmental oscillation. A common example is the entrainment of circadian rhythms to the daily light–dark cycle, which ultimately is determined by...
in many different organisms such as rats, mice, birds, macaque
Macaque
The macaques constitute a genus of Old World monkeys of the subfamily Cercopithecinae. - Description :Aside from humans , the macaques are the most widespread primate genus, ranging from Japan to Afghanistan and, in the case of the barbary macaque, to North Africa...
s, monkeys, and humans. His early research focused on understanding the properties of circadian rhythms and how these rhythms can change in response to stimuli. His later work was more applicable to pathologies, such as psychiatric disorders and dangers of shift work
Shift work
Shift work is an employment practice designed to make use of the 24 hours of the clock. The term "shift work" includes both long-term night shifts and work schedules in which employees change or rotate shifts....
schedules, which can result from manipulating specific Zeitgeber
Zeitgeber
Zeitgeber is any exogenous cue that synchronizes an organism's endogenous time-keeping system to the earth's 24-hour light/dark cycle. The strongest zeitgeber, for both plants and animals, is light...
s. Aschoff's work in the field of chronobiology introduced the idea that shifting one's light-dark cycle can result in harmful effects, such as correlations with mental illness.
Early work
Aschoff began his research on the physiology of thermoregulation by self-experimentation. He discovered that there was a 24-hour rhythm of variation in body temperature. After these experiments, he began investigating the basic mechanisms of circadian rhythm. In the 1950s, he met and began to collaborate with Erwin Bünning and Colin Pittendrigh. Aschoff began further experimentation studying the circadian rhythms of birds and mice under constant conditions. His results led to the conclusion that circadian oscillations of biological processes were innate and did not require prior exposure to a 24-hour day to be expressed.Aschoff also applied these methods to experiments with human circadian rhythms by building an underground "bunker" to isolate human subjects from any external environmental cues. Subjects placed in this bunker were allowed to turn lights on or off according to their own internal rhythms. After over twenty years of tracking sleep-wake cycles, body temperature, urine output, and other physiological and behavioral outputs, Aschoff and his collaborator Rütger Wever
Rütger Wever
Rütger Wever is a German scientist, known for his significant contributions to the field of Chronobiology, including some of the first experiments on humans in time isolated environments.-Time isolation experiments:...
concluded that humans have endogenous circadian oscillators. This discovery has become the foundation for our understanding of many medical problems such as aging
Ageing
Ageing or aging is the accumulation of changes in a person over time. Ageing in humans refers to a multidimensional process of physical, psychological, and social change. Some dimensions of ageing grow and expand over time, while others decline...
, sleep disorder
Sleep disorder
A sleep disorder, or somnipathy, is a medical disorder of the sleep patterns of a person or animal. Some sleep disorders are serious enough to interfere with normal physical, mental and emotional functioning...
s, and jet lag
Jet lag
Jet lag, medically referred to as desynchronosis, is a physiological condition which results from alterations to the body's circadian rhythms; it is classified as one of the circadian rhythm sleep disorders...
.
In 1960, Aschoff coined the term Zeitgeber (from German for "time giver" or "synchronizer") to refer to external, environmental cues that synchronize an endogenous oscillator to the environmental cycle. To investigate the properties of natural endogenous oscillators, Aschoff exposed organisms to constant conditions without Zeitgeber cues (either constant light or constant darkness). The observations from this paper were formulated into the fundamental rules of biological clocks.
Aschoff's Rule
From the experiments communicated in 1960, Aschoff noted that under constant light conditions, the activity phase shortens in nocturnal organisms and lengthens in diurnal organisms. These trends were termed alpha compression and alpha expansion, respectively. In tribute to his mentor, Pittendrigh called this observation "Aschoff's Rule" in a 1960 publication, and the designation remains today.Aschoff's rule is related to the model of parametric entrainment, which assumes continuous phase changes. Aschoff and Pittendrigh approached the field with different models of how oscillators entrain, which resulted in different predictive models. Aschoff's parametric model states that entrainment occurs through gradual changes in the clock that adapt to a new light-dark cycle. Although this is no longer recognized as the correct model in the field, Serge Daan
Serge Daan
Serge Daan is a Dutch scientist, known for his significant contributions to the field of Chronobiology.-Early life and education:Serge Daan was born in a wind mill, grew up in the Dutch countryside, and went to high school in Deventer...
suggested in 1998 that Aschoff made qualitative contributions that provide valuable alternatives to inconsistencies in the current field.
Later work
Much of Aschoff's later work involved tests on human subjects. He found that the absence of a light-dark cycle does not prevent humans from entrainment. On the contrary, he concluded that light is a weak Zeitgeber for humans, because people kept on a 24-hour light-dark cycle tended to free-run with periods greater than 24 hours. Rather, knowing the time of day from social cues, such as regular meal times, is sufficient for entrainment.Aschoff also found that different circadian outputs such as body temperature and locomotor activity
Locomotor activity
Locomotor activity refers to the movement from place to place. In psychopharmacology, locomotor activity of lab animals is often monitored to assess the behavioural effects of these drugs. Locomotor activity is useful and less robust than most behavioural tests such as operant conditioning and...
can be either internally synchronized or desynchronized depending on the strength of the Zeitgeber. In constant darkness, rectal temperature and sleep onset and duration became desynchronized in some subjects, and the rectal temperature at the time of sleep onset was correlated to the duration of the bout of sleep. He hypothesized that internal desynchronization, the phase differences resulting from period differences between two circadian output processes, could be related to many psychiatric disorders.
Some of Aschoff's later work also integrated his initial interest in thermoregulation with his work on circadian rhythm. He found a circadian rhythm in thermal conductance, a measurement of heat transfer from the body. Minimal conductance in mammals and birds oscillates with circadian phase, with a wide range of conductance values. This allows animals to release heat during their activity period, when they have higher basal metabolism, as well as conserve heat during their rest period, when they have lower basal metabolism. In birds, the circadian rhythm in conductance results mostly from circadian rates of evaporative heat loss. In mammals, the conductance oscillates with circadian rhythms in the body's heat resistance and blood flow rate.
Following up on his temperature studies, he found that a mammalian species can entrain to a temperature cycle, but that temperature is a weak Zeitgeber compared to a light-dark cycle.
Aschoff described masking signals as inputs that circumvent the pacemaker but nevertheless lead to modulation of a circadian behavior that is also controlled by the pacemaker. Parametric entrainment is entrainment that does not result from an instant change in phase, as governed by a Phase Response Curve
Phase response curve
A phase response curve illustrates the transient change in the cycle period of an oscillation induced by a perturbation as a function of the phase at which it is received...
, as in the case of masking signals. The term Aschoff used for this phenomenon is “arousal” due to non-photic zeitgebers. Data from experimental assays show a relationship between masking effects and phase, leading to a “demasking” effect whereby animals arrhythmic in constant conditions have free-running periods in high frequency light-dark cycles. Aschoff concluded that the oscillator or circadian clock “integrates” over the intensity of light to which it has been exposed, and then responds with a change in the period of activity, as seen in greenfinches, chaffinches, hamsters, and siskins. Aschoff concluded, however, that non-parametric effects, as opposed to parametric effects, are the principal source of entrainment.
Aschoff-Wever Model
1) An increase in the duration of sunset advances the phase of an organism for nocturnal and diurnal animals.2) An increase in strength of the zeitgeber should increase as sunset duration increases.
Influence on other researchers
Aschoff has published articles with both Pittendrigh and Serge Daan, the latter also a pivotal researcher in chronobiology. In his recent work, Daan has attempted to reconcile the idea of parametric entrainment to light proposed by Aschoff with the non-parametric model of entrainment proposed by Pittendrigh, and results from a 2008 paper from Daan's lab lend further evidence to Aschoff's model of parametric entrainment.Although Aschoff’s collaboration with Gustav Kramer was never fully realized due to the latter’s sudden death, Aschoff continued to use birds as model organisms and work with ornithologists.
Aschoff's Rule (prize)
At a dinner held in Aschoff's honor at the 1991 Gordon Conference on Chronobiology, Professor Till Roenneberg initiated the annual giving of the Aschoff's Rule prize to scientists who have advanced the field of chronobiology by presenting a plaque with a ruler on it to Professor Maroli K. Chandrashekera. Recipients choose the winner the following year and must follow two guidelines:- The successor should be a chronobiologist working in a country different to the one of the current holder of the prize.
- The successor should be working with an organism different to the one of the current holder of the prize.
Selected publications
- Exogenous and Endogenous Components in Circadian Rhythms" (1960),
- Beginn und Ende der täglichen Aktivität freilebender Vögel“ (mit R. Wever, 1962),
- Circadian Clocks" (1965), "Desynchronization and Resynchronization of Human Circadian Rhythm“ (1969),
- Aschoff, Jürgen. (1965) Circadian Rhythms in Man. Science. 148: 1427-1432.