Table Of ContentWenner-Gren International Series
Vol. 60 Neuro-immunology of fever ed. T. Bartfai and D. Ottoson
Vol. 61 Functional organisation of the human visual cortex
ed. B. Gulyas, D. Ottoson and P. E. Roland
New in 1993
Light and biological rhythms in man ed. L Wetterberg
Trophic regulation of the basal ganglia ed. K. Fuxe et al.
Light and Biological
Rhythms in Man
Edited by
L. WETTERBERG
Karolinska Institute, Stockholm, Sweden
PERGAMON PRESS
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Copyright © 1993 Pergamon Press Ltd
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First edition 1993
Library of Congress Cataloging in Publication Data
New data to be supplied
ISBN 0-08-0422799
Printed in Great Britain by
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Preface
THE OBJECTIVE of this book is to summarize the knowledge of light as a
regulator of biological rhythms in man in relation to health and disease.
The first scientific meeting on biological rhythms in Sweden was held in
1937 in the small spa of Ronneby in the south of Sweden. About twenty
scientists who called themselves "Rhythms enthusiasts" gathered and
established a Society for Biological Rhythm Research. The second meeting
on biological rhythms in Sweden was held in 1955 in Stockholm, still with
a small group of scientists.
The presentations published in this book update what has happened
during the last four decades and focus in particular on how light is
influencing biological rhythms. In 1959 Aaron Lerner and coworkers
discovered the time keeping substance melatonin. In one chapter in this
book Lerner recounts the history of his efforts for four years to find the
melanin tonizing hormone (melatonin) which blanched frog skin, until
they found the substance and it could be said "This is it!". From there on
many speculations about the mediator of biological rhythm regulation
have become scientifically testable hypotheses. The results based on
Lerner's work have led to solid data on which much of modern biological
rhythm research is based.
That Aaron Lerner's historical aspects are included in this volume, as
well as all the other presentations will we hope benefit younger generations
of students and scientists for whom the research frontiers of today have a
strong bearing on the clinical practice of tomorrow and well beyond the
year 2000.
In different ways research is confronted with the fact that many of the
fundamental rhythm processes are not easily observable and must many
times be reconstructed from preliminary data. An interesting model to
explain the origin of biological rhythms is the one of Erik Odeblad from
University of Urnea, Sweden, who has proposed that it is based on the
presence of collective vibrations (phonons) in loop-shaped molecules or
molecular aggregates. Vibrational waves along a closed loop will give rise
to self-interference as the basis for rhythms. Further experiments to
measure phonons in tissues and organs are called for to test this
hypothesis.
V
vi Preface
As illustrated in this book, interfacing disciplines progress steadily
through experimentation, observation and theoretical interpretation, each
one helping the advances of the other. The biological rhythms covered in
this book range from short (infradian) and about 24-hour rhythms
(circadian) to longer rhythms (ultradian) present in all mammalian
species.
During the last decade it has become clear that humans also are in many
ways influenced by biological rhythms. Time structures are present on
several levels from population, individuals, organs (e.g. brain and heart) to
tissues, cells and subcellular organization. An introductory chapter
identifies the genetic machinery, including the light influenced proteins,
which governs the clocks that regulate us all.
The new findings about the effect of light on biological rhythms has
already lead to therapeutic trials in different conditions. The use of light to
regulate menstrual cyclicity may have clinical value for rhythm contracep-
tive methods and for treatment of infertility. The further studies of the
effect of light on the menstrual cycle may lead to new views of reproductive
endocrinology. In some chapters, specialists in light perception and light
reception have presented data on light treatment as an antidepressant in
seasonal affective disorder. It is clear that clinical testing is needed to
determine the optimal intensities, the timing and duration of light
treatment for producing beneficial effects.
In the report of placebo-controlled studies it is stated that it will require
further studies to establish how light treatment compares with placebo.
Such work is also important to help understand the mechanisms and
etiology of depression and other conditions.
To understand the rhythm regulating effects of light it is necessary to
examine the ocular mechanisms which mediate the photic effect through
the eye. When light reaches the retina, there are individual differences in
the sensitivity of the photoreceptivity and the ability of the melatonin
rhythm generating system to integrate photic stimuli, temporally.
The overall aim in the present volume is to provide a basis, both for
scientific as well as clinical perspectives to establish the specific modes and
measures which mediate therapeutic and physiologically beneficial effects
of light as a regulator of biological rhythms.
I am truly indebted to all of the contributors to this volume and very
grateful for the support and help of David Ottoson and Johan Beck-Friis.
The generous financial contribution of the Wenner-Gren Center Founda-
tion and the Swedish Medical Research Council is acknowledged.
Stockholm, 1993
LENNART WETTERBERG
1
Biological Rhythms: From Gene
Expression to Behavior*
JOSEPH S. TAKAHASHI
NSF Center for Biological Timing, Department of Neurobiology and
Physiology, Northwestern University, Evanston, IL 60208-3520, USA
Abstract
Circadian rhythms regulate the function of living systems at virtually every level of
organization. In the last decade, our understanding of the cellular and molecular processes
involved in the generation and regulation of circadian rhythms has advanced considerably.
New model systems for studying circadian oscillators have been developed, a potential
regulatory role for cellular immediate-early genes in circadian behavior has been discovered,
and critical periods of macromolecular synthesis for progression of the circadian clock
through its cycle have been defined. These findings are of particular interest because
independent approaches suggest that an important role for macromolecular synthesis exists
at all levels of the circadian system.
Introduction
Circadian rhythms regulate the behavior, physiology and b3io,ch1e5m05is,try3 o8f
most living systems: from cyanobacterium to man. ' Among
animals, much is known about the physiology of circadian rhythms, and in
all cases, circadian control is exerted by structure4s 2th4at 5,co251n5t9ain circadian
pacemakers within the central nervous system. ' ' ' On the basis of
a wide variety of evidence, the mechanism of the circadian clock app5ea51rs52 4to
be cell autonomous and to involve periodic gene expression. ' ' In
addition, signal transduction pathways into the clock mechanism are
present for conveying environmental information for entrainment of the
clock. Furthermore, the clock mechanism has diverse output pathways for
exerting circadian control at all levels of organismal biology. A number of
generalizations can be made about circadian biology. Circadian rhythms
are a property of all eukaryotic and some prokaryotic organisms and are
entrained primarily by environmental cycles of light and temperature.
Circadian rhythms are genetically determined and single-gene clock
* This paper is dedicated to Dr Aaron B. Lerner for his seminal work on melatonin.
3
4 Light and Biological Rhythms in Man
mutants have been found in six organisms including mammals. Circadian
oscillations are remarkably precise and can have a variation in cycle length
of less than one part in a thousand. The period length of the oscillation is
temperature-compensated and usually varies less than 20% for each 10°C
change in temperature (Q = 0.8-1.2). Finally, the biochemical ma-
1Q
chinery responsible for generating circadian rhythms can be expressed at
the level of individual cells. Thus, circadian rhythmicity is a fundamental
organizing feature of virtually all organisms. The properties of these
rhythms are unique and widely conserved among living systems.
This chapter will be organized in two parts. First, a brief review of
vertebrate circadian organization will be presented. Second, a summary of
our own work on photic entrainment and regulation of immediate early
genes in mammals will follow.
Components of circadian systems
All circadian systems contain at least three elements: (1) an input pathway
or set of input pathways that convey environmental information to the
circadian pacemaker for entrainment; (2) a circadian pacemaker that
generates the oscillation; and (3) an output pathway or set of output 58
pathways by which the pacemaker regulates its various output rhythms.
In all systems, a photic entrainment pathway is present as an input. It is
already clear from the diversity of photopigments and phototransduction
pathways th3a8t photic entrainment pathways differ markedly in different
organisms. At the receptor level, the diversity spans the spectrum from
phytochrome in plants to members of the rhodopsin family in animals.
There appears to be comparable diversity at the second messenger level in
photic signal transduction pathways. At the output level, diversity is even
more extreme. Again, this type of regulation spans the clock control of
photosynthesis in plants to endo5c1rine and behavioral rhythms in animals.
As I have argued previously, the input and output pathways of the
circadian clock within each organism appear to be specific to each system.
Despite these differences in the coupling pathways (inputs and outputs) of
the circadian clock, the core mechanism of the pacemaker appears to be
fundamentally similar in all organisms. Whether these similarities in
pacemaker mechanisms will ultimately be found to be functionally
analogous or phylogenetically homologous remains to be seen.
Physiological organization of vertebrate circadian
systems
Circadian pacemakers, which control the behavior and physiology of
animals, 4ha5ve5, 5b4ee8n localized as discrete structures within the nervous
system. ' At the physiological level, both "oscillator" and "pace-
maker" function have been defined. A "circadian oscillator" is a structure
Biological Rhythms: From Gene Expression to Behavior 5
that expresses a self-sustained oscillation under constant conditions (the
absolute minimum number of cycles is two). Circadian oscillators have
been localized by isolating the tissue in question in vitro and then
demonstrating the persistence of circadian oscillations in the isolated
tissue under constant conditions. In vertebrates, three diencephalic
structures have been shown to con5t5ain circadian oscillators, the pineal
gland of birds, reptiles and fi2sh24,9 the hypothalamic suprachiasmatic
nucleus4 37(SCN) of mammals, ' and the retinas of amphibians and
birds. ' A "circadian pacemaker" is a circadian oscillator that has been
shown to drive and therefore control some overt rhythmic process such as
locomotor behavior. Pacemaker function has been experimentally demon-
strated by transplanting the structure in question and then showing that
the phase or period of the recipient rhythm is regulated by the transplant.
This result has been demonstrated in vertebrates for the pineal gland of
sparrows and the SCN of hamsters, and in inverteAb2r>atAe5s for the optic lobes
of cockroaches and the brain of Drosophila.
Although an ocular-SCN-pineal axis underlies vertebrate circadian
organization, it is difficult to make simple generalizations at the
physiological level. The clearest division is a mammalian versus non-
mammalian dichotomy. In mammals, the organization is the simplest. The
dominant circadian pacemaker is located in the SCN, the photoreceptors
for entrainment are exclusively retinal, and output 24pathways such as the
pineal rhythm of melatonin are well defined. I3n 455non-mammalian
vertebrates, the organization is more complex; ' and, multiple
oscillators and photoreceptors are involved. The pineal gland, the SCN
and the eyes can each play a dominant role in circadian behavior of birds
depending on the species. For example, in passerine birds, such as the
house sparrow, the pineal gland plays a dominant pacemaker role;
whereas, in gallinaceous birds, such as chickens and quail, the pineal gland
is not essential. The avian SCN appears to be necessary in all species
examined, but its role as a pacemaker has not been determined. Finally, in 60
Japanese quail, the eyes play a dominant role in circadian organization.
In addition to the multiplicity of oscillatory centers, multiple photorecep-
tors for6 1entrainment are located in the retina, the pineal gland and the
brain. In summary, non-mammalian vertebrates appear to have
distributed circadian oscillators with local photoreceptive input; whereas,
mammals appear to have retained only a subset of these components.
The mammalian suprachiasmatic nucleus
A wealth of experimental evidence strongly argues that the hypothalamic
SCN is the 2sit2e4 o49f 45a8 circadian pacemaker that drives overt rhythms in
mammals. ' ' ' Six lines of evidence support this conclusion. First,
the SCN receives direct input from the retina through a specialized visual
6 Light and Biological Rhythms in Man
pathway, the retinohypothalamic tract, which is required for entrainment
to light cycles. Second, a wide variety of circadian rhythms in rodents are
disrupted by SCN lesions, ruling out the possibility of a highly specific,
limited effect of lesions on a particular subsystem, for instance, locomotor
behavior. Third, the SCN expresses circadian rhythms of multi-unit
electrical activity that persist after neural isolation in vivo. Fourth, SCN
expiants continue to express circadian rhythms of single-unit electrical
activity, vasopressin release and metabolic activity in vitro. Fifth, circadian
rhythmicity can be restored to arrhythmic SCN-lesioned animals by
transplantation of fetal tissue containing SCN cells. Sixth, transplantation
of SCN tissue derived from Tau mutant hamsters, which express short
period rhythms, demonstrates that the genotype of the donor SCN
determines the period of the restored rhythm. Taken together, these results
demonstrate that the SCN plays a dominant role in the generation of
circadian rhythms in mammals.
Functional properties of photic entrainment in
mammals
Photic entrainment in mammals is mediated by retinal p29hotoreceptors
that project to the SCN via the retinohypothalamic tract. We have used
light-induced phase shifts of the circadian rhythm of wheel-running
activity to measure the photic sensitivity of the circadian system of the
golden hamster. Previously we showed that the spectral sensitivity
function for phase-shifting m5a3tches an opsin-based photopigment with a
peak (A ) around 500 nm. Although the peak sensitivity is similar to
m a x
that of rhodopsin, two features of this photoreceptive system are unusual:
the threshold of the response is high, especially for a rod-dominated retina
like that of the hamster, and the reciprocal relationsh3i3p between intensity
and duration holds for extremely long durations. Figure 1 shows the
phase-shifting response to 300 sec light pulses at circadian time (CT) 19.
The phase-shifting response increases with light intensity and can be fit
with a four parameter logistic function. The sensitivity to stimulus duration
was assessed by measuring the magnitude of phase-shift responses to
photic stimuli of different irradiance and duration (Figure 2). The hamster
circadian system is more sensitive to the irradiance of longer duration
stimuli than to that of briefer stimuli. The system is maximally sensitive to
the irradiance of stimuli of 300 sec and longer in duration (Figure 3A). As
shown previously the threshold for photic stimulation of the hamster
circadian pacemaker is high. The threshold irradiance (the maximum
irradiance necessa1r1y to induce -2statisti1cally significant responses) is
approximately 10 photons cm sec" for optimal stimulus durations.
This th2reshold is equivalent to a luminance at the cornea of about 0.1
cd-m~ . We also measured the sensitivity of this visual pathway to the
Biological Rhythms: From Gene Expression to Behavior 1
y/-
' — — • — • — • — . — • — • — · — • — -J
Dark 8 9 10 11 12 13 14 15 16 17
Irradiance (log photons · cm~~2 . —s 1 )
FIG. 1. Magnitude of phase shift of hamster activity rhythm in response to 300 sec
503 nm light pulses of different irradiance at circadian time 19 (C3T319). The points
represent the mean±SEM. The continuous line is a modified Naka-Rushton
function fitted to the data. (From Nelson and Takahashi, copyright by J.
Physiol. (Lond.).)
Dark 9 10 11 12 13 14 15
Log (irradiance)
FIG. 2. Magnitude of phase shift of hamster activity rhythm in response to 503 nm
light pulses of varying durations and irradiances at CT19. Open circles are 3,600
sec; closed circles are 300 sec; op33en triangles are 30 sec; and closed triangles are 3
sec stimuli. Curves are best fit modified Naka-Rushton functions. (From Nelson
and Takahashi, copyright by J. Physiol. (Lond.).)
total number of photons in a stimulus (Figure 3B). Surprisingly, the system
is maximally sensitive to photic stimuli between 30 and 3,600 sec in
duration. The maximum quantum efficiency of photic integration occurs
in 300 sec stimuli.
To summarize, the photic threshold for entrainment, even under
optimal conditions, is relatively insensitive and corresponds to thresholds
reported for cone photoreceptors. In addition, the system can integrate
light over very long durations. From a functional perspective, these
characteristics are clearly adaptive. The threshold is just above the level of
full moonlight and thus entrainment would not be disrupted by this
inappropriate light source. Furthermore, the optimum for long duration
pulses would also render the system insensitive to very intense but brief
