Monday, February 28, 2005

ClockNews #28: Asthma, Constant Light and Insomnia

Time Allergy and Asthma Medications for Best Effect

Allergy and asthma sufferers can maximize the benefit of their
medications by taking advantage of their bodies' natural circadian rhythms,
according to Richard Martin, M.D., Professor of Medicine at National Jewish
Medical and Research Center.

Body clocks response to constant light

Constant light has long been understood to disrupt our internal
clocks, resulting in problems like jet lag and health problems in extended-shift
workers. A study led by Vanderbilt researcher Douglas McMahon reveals that
although the clocks of individuals exposed to constant light may get out of
synch, they keep ticking.
synchronization of our internal biological clocks has important health
consequences. For example, babies held in the neonatal intensive care unit under
constant dim light can show lower weight gain than those on a more natural light
cycle. Repeated jet lag can also have adverse health effects.

Habits may cause insomnia

"The majority of people say they always have slept fine until
recently. Almost all kids sleep pretty well and wake up annoyingly perky and go
to bed and get up when mom and dad tell them.It’s only later on that people need
to use medications and they have sleep disturbances," said McNally.

Tuesday, February 22, 2005

New Blog Carnival Showcase Extravaganza

Circadiana has been showcased in the brand new issue of the New Blog Carnival Showcase Extravaganza No. 2

Sunday, February 20, 2005

ClockQuotes #3

The only reason for time is so that everything doesn't happen at once.
Albert Einstein, 1879 - 1955

Saturday, February 19, 2005

ClockNews #27: A Venerable Cornucopia Of Arcane Circadiana

Biological clock may shut down long-term memory at night

Scientists have known for a while that the brain's biological (or circadian) clock influences natural body cycles, such as sleep and wakefulness, metabolic rate and body temperature. New research from Eskin suggests the circadian clock also may regulate the formation of memory at night. This new research focuses on "Circadian Modulation of Long-term Memory Formation" and "Long-term Regulation of Glutamate Uptake in Aplysia," with NIH funding to be disbursed over four years.

UH Professor receives $2.5 million in grants to continue learning, memory research

"There is a lot of research going on in memory," Eskin said. "How do we remember things given that we don't have a camera in our brain to record events? What changes take place in our brains that allow us to remember? These grants are about fundamental learning and memory and about modulation of memory."

Local college students win awards in academics from USA Today

Wat studied circadian rhythms while still a high school student and did breast cancer research at Cold Spring Harbor Laboratory in New York, where she met Watson.

Dark little secret

Imagine a scenario where you get up in the morning with absolutely no hunger. You don't eat.
As the day wears on, you drink a lot of coffee. You eat a light lunch or snack.
Come dinnertime you're ravenous. You eat dinner.
But then you snack after dinner almost continuously right up to the time you go to bed. Your choices may include candy, cookies, potato chips or ice cream.
After falling asleep, you wake up and are convinced you can't get back to sleep unless you eat something. You feel frantic. That's when you steal into the kitchen and eat peanut butter right out of the jar.
This is the pattern day after day for people with night eating syndrome.

Best Time Of Day

If you stop and think for a moment, you might be surprised at all you get done in a day. But you may not be doing it as efficiently as you could. There is real science behind when to eat breakfast and ask the boss for a raise. CBS 2's Alita Guillen tells you the best time of day. We're busy doing it all, but maybe we are doing it all at the wrong time.

New Effects Of Melatonin Revealed

In a recent study, researchers found that the melatonin hormone supplement that is available without a prescription has greater effects on the body than previously thought.
[I have data that are consistent with their data but not with their conclusions. Your curiosity will have to wait until my stuff is published - sorry]

Rods and cones... and these

The recent discovery of inner retinal photoreceptors in mammals and fish was a major surprise. Present in addition to the well known rods and cones, these receptors are thought to detect irradiance levels, and to be linked to the night-and-day regulation of the circadian system. Two new studies show that melanopsin, found almost exclusively in these 'ganglion-cell photoreceptors', is photosensitive. Qiu et al. turn mammalian kidney cells into functional photoreceptors by introducing melanopsin, and Melyan et al. do a similar trick in neuronal cells. These findings could have clinical applications, possibly allowing selective stimulation of cells in the brain and helping to restore sight lost due to retinal degeneration. A further study identifies a previously unknown retinal population of 'giant' melanopsin-expressing ganglion cells. They are photosensitive but are also activated by rods and cones, thereby merging the conventional 'image forming' pathway with the radiance-detecting pathway in primates.

Naturopathic medicine: Guidelines can help the sleep-deprived

I have been battling insomnia for years. I read your article on the ramifications of inadequate sleep and would really appreciate some non-drug sleep guidelines.

Lung function peaks during late afternoon

Researchers say lung function has a natural rhythm that peaks during late afternoon and bottoms out around midday. Ultimately, this information may help determine the best time of day to exercise or take certain drugs.

Morning Exercise May Make Sleep Easier

Older women who often have trouble sleeping may want to consider a little workout in the morning for a better rest at night.
Morning exercisers had fewer complaints about a bad night's sleep and those who stretched in the morning had somewhat better sleep, a new study found. Women who exercise in the evening, on the other hand, were more likely to be up at night.

Nurses as Shiftworkers: New Report Is First of Its Kind to Detail Key Labor, Economic, and Safety Issues, and Proposed Solutions

Despite projections that nursing is one of the top ten growth jobs for the next 15 years, our health care system is on the verge of an overwhelming nurse shortage and health care crisis. In fact, an estimated 50% of nurses will be at retirement age within 15 years, and new nurses aren't entering the field fast enough to stabilize the imminent mass departure. This and other issues are explored in depth in "Extended Hours Issues in Nursing: Exploring the Problems, Finding the Solutions," the new report from CIRCADIAN, a research and consulting firm specializing in reducing shiftwork operations' costs, risks, and liabilities.

2004 Grand Prize Winner

Dr. Tu obtained his Ph.D. in 2003 and moved to the University of Texas Southwestern Medical Center in Dallas, where he is a postdoctoral fellow in the laboratory of Dr. Steven L. McKnight with a fellowship from the Helen Hay Whitney Foundation. He is currently studying the metabolic cycles of yeast and hopes to apply what he learns to the study of circadian rhythms.

Electric Light-Breast Cancer Link Studied

Their theory is that prolonged periods of exposure to artificial light disrupt the body's circadian rhythms - the inner biological clocks honed over thousands of years of evolution to regulate behaviors such as sleep and wakefulness. They are looking into whether that disruption affects levels of hormones such as melatonin and the workings of cellular machinery, and whether it triggers breast cancer.

Some snooze, some lose
High-schoolers sleep more; others on buses earlier!localnews!education&s=1037645509111

With a later school-start time, high-school students in the Winston-Salem/Forsyth County school system reported sleeping about 34 more minutes every night, doing more homework and falling asleep in class less frequently, according to a survey released this week.
"Those are really positive results," Superintendent Don Martin said. "The trends on everything were good."
The start time for high schools was switched from 7:35 a.m. to 8:50 a.m. in the 2003-04 school year.

More overtime means higher turnover: study

Employers are demanding more overtime work and that is a key factor behind an increasing rate of turnover and workers compensation claims in the United States, according to a survey by Circadian Technologies, Inc., a Massassachusetts-based consultancy.

The Risks Of Prenatal Viral Infections,0,6490574.story?coll=hc-headlines-health

Genes that regulate cycles of sleep and wakefulness may also determine how well cancer patients respond to chemotherapy, according to researchers at Northwestern University.Oncologists have long argued that the benefits of chemotherapy vary depending upon the time of day it is administered. According to research published in the online edition of Proceedings of the National Academy of Sciences, mice given the cyclophosphamide in the late afternoon had better survival rates than mice given the chemotherapeutic agent in the morning.The researchers then tested mice bred to have mutations of two genes known to dampen the effect of the body's circadian rhythms, or the 24-hour cycle that influences functions such as body temperature, oxygen consumption, rest and activity.The mice with mutations in the two "clock" genes gene showed high sensitivity to chemotherapy, no matter when it was administered. By contrast, mice with a defect in another clock, which stops the body's internal clock at the body's most active point in the cycle, did not respond to the chemotherapy agent, no matter when it was administered.The researchers said the genes seem to influence survival of immune system cells and affect their sensitivity to chemotherapy.The findings could one day be used to help oncologists determine the best time of day to administer therapies and potentially lower doses of the toxic agents.

Are you SAD? Seasonal Affective Disorder can be depressing, but there are ways to beat it

With limited sunlight during the winter months, it makes it difficult to get outside after normal work hours. The temperature also drops after the sun goes down, making a jog even less appealing. As a result, some people suffer from symptoms of depression known as Seasonal Affective Disorder. It's related to seasonal variations of light during the winter months with symptoms subsiding with the return of spring and summer.

Space-age medicine for earthly practices

Researchers tackling the health concerns of space travelers are finding solutions for such problems as osteoporosis and sleep deprivation.

Categories:Clock News

Thursday, February 17, 2005

Circadian Dot Org

Dr. Roberto Reffinetti has, for quite a while now, maintained one of the best websites on chronobiology. You can learn about the work in his lab, about the tau-hamster, or move sideways to thermal biology. You can download his excellent online book "Philosophy of Physiology" or order his book "Circadian Physiology". You may follow the links to his scientific papers or to his papers on academic issues, mostly about sexual harassment. You can download some real laboratory data recorded from several (mostly unusual) lab organisms and download software to view and analyse the data. You can follow the link to the only online open-access journal in the field, Journal of Circadian Rhythms ( Finally, you can listen to music files with his compositions on circadian themes. All in one place, here:

Monday, February 14, 2005

Grand Rounds #21

The 21st installment of the medical Blog Carnival - Grand Rounds - is absolutely magnificient! Go to Sumer's Radiology Site and have your prescription filled:

Sunday, February 13, 2005

Human Clocks And Sleep

Since human chronobiology and sleep physiology are not my forte (I am more of an animal kind of guy), instead of writing a "Clock Tutorial" myself, I will point you to a website that does an excellent job of covering this area of research. Sleep Syllabus is designed as a course with severak short "chapters", each devoted to some aspect of human clocks and sleep, as well as evolutionary considerations. It is well worth bookmarking and reading.

Archives/Categories: Clock Tutorials

Tags: ,

Friday, February 11, 2005

Cutting Edge: February 2005 Journal of Biological Rhythms

Marta Muñoz, Stuart N. Peirson, Mark W. Hankins, and Russell G. Foster
Long-Term Constant Light Induces Constitutive Elevated Expression of mPER2 Protein in the Murine SCN: A Molecular Basis for Aschoff’s Rule?
J Biol Rhythms 20: 3-14.

Circadian rhythms in behavior, metabolism, and
physiology are based upon transcriptional/translational feedback loops involving
a core set of clock genes that interact to regulate their own expression. In
mammals, the SCN is the site of a master biological clock regulating circadian
locomotor rhythms. The products of the clock genes mPer1, mPer2, mCry1, and
mCry2 form essential components of both negative and positive elements within
the SCN oscillator. The primary aims of this study were to examine clock gene
abundance under longterm LL in an attempt to provide molecular correlates of the
lengthened tau and daily phase delays described by Aschoff’s rule. Wheel-running
behavior was recorded frommice maintained in eitherDDor LLfor 50 days. The
abundance of the clock genes mPer1, mPer2, mCry1, and mCry2 and their protein
products was then examined (every ~4 h) within the SCN using in situ
hybridization and immunocytochemistry. Under LL conditions, mPer1, mPer2, mCry1,
and mCry2 messages remained rhythmic, although the waveform of mCry2 was altered
compared to DD. In LL, mPER1, mCRY1, and mCRY2 protein levels were also rhythmic
and comparable to the patterns observed in DD. However, mPER2 is elevated and
constitutively expressed under LL. Thus, rhythmic expression of these clock
genes is not dependent on the rhythmic production of mPER2, and the acute
up-regulation of mPer1 and mPer2 described for short (nonparametric) light
pulses is not sustained under LL conditions. These findings suggest that mPER2
is important for the generation of phase delays in the molecular clockwork,
providing a possible molecular explanation for Aschoff’s rule: LL lengthens the
circadian period by inhibiting the degeneration of mPER2, and constitutively
elevated levels of mPER2 enhance the phase-delaying limb of the molecular

Hong-Nian Liu, Susumu Ohya, Shinji Furuzono, Jing Wang, Yuji Imaizumi, and Shinsuke Nakayama
Co-contribution of IP3R and Ca²+ Influx Pathways to Pacemaker Ca²+ Activity in Stomach ICC
J Biol Rhythms 20: 15-26.

Intracellular Ca2+ oscillations in interstitial cells
of Cajal (ICCs) are thought to be the primary pacemaker activity in the gut. In
the present study, the authors prepared small tissues of 100-to 300-µm diameter
(cell cluster preparation) from the stomach smooth muscle (including the
myenteric plexus) of mice by enzymatic and mechanical treatments. After 2 to 4
days of culture, the intracellular Ca2+ concentration ([Ca2+]i) was measured. In
the presence of nifedipine, a dihydropyridine Ca2+ channel antagonist,
spontaneous [Ca2+]i oscillations were observed within limited regions showing
positive c-Kitimmunoreactivity, a maker for ICCs. In the majority of cell
cluster preparations with multiple regions of [Ca2+]i oscillations, [Ca2+]i
oscillated synchronously in the same phase. Asmall number of cell clusters (8 of
53) showed multiple regions of [Ca2+]i oscillations synchronized but with a
considerable phase shift. Neither tetrodotoxin (250 nM) nor atropine (10µM)
significantly affected [Ca2+]i oscillations in the presence of nifedipine. Low
concentrations (40µM) of Ni2+ had little effect on the spontaneous [Ca2+]i
oscillation, but SK&F96365 (40µM) and Cd2+ (120µM) terminated it.
Applications of either 2-aminoethoxydiphenyl borate (10µM) or
xestosponginC(10µM) completely and rather rapidly (~2 min) abolished the
spontaneous [Ca2+]i oscillations. The results suggest that pacemaker [Ca2+]i
oscillations in ICCs are produced by close interaction of intracellular Ca2+
release channels, especially inositol 1,4,5-trisphosphate receptor (InsP3R) and
Ca2+ influx pathways, presumably corresponding to store-operated type channels.
Reverse transcription polymerase chain reaction examinations revealed expression
of TRPC2, 4, and 6, as well as InsP3R1 and 2 in ICCs.

Keisuke Hirai, Muneto Kita, Hiroyuki Ohta, Hisao Nishikawa, Yuu Fujiwara, Shigenori Ohkawa, and Masaomi Miyamoto
Ramelteon (TAK-375) Accelerates Reentrainment of Circadian Rhythm after a Phase Advance of the Light-Dark Cycle in Rats
J Biol Rhythms 20: 27-37.

In vivo pharmacological effects of ramelteon
(TAK-375), a novel, highly MT1/MT2-selective receptor agonist, were studied in
rats to determine ramelteon’s ability to reentrain the circadian rhythm after an
abrupt phase advance. Experiments were also conducted to assess the potential
cognitive side effects of ramelteon and its potential to become a drug of abuse.
After an abrupt 8-h phase shift, ramelteon (0.1 and 1 mg/kg, p.o.) and melatonin
(10 mg/kg, p.o.) accelerated reentrainment of running wheel activity rhythm to
the new lightdark cycle. Ramelteon (3-30 mg/kg, p.o.) and melatonin (10-100
mg/kg, p.o.) did not affect learning or memory in rats tested by the water maze
task and the delayed match to position task, although diazepam and triazolam
impaired both of the tasks. Neither ramelteon (3-30 mg/kg, p.o.) nor melatonin
(10-100mg/kg, p.o.) demonstrated a rewarding property in the conditioned
place-preference test, implying that MT1/MT2 receptor agonists have no abuse
potential. In contrast, benzodiazepines and morphine showed rewarding properties
in this test. The authors’ results suggest that ramelteon may be useful for
treatment of circadian rhythm sleep disorders without adverse effects typically
associated with benzodiazepine use, such as learning and memory impairment, and
drug dependence.

Michael R. Gorman, Magdalena Kendall, and Jeffrey A. Elliott
Scotopic Illumination Enhances Entrainment of Circadian Rhythms to Lengthening Light:Dark Cycles
J Biol Rhythms 20: 38-48.

Endogenously generated circadian rhythms are
synchronized with the environment through phase-resetting actions of light.
Starlight and dim moonlight are of insufficient intensity to reset the phase of
the clock directly, but recent studies have indicated that dim nocturnal
illumination may otherwise substantially alter entrainment to bright lighting
regimes. In this article, the authors demonstrate that, compared to total
darkness, dim illumination at night (<> 26 h. In the presence of dim nocturnal
illumination, however, a majority of hamsters entrained to Ts of 28 h or longer.
The presence or absence of a running wheel had only minor effects on entrainment
to lengthening light cycles. The results further establish the potent effects of
scotopic illumination on circadian entrainment and suggest that naturalistic
ambient lighting at night may enhance the plasticity of the circadian

Jin Ho Park, Matthew J. Paul, Matthew P. Butler, and Irving Zucker
Binocular Interactions in the Entrainment and Phase Shifting of Locomotor Activity Rhythms in Syrian Hamsters
J Biol Rhythms 20: 49-59.

To assess binocular interactions and possible ocular
dominance in entrainment of circadian rhythms, Syrian hamsters maintained in LL
were subjected for several weeks to schedules of eye occlusion with opaque
contact lenses. In separate groups, the opaque lens was inserted into the left
or right eye for 12 h at the same clock time each day. The left and right eyes
of other groups were alternately occluded for 12 h each day, with initial
occlusion of either the left or right eye for different groups. Amajority of
hamsters entrained their locomotor activity rhythm when 1 eye was occluded for
12 h. The modified visual input imposed by covering 1 eye is sufficient to
induce entrainment. Locomotor rhythms of most animals in which the 2 eyes were
alternately occluded for 12 h each day phasedelayed onset of activity during the
1st few days of the lensing procedure; activity onset then free ran with tau<>

Melanie Rüger, Marijke C. M. Gordijn, Domien G. M. Beersma, Bonnie de Vries, and Serge Daan
Nasal versus Temporal Illumination of the Human Retina: Effects on Core Body Temperature, Melatonin, and Circadian Phase
J Biol Rhythms 20: 60-70.

The mammalian retina contains both visual and
circadian photoreceptors. In humans, nocturnal stimulation of the latter
receptors leads to melatonin suppression, which might cause reduced nighttime
sleepiness. Melatonin suppression is maximal when the nasal part of the retina
is illuminated. Whether circadian phase shifting in humans is due to the same
photoreceptors is not known. The authors explore whether phase shifts and
melatonin suppression depend on the same retinal area. Twelve healthy subjects
participated in a within-subjects design and received all of 3 light
conditions—1) 10 lux of dim light on the whole retina, 2) 100 lux of ocular
light on the nasal part of the retina, and 3) 100 lux of ocular light on the
temporal part of the retina—on separate nights in random order. In all 3
conditions, pupils were dilated before and during light exposure. The protocol
consisted of an adaptation night followed by a 23-h period of sustained
wakefulness, during which a 4-h light pulse was presented at a time when maximal
phase delays were expected. Nasal illumination resulted in an immediate
suppression of melatonin but had no effect on subjective sleepiness or core body
temperature (CBT). Nasal illumination delayed the subsequent melatonin rhythm by
78 min, which is significantly (p= 0.016) more than the delay drift in the
dim-light condition (38 min), but had no detectable phase-shifting effect on the
CBT rhythm. Temporal illumination suppressed melatonin less than the nasal
illumination and had no effect on subjective sleepiness and CBT. Temporal
illumination delayed neither the melatonin rhythm nor the CBT rhythm. The data
show that the suppression of melatonin does not necessarily result in a
reduction of subjective sleepiness and an elevation ofCBT. In addition, 100 lux
of bright white light is strong enough to affect the photoreceptors responsible
for the suppression of melatonin but not strong enough to have a significant
effect on sleepiness and CBT. This may be due to the larger variability of the
latter variables.

Stacy A. Clemes, and Peter A. Howarth
The Menstrual Cycle and Susceptibility to Virtual Simulation Sickness
J Biol Rhythms 20: 71-82.

Virtual simulation sickness (VSS) is a form of
visually induced motion sickness that can result fromimmersion in a virtual
environment (VE). As in their susceptibility to the sickness induced by real
motion, womenhave been reported to be more susceptible than men to VSS, yet the
reason for this difference is not known. The aim of the current study was to
investigate the influence of themenstrual cycle on susceptibility to VSS in 16
naturally cycling women and to compare the responses of this group with control
groups consisting of 1) 16 premenopausal women taking a combined monophasic oral
contraceptive and 2) 16 men. All female participants were immersed in a
nauseogenic VE on days 5, 12, 19, and 26 of their menstrual/pill cycle. These
days were chosen because they fall in line with peaks and troughs of ovarian
hormone levels. Menstrual cycle phase was confirmed by salivary estradiol and
progesterone levels. A 4-week "pseudo-cycle" was assigned to the male
participants. Hormone analysis revealed that 9 participants in the experimental
group had been tested at the desired phases of their cycle. These participants
exhibited a significant increase in susceptibility to VSS on day 12 of their
cycle. The hormone analysis also showed that the cycles of the 7 remaining
members of the experimental group had not precisely followed the expected
pattern, and so these people had been tested on days that did not coincide with
peaks and troughs of ovarian hormone levels. No consistent variation in
susceptibility was observed over the cycle in these volunteers. In addition, no
change in susceptibility was observed over the pill cycle of the oral
contraceptive group nor over the pseudo-cycle applied to the male control group.
The authors conclude that susceptibility to VSS varies over the menstrual cycle
as a consequence of hormonal variation.
Florian Geier, Sabine Becker-Weimann, Achim Kramer, and Hanspeter Herzel
Entrainment in a Model of the Mammalian Circadian Oscillator
J Biol Rhythms 20: 83-93.

To adapt the timing of processes regulated by the
circadian clock to seasonally varying photoperiods, the phase relation between
the circadian clock and dusk or dawn ("phase of entrainment") must be tightly
adjusted. The authors use a mathematical model of the molecular mammalian
circadian oscillator to investigate the influence of the free-running period (tau)
and the shape of the PRC on the phase of entrainment. They find that a
phase-dependent sensitivity ("gating") of light-induced period gene
transcription enables a constant phase relation to dusk or dawn under different
photoperiods. Depending on the freerunning period tau and on the shaping of the
PRC by gating, the model circadian oscillator tracks either light onset or light
offset under different photoperiods. The study indicates that the phase of
entrainment of oscillating cells can be systematically controlled by regulating
both gating and the free-running period (tau).

Category: Cutting Edge Research


ClockNews #26: SAD and school-times

Guiding light

Therapy takes disorder's sufferers from SAD to glad in winter

Some snooze, some lose!localnews!education&s=1037645509111&tacodalogin=no

With a later school-start time, high-school students in the Winston-Salem/Forsyth County school system reported sleeping about 34 more minutes every night, doing more homework and falling asleep in class less frequently, according to a survey released this week.


Category: Clock News

Circadian Organization In Japanese Quail

Japanese quail (Coturnix coturnix japonica), also known as the Asian Migratory Quail, are gallinaceous birds from the family Phasianidae, until 1960s thought to be a subspecies of European migratory quail (Coturnix coturnix coturnix), but now considered to be a separate species, designated as Coturnix japonica. The breeding range of the wild population encompasses Siberia, Mongolia, northeastern China and Japan, while the wintering range is over south and southeastern Asia.

These birds were domesticated in Japan for song contests. During World War II most of the domesticated stock was lost and the remaining birds were crossed with imports from Korea and China and selected for egg and meat productivity. Wild and feral quail in Japan also migrate from island to island. Attempts to release Japanese quail in North America for hunting were not successful. Very fast maturation, prolific reproduction, and ease of husbandry, made the Japanese quail a popular laboratory animal in the fields of developmental, neuroendocrine and behavioral biology. As with most, if not all, temperate zone birds the reproductive system of Japanese quail is under the control of photoperiod: long photoperiods (above about 12.5 hrs) stimulate the development and maturation of the gonads.

Quail’s circadian system

The circadian system of Japanese quail is composed of several components including the pineal, the eyes and sites in the hypothalamus. Light can influence the circadian system of quail via several routes including the eyes, the pineal, and extraretinal-extrapineal photoreceptors in the brain.


In contrast to some other avian species, the pineal organ is not endogenously rhythmic in Japanese quail but pineal rhythmicity in constant conditions is driven by neural inputs from the central pacemakers. This neural input may involve adrenergic inputs from the superior cervical ganglia, but central control of pineal rhythmicity can persist even after removal of the superior cervical ganglia. Under rhythmic neural stimulation, the pineal gland secretes melatonin in a rhythmic fashion. A rhythm of pineal melatonin secretion can also be directly driven by 24 hr light-dark cycles because the pineal is directly photosensitive. Accordingly, in vitro, pineal melatonin rhythmicity can be directly driven by light-dark cycles but rhythmicity cannot be sustained in constant conditions. In addition to direct light perception, pineal melatonin rhythmicity may also be influenced by light perceived by the eyes and, possibly, by extraretinal photoreceptors in the brain. Retinal input to the pineal includes the optic tract because cutting the optic nerve abolishes the ability of retinally perceived light to influence the pineal melatonin rhythmicity.


By alternately patching each eye for a period of 12 hours in quail held in LL it is possible to entrain the melatonin rhythm of one eye 12 hours out of phase with the melatonin rhythm expressed by the other eye. Significantly, sectioning the optic nerves does not abolish the ability of an alternating-patch protocol to entrain the melatonin rhythm in the eyes 12 hours out of phase. Since cutting the optic nerves would deprive any extraocular clocks of entraining inputs, the fact that ocular rhythmicity is entrainable following optic nerve section proves that the clocks driving melatonin rhythmicity are located in the eyes themselves. Because blinding by complete eye removal causes quail to become arrhythmic in DD, it is likely that the eyes are not only biological clocks but they have an important role in helping to control the rest of the circadian system as well, that is, they are circadian pacemakers. The pineal and the hypothalamic oscillators are unable to sustain circadian oscillations in constant conditions in the absence of the ocular pacemakers. The Japanese quail are therefore unique among the vertebrates examined to date insofar as the eyes are essential for maintaining rhythmicity. The eyes of the pigeon are also important components of the circadian system but arrhythmicity in constant conditions requires removal of both the eyes and pineal.

The ocular pacemakers communicate with the pacemakers located in the hypothalamus neurally, presumably via the retino-hypothalamic tracts, as well as chemically, probably via the rhythmic synthesis and release of melatonin. The quail's eye shows a robust rhythm of melatonin synthesis and secretion in vivo and in vitro. Under a LD12:12 light cycle the blood shows a robust rhythm of melatonin content; about one third of the blood melatonin content is due to melatonin secretion from the eyes and the remaining two-thirds are secreted by the pineal. In continuous darkness (DD) the eyes contribute about half of the melatonin found in the blood. All normal quail exhibit a robust rhythm of body temperature in DD. Complete removal of the eyes, however, abolishes the rhythms of activity and body temperature in DD, while sectioning of optic nerves and leaving the eyes in situ renders about 25% of quail arrhythmic in DD. This implies that the eyes are coupled to the rest of the circadian system by both neural and hormonal inputs. The hormonal input is likely melatonin because optic nerve section does not affect the eye's ability to synthesize and secrete melatonin, and daily exogenous melatonin administration can entrain the circadian system of quail.

Suprachiasmatic Nuclei

The exact anatomical locus of the central pacemaker in quail is not known, but it is likely to reside in an equivalent of the mammalian suprachiasmatic nucleus. Lesions of the suprachiasmatic area that likely encompassed both the MHN and the LHRN rendered quail arrhythmic in DD. Recent studies in Japanese quail, utilizing molecular techniques point to the medial SCN (MHN) as the site of the biological clock, as the mRNA of the clock genes Per, Clk and Cry cycle in this region but clock gene expression is absent in the LHRN. However, either immature males or animals of undeclared sex and age were used in these studies. It is possible that clock genes may be expressed in the LHRN of mature birds under the control of reproductive hormones. In chicken, for example, estradiol had been reported to elicit the expression of the clock gene cry1 in the MHN. Interestingly, in house sparrows, a small subset of individuals exhibited expression of clock gene RNAs in the LHRN, but the age and sex of these birds was not reported. A recent study describes a neural connection between the two sets of nuclei, suggesting that both pairs may contain circadian pacemakers.

Retinal and Extraretinal photoreception

The circadian systems of non-mammalian vertebrates are characterized by multiple photic inputs: the eyes, extraretinal receptors in the brain, and pineal photoreceptors. Entrainment to 24 hr LD cycles is possible after removal of the eyes and/or pineal in many species of fish, amphibians, reptiles and birds. Significant amounts of light can penetrate the skull and reach the brain of vertebrates. The extraretinal photoreceptors are sensitive to intensities of light as low as the equivalent of moonlight. The exact location of extraretinal photoreceptors is not clearly established. That these receptors are located in the brain is shown by blocking light to the head which abolishes entrainment in blinded house sparrows, frogs and lizards. Also, localized illumination of the brain via fiber optics can entrain the activity rhythm of the lizard Sceloporus olivaceus.

Extraretinal photoreceptors are also involved in the photoperiodic response of non-mammalian vertebrates. Russell Foster and Sir Brian Follett showed that the extraretinal photoreceptors mediating the reproductive response to photoperiod in the Japanese quail likely employ a photopigment with wavelength sensitivity similar to that of rhodopsin. A number of studies in birds have localized the extraretinal photoreceptors mediating the photoperiodic response to the medial basal hypothalamus, although other brain sites have occasionally been implicated as well. However, it is not known if the extraretinal photoreceptors mediating entrainment are identical to the extraretinal photoreceptors mediating the photoperiodic response. Studies suggest multiple types of brain photopigments and at least two types of photoreceptors. Foster and colleagues suggest that CSF-contacting neurons are the strongest candidates for deep brain photoreceptors in lampreys, reptiles and birds, while classical neurosecretory neurons (NMPO cells) are photosensory in fish and amphibians.

That the eyes contribute to entrainment has been demonstrated in some fish, lizards and birds. The relative contribution of retinal and extraretinal photoreceptors to entrainment has not been established. Because the extraretinal photoreceptors have not been definitively localized, it has not been possible to determine if entrainment persists in animals with intact eyes but without extraretinal and pineal photoreceptors. Recently, molecular techniques were used to localize opsin reactivity to the nucleus ventromedialis of the forebrain in a lizard, Podarcis sicula. Inhibition of the opsin in this area by anti-sense RNA abolished extraretinally mediated circadian photoentrainment.

In the quail, entrainment of the pineal melatonin rhythm occurred if the eyes were "patched" for 12 out of every 24 hours in birds otherwise held in LL. The entrainment pathway from the eyes to the pineal involved the optic nerve because optic nerve section abolished entrainment in response to the patching regimen. Interestingly, a similar experiment performed in pigeons failed to elicit entrainment of the pineal melatonin rhythm.

Foster and colleagues have proposed a theoretical explanation for why both retinal and extraretinal photoreceptors may coexist in non-mammalian vertebrates. The optical nature of the eye allows a focused representation of the environment: large numbers of photons must be sampled quickly to build a spatial image of the world. The eye measures brightness in a particular point in space (radiance) but not from the whole field of view (irradiance). On the other hand, entrainment of circadian pacemakers (or perception of daylength) requires irradiance detection, but not a spatial imaging capability. Extraretinal photoreceptors are well-suited for irradiance detection because overlaying tissues scatter light. Because mammals lack extraretinal photoreceptors, Foster and colleagues hypothesize that the random projections of retinal ganglion cells to the location of the mammalian circadian pacemaker (the suprachiasmatic nucleus) could result in a form of irradiance detection in mammals. Behavioral studies in mammals, however, have failed to detect extraretinal photoreception.

Role of the reproductive system

In some birds, steroid hormones can have an effect on the circadian system. For instance, injections of testosterone induce splitting of the activity rhythm in male starlings (Sturnus vulgaris) and an increase in the duration of the active phase of the locomotor rhythm. Also, sexually mature male Japanese quail show a longer freerunning period than immature birds and exogenous administration of testosterone increases the freerunning period in DD of castrated male quail. An important role for the reproductive hormones in controlling the circadian system of female Japanese quail is seen because: (1) the freerunning activity, body temperature, and oviposition rhythms show an average periodicity of 26.7 hours in birds held in LL whereas the average freerunning period of activity and body temperature of non-ovulating birds in DD is 22.5 hours, (2) castration abolishes rhythmicity in female quail exposed to LL, and (3) normal birds are arrhythmic in LL until the onset of oviposition, whereupon the birds begin showing rhythms of activity and body temperature with the same periodicity as the rhythm of oviposition.

Placing permanent patches over both eyes of female quail in LL results in "splitting" of the body temperature rhythm into two circadian components: a "short" component driven by the pacemaker in the eyes which are experiencing DD, and a "long" component driven by the ovulatory cycle. The reproductive system remains active in eye-patched birds in LL because the photoperiodic response is stimulated directly by light via extraretinal photoreceptors in the brain. The two components in eye-patched birds in LL show constantly changing phase-relationships with each other. Significantly, at some phases ovulation is either delayed or inhibited, suggesting a phase-dependent effect of the oscillators on reproductive function.

Light can influence the system via three routes: the eyes, the pineal and the deep brain extraretinal photoreceptors. Extraretinal photoreceptors are involved both in the transduction of photoperiodic information and in entrainment. The pineal is not autonomously rhythmic but its rhythm of melatonin synthesis and secretion is driven by the rest of the system through a neural pathway that may, or may not, involve the superior cervical ganglia. The central pacemakers (SCN?) are considered to be "complex" pacemakers; that is, each SCN is, itself, composed of a set of coupled circadian clocks; that is, many, if not most, of the neurons comprising the SCN are competent clocks. The eyes are the sites of pacemakers that can drive a rhythm of melatonin synthesis and secretion. The ocular pacemakers are coupled to the rest of the system via the cyclic synthesis and release of melatonin and via a neural pathway, possibly the retino-hypothalamic (RH) tract.

Because the hypothalamic pacemakers (SCN) are, themselves, composed of multiple cellular clocks, under certain experimental conditions it is possible to cause these complex pacemakers to split into two circadian components: a short-period component driven by the ocular pacemakers and a long-period component driven by feedback from gonadal steroids. The precise location of the hypothalamic pacemaker is unknown but it is likely localized in a structure homologous to the mammalian SCN (either the MHN and/or LHRN). The central pacemakers, or perhaps some portions of them, may be directly sensitive to the steroid hormones. Mammalian SCN expresses estrogen receptors. Similar studies in birds did not reveal steroid receptor expression in the putative SCN, yet none of these studies were conducted in reproductively mature females. Alternatively, the effects of steroids on the SCN may be indirect, via centers in the preoptic area, which are known to contain neurons that express steroid receptors.

Sex differences and the role of reproductive system in circadian function are much more dramatic in the Japanese quail than in any other organism studied to date. Thus, the Japanese quail is an ideal laboratory model for studies of interactions between circadian and reproductive systems and of sex differences in such interactions. Interactions between the circadian and reproductive systems seem to act in both directions. In one direction, the circadian system controls daily rhythms of egg-laying and it is also crucially involved in daylength measurement used for seasonal timing of reproduction. On the other hand, the reproductive state affects properties of the circadian clock.

Archives/Categories: Clock Tutorials

Circadian Organization In Non-Mammalian Vertebrates

I have previously described the basic properties of the circadian organization in mammals. Non-mammalian vertebrates (fish, amphibians, reptiles and birds) have more complex circadian systems than mammals. While the suprachiasmatic area remains a site of circadian pacemakers, it is, unlike in mammals, not the only such site.

The pineal organ, which in mammals is a purely secretory organ, is directly photosensitive in other vertebrates (with the exception of snakes) and is a site of a circadian pacemaker. Retinae of the eyes are also sites of circadian pacemakers in at least some non-mammalian vertebrates. Extra-retinal photoreceptors that can mediate entrainment of circadian clocks are also found deep inside the brain.

Thus, the non-mammalian circadian system is composed of multiple pacemakers (eyes, pineal, SCN) and multiple photic inputs (eyes, pineal, deep-brain photoreceptors). These structures communicate with each other neurally and humorally and provide a single synchronized output in the rhythmic behavior of the animal.

However, the properties and relative importance of each structure can differ between species. For instance, pinealectomy has different effects in different species of lizards, leading to either splitting (left), arrhythmicity (middle),or period-change (right):

While research has been done in lampreys, some fish, frogs, and lizards, most of the work on non-mammalian vertebrates has been conducted in birds. I will return, in the future, to more detailed reviews of chronobiology of other vertebrate classes, but today, I will concentrate on birds.

Birds (click for a review)

The circadian system of birds involves several components: a central hypothalamic clock (SCN), the pineal organ, the retinae and extraretinal photoreceptors. These elements show different degrees of involvement in the production of the circadian output in different avian species. Some components (such as the SCN and pineal, or the eyes and the SCN) may be coupled together via the hormone, melatonin.

In house sparrows, the pineal is the master pacemaker of the circadian system and pinealectomy results in complete arrhythmicity. In European starling, pinealectomy can result in period change or arrhythmicity, depending on the individual. In pigeons, neither blinding alone nor pinealectomy alone disrupts circadian rhythms, yet removal of both the pineal and the eyes results in complete arrhythmicity.

There is some controversy concerning which hypothalamic nucleus in birds is the homologue of the mammalian SCN. Classical anatomical studies suggest that the avian SCN resides adjacent to the preoptic recess of the third ventricle and the optic chiasm in the nucleus termed the "medial hypothalamic nucleus" (MHN), also sometimes referred to as the "periventricular preoptic nucleus" (PPN) whereas studies of the termination of the retinohypothalamic tract (RH) suggest that the SCN resides more caudally, between the supraoptic decussations and the vLGN, in a nucleus termed the "lateral hypothalamic retinorecipient nucleus" (LHRN), also termed the "visual SCN". However, a number of studies in birds, including cholera toxin mapping of retinal projections in pigeons, show that both the MHN and the LHRN can receive significant retinal input. Immunohistochemical analyses of the various neurochemicals and neurotransmitters could not demonstrate complete homology between the mammalian SCN and either MHN or the LHRN.

Several investigators have lesioned the MHN of birds to determine if these lesions would lead to loss of rhythmicity in the locomotor activity of animals held in continuous darkness (DD), but the total number of species (or individuals) examined is small and, in some cases, the lesions may also have damaged the LHRN as well. Arrhythmicity is caused by MNH lesions in Java sparrows, Japanese quail and house sparrows. In house sparrows, it is the LHRN which shows a circadian rhythm of metabolic activity as measured by 2-deoxy[14C]glucose uptake. This rhythm is abolished by pinealectomy and restored by daily melatonin injections. In pigeons, lesions of either of the two nuclei did not abolish rhythmicity, although some disruptions of the activity rhythm could be seen. In chicks, lesions of the LHRN abolished the circadian rhythm of epinephrine turnover in the pineal, while the lesions of the MHN had no effect. Recent data on expression of RNA for the clock genes in Japanese quail, Java sparrow, chicken and pigeon suggest the MHN as the locus of the circadian pacemaker, although these studies were performed either in immature males or the sex of the animals was not reported, thus leaving open the possibility that the LHRN may have a function in ovulating females. In the house sparrow, however, circadian expression of the clock gene per was observed in both the MHN and the LHRN, but the sex, age and reproductive status of these individuals were not noted.

It is likely that the central clocks in birds are, themselves, multioscillator in nature: that is, each "clock" in the suprachiasmatic area is composed of a number of interacting (coupled) circadian oscillators. Recent studies in mammals have shown that a number of individual neurons within the SCN are capable of expressing circadian rhythms of electrical activity. Furthermore, the period of the behavioral rhythm of locomotor activity in mammals is correlated with the average period of the rhythms of electrical activity expressed by individual SCN neurons.

Next time, I will go into details of the circadian organization of one avian species as an example of a non-mammalian vertebrate.

Archives/Categories: Clock Tutorials

Thursday, February 10, 2005

Sleep Blog

Rebel Doctor ( has decided to quit rebelling and fall asleep ( No, really, he is an MD and a sleep specialist. I am a chronobiologist studying circadian rhythms, not sleep, and may not be able to answer the fine details of clinical aspects of sleep, so if you have such questions, go there and ask the Sleep Doctor.

Wednesday, February 09, 2005

Tangled Bank #21

The new Tangled Bank, a collection of best blog writing about biology, nature and medicine, is now up:

Tuesday, February 08, 2005

Clock News 25: Clocks and Cancer

Chemo On The Clock,0,6490574.story?coll=hc-headlines-health
Genes that regulate cycles of sleep and wakefulness
may also determine how well cancer patients respond to chemotherapy, according
to researchers at Northwestern University.Oncologists have long argued that the
benefits of chemotherapy vary depending upon the time of day it is administered.
According to research published in the online edition of Proceedings of the
National Academy of Sciences, mice given the cyclophosphamide in the late
afternoon had better survival rates than mice given the chemotherapeutic agent
in the morning.The researchers then tested mice bred to have mutations of two
genes known to dampen the effect of the body's circadian rhythms, or the 24-hour
cycle that influences functions such as body temperature, oxygen consumption,
rest and activity.The mice with mutations in the two "clock" genes gene showed
high sensitivity to chemotherapy, no matter when it was administered. By
contrast, mice with a defect in another clock, which stops the body's internal
clock at the body's most active point in the cycle, did not respond to the
chemotherapy agent, no matter when it was administered.The researchers said the
genes seem to influence survival of immune system cells and affect their
sensitivity to chemotherapy.The findings could one day be used to help
oncologists determine the best time of day to administer therapies and
potentially lower doses of the toxic agents.

Monday, February 07, 2005

ClockNews #24: Melatonin Affect Reproduction, and Clocks In Space

Popular supplement melatonin found to have broader effects in brain than once thought

"It really amazes me that melatonin is available in any pharmacy," Bentley said. "It is a powerful hormone, and yet people don't realize that it's as 'powerful' as any steroid. I'm sure that many people who take it wouldn't take steroids so glibly. It could have a multitude of effects on the underlying physiology of an organism, but we know so little about how it interacts with other hormone systems."

Space-age medicine for earthly practices

Meanwhile, helping people both on Earth and in space get a good night's sleep without relying on medications is the goal of George Brainard, PhD, professor of neurology at Jefferson Medical College in Philadelphia.
"Even in short flights, astronauts may go from getting seven to eight hours of sleep a night to getting only six or less. Something happens to [their] bodies that leads to sleep reduction," he said.
Although losing an hour per night might not seem too terrible, on a long mission those lost hours could add up to serious deprivation. Dr. Brainard and his colleagues are now working with light treatment to determine whether increasing the power in the short wave length, or the blue portion, of the spectrum can help maintain astronauts' circadian rhythms and keep sleep cycles at an adequate level.
The technique wouldn't just be for outer space. "One-fifth of the working population in the United States and most other industrialized countries does shift work. They are working at a time that they are biologically designed to be sleeping and trying to sleep at a time they are designed to be awake," Dr. Brainard said.

Categories: Clock News

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Sunday, February 06, 2005

Clock Tutorial #7: Circadian Organization in Mammals

The principal mammalian circadian pacemaker is located in the suprachiasmatic nuclei (SCN) of the hypothalamus. The general area was first discovered in 1948 by Curt Richter who systematically lesioned a number of endocrine glands and brain areas in rats. The only time he saw an effect on circadian rhythms was when he lesioned a frontal part of hypothalamus (which is at the base of the brain) immediatelly above the optic chiasm (the spot where two optic nerves cross). Later studies in the 1970s narrowed the area to a small pair of nuclei, each composed of about 10,000 neurons. Similar studies (lesions) were performed in a number of other species of mammals, confirming that SCN is the pacemaker in all mammals.

[Image: Rat Brain]
A serendipitous discovery of a circadian period mutant (Tau-mutant) by Martin Ralph, then in Mike Menaker's lab, provided an opportunity to further test the hypothesis that SCN is, indeed, the pacemaker, and not just a way-station for the circadian information (as was still a possible alternative explanation of the lesion studies). The wild-type Golden hamsters have an endogenous period of almost precisely 24 hours. The homozygous tau-mutants exhibit a period of about 20 hours (while heterozygotes have an intermediate period of about 22 hours). Ralph transplantated SCNs between wild-type and Tau-mutant hamsters. What he saw was that the period of the overt rhythms of the hosts was always equal to the period of the transplanted SCN of the donor, i.e., a mutant hamster with a wild-type graft exhibited a 24-hour rhythm, while a wild-type mutant with implanted mutant SCN showed a periodicity of 20 hours. He rightly concluded that the SCN contained within itself all the information needed for the proper functioning of the circadian system, including the most basic property of the rhythm - its period - thus the SCN is, by definition, the pacemaker of the hamster circadian system.

Wild-Type Hamster

Tau-Mutant Hamster

Results of Transplantations

Each SCN is, itself, a multi-oscillator system as individual SCN neurons can show different endogenous periodicities in vitro. In vivo, the individual neurons are coupled together to produce a single circadian output. Recent studies indicate that some of the coupling is not synaptic (via neurotransmitters) but electrical (via "gap junctions"). More recent studies uncovered an internal division within each nucleus in what are termed "core" and "shell", each with slightly different properties, one with slightly shorter innate period than the other, and one recieving the majority of the neural input from the eye.

The eye is the only route for the information about external light conditions into the mammalian circadian system. The photic (light) input to the SCN comes from the ganglion cells of the retina via a direct mono-synaptic retinohypothalamic tract (i.e., the ganglion cell of the retina sends one long process all the way to the SCN, so the signal is NOT transduced via a chain of several successive neural cells). Non-visual photoreception, involved in circadian entrainment, pupillary reflex and control of mood, appears to be mediated differently from vision. Although photoreceptor cells (rods and cones) appear to play a role, most attention recently has been given to a small subset of retinal ganglion cells that project directly to the SCN and have been shown to be directly photo-sensitive. The identity of the photopigment used by these cells remains a subject of much debate, with melanopsin and cryptochrome being the major candidates. As persuasive data have been reported supporting an important role for each of these pigments, it is likely that both are involved, playing specific yet somewhat overlapping roles in non-visual photoreception.

[Image - Mammalian Retina]

The output of the clock is coupled to various effector areas of the brain including other areas of the hypothalamus, as well as to the superior cervical ganglia which provide adrenergic innervation of the pineal gland. Driven by the daily rhythm of adrenergic stimulation, the pineal synthesizes and secretes its hormone (melatonin) into the bloodstream during the night, but not during the day. In mammals, the profile of melatonin secretion is used for the interpretation of daylength in the photoperiodic response. There is no endogenous rhythmicity in the mammalian pineal - all pineal rhythms are driven by neural inputs from the SCN. The retina, on the other hand, is a site of a circadian clock but the retinal clock appears to drive rhythms within the eye itself and it does not influence the rest of the circadian system.

[Image - Primate brain]

Apparently, all cells in mammalian body contain circadian clocks. These cells, in contrast to cells of the SCN, are called peripheral clocks or oscillators. Peripheral circadian oscillators cannot maintain rhythmicity in the absence of the SCN. When placed in a dish, peripheral clocks may undergo a few oscillations before becoming arrhythmic. In contrast, SCN cells cycle indefinitely in vitro. In addition, peripheral oscillators are not directly light sensitive, so the only way they can be entrained is via neural or hormonal signal driven by the pacemaker in the SCN. A number of humoral signals have been hypothesized to play this role, including cortisol and melatonin. The dynamics of entrainment of peripheral clocks appears to vary between the tissues, e.g., liver cells being much slower to reset to a new light-dark schedule than cells in some other organs. This observation can potentially explain jet-lag as a result of internal desynchronization between various peripheral oscillators.

Sex differences have been noted in mammalian circadian systems and a number of studies have shown an interaction between the circadian and the reproductive systems. The role of circadian rhythms in the measurement of daylength as an environmental signal for seasonal reproduction has been demonstrated quite decisively in mammals. An involvement of the circadian system in the timing of ovulation (primarily in rodents) is not as clear, although some persuasive data have been published. Effects of implants of steroid hormones have been seen in female rodents, both castrated and intact, with slight increases in period effected by estradiol. This effect is blocked by simultaneous application of progesterone and is also seen in embryonically feminized males.

Archives/Categories: Clock Tutorials

ClockNews#23: ShiftWork, Breast Cancer and Zebrafish (again)

12-hour shifts not good for body or soul

There arises a conflict between the biological imperative
for sleep and the social demands for performance. This leads to one question:
"What happens to one's performance when one's sleep is deprived?"
Breast Cancer Mystery Frustrates Scientists,0,2553.story?coll=hc-headlines-health

Their theory that artificial light can cause breast cancer
is simple. Prolonged periods of exposure to artificial light disrupt the body's
circadian rhythms - the inner biological clocks honed over thousands of years of
evolution to regulate behaviors such as sleep and wakefulness. The disruption
affects levels of hormones such as melatonin and the workings of cellular
machinery, which can trigger the onset of cancer, Stevens theorizes.
Biological clock lights up

With its relatively small genome and its ability to produce
mutations that are analogous to those in humans, the humble zebrafish already is
a valuable tool in genetics research. But it just got better: Researchers at the
University of Houston have developed a transgenic zebrafish that glows according
to its biological clock.

Friday, February 04, 2005

Circadian Way

There is a tiny little street in Chapel Hill, NC that is called Circadian Way, just off of Hillsborough Rd. Check the map:
Perhaps I'll drive there tomorrow. It would be so fitting if I lived there!

Thursday, February 03, 2005

ClockNews #22: Sex, Drugs and Alcohol

Effective Cancer Treatments Follow the Clock

Oncologists have long thought that cancer treatments
tend to be more effective at certain times of day. But they have been unable to
turn this knowledge into practice, because they did not understand the
phenomenon well enough. Now, researchers have discovered a molecular mechanism
that explains why sensitivity to anti-cancer drugs changes with the clock. They
said their findings could lead to new drug treatments that may be more effective
because they harness the power and precision of the body's internal
What Does An Airline Traveler Have In Common With A Glowing Fish?
In William Gibson’s novel Pattern Recognition, the
protagonist posits a theory of jet lag: "Souls can’t move that quickly, and are
left behind, and must be awaited, upon arrival, like lost luggage."
has yet to address the issue of a spiritual speed limit, but it is generally
accepted that jet lag actually results from the upset of the body’s circadian
clock, a biochemical pacemaker that dictates daily rhythms in sleep and
wakefulness as well as body temperature and metabolic activity. In humans, the
circadian rhythm responds to many factors, but daytime–nighttime (or, more
precisely, light–dark) cycles are one major regulator. It is possible to
gradually reset an upset circadian clock; if travelers remain in the same place
for long enough, their circadian rhythm will eventually adjust to the new time
zone and ambient light patterns, and the symptoms of jet lag will
New drugs to help folks sleep

- The impending rollout of a new medicine for
long-term treatment of insomnia has the potential to make its manufacturer
millions - and to further acceptance of the sleeping pill, traditionally a dark
character in the prescription drug world.
Some sleep-disorder specialists
are hailing the new drug. But others caution that chronic use of sleeping pills
is ill advised.
Lunesta, made by Sepracor of Marlborough, Mass., is the
first insomnia drug approved by the federal Food and Drug Administration for
long-term use. With similar drugs, including market leader Ambien, the FDA
advises treatment should last no more than 10 days, although a doctor can
prescribe it longer.
"Night after night after night" is Sepracor's slogan
for the new drug.
Gen-X on Ice
Midnight, of course, is a euphemistic term — during
the summer months of the team’s residence, the sun circles endlessly above the
horizon, illuminating the landscape with a perpetually brilliant glare.
Polarized sunglasses are a must, as are sleep masks — one of the major problems
one experiences down here is an inability to shut off when it is time to go to
sleep. Without the cue of darkness to trigger the body’s diurnal response,
circadian rhythms are thrown into flux and eventually you just have to accept
that it is time to rest no matter what the sun is doing.
Sleeping problems - think about sex not sheep,2106,3173895a7144,00.html

Counting sheep might work for some, but sleep
specialist Fiona Johnston can think of better things to recommend to people
having trouble nodding off at bedtime.
"If it relaxes you, that's fine, but
it wouldn't relax me - I'd find it utterly boring," she said today.
"I have
better things to do with my imagination and so do most people."
lists other options in her book, Getting a Good Night's Sleep, published this
week in an updated third edition to take in recent developments, including
legislative changes.
Among possible visualisations are floating away in a
hot-air balloon, entering a secret bedroom containing memories of a happy
childhood, or going for a walk on a beach.
Another suggestion that "needs no
explanation" is thinking about good sex, "because the storyline can be very
compelling, making it easy to keep your mind free of worries".
Drinking alcohol before bed can ruin sleep quality

But drinking before bed can not only ruin your
night's sleep and your productivity the next day, but could also inflame sleep
disorders and possibly lead to alcoholism, Coulter said.
Alcohol can
suppress REM, or rapid eye movement, stage of sleep, the doctor said.
even though you're falling asleep quicker, you're getting less deeper, quality
sleep," he said.

Archives/Categories: Clock News

Clock Tutorial #6: To Entrain Or Not To Entrain, That Is The Question

Let's now continue our series of Clock Tutorials with an introduction to some phenomena (and related terms and concepts) observed in the laboratory in the course of doing standard circadian experiments. Such experiments usually involve either the study of properties of freerunning rhythms (check the old tutorials, especially CT2 and CT 4 for clarification of basic terms and concepts), or the analysis of entrainment of rhythms to environmental periodicities.

Entrainment is a process by which a biological rhythm is synchronized by an environmental periodicity. In other words, it is the way an external cycle forces the biological clock to assume the period of the environmental cycle. Imagine that your wristwatch is not very precise and you have to, every day when you wake up in the morning, reset it to the real local time. This is exactly what the dawn of the day does to myriads of biological clocks residing in gazillions of organisms strewn all over the surface of the Earth (and oceans) every day. It phase-locks a particular phase of the circadian rhythm to the particular phase of the day-night cycle (e.g., wake-up time phase to the dawn phase).

Often, it is not immediatelly clear from an actograph if the apparently entrained rhythm is really entrained. In some cases the environmental cue that is used, e.g., light, exerts a masking effect. Masking is a direct effect of the environment on the observed/measured output, thus on the hands of the clock as opposed to the core machinery of the clock. For instance, light may directly inhibit locomotor activity in a nocturnal animal (e.g., mouse) or stimulate a rise in body temperature in a diurnal animal (e.g., a bird), regardless to its possible effect on the clock itself.

Thus, it is neccessary to conduct experiments in such a way that a clear distinction between entrainment and masking can be elucidated. This involves, usually, a freerun-entrainment-freerun protocol, in which the organism is observed in constant conditions for at least a few days, followed by an entrainment regime for at least several days, followed by another bout of monitoring in constant conditions. Visual inspection of the actograph is usually sufficient to discriminate between masking and true entrainment. One first draws a straight line through the onsets of daily activity during the freerun at the top of the actograph. If extending that line through the remainder of the graph places it along the onsets of the second freerun, we conclude that the effect is masking. If the second freerun is "displaced" on the graph compared to the extended line, we are assuming true entrainment. Here is a schematic visual representation of both situations, assuming a diurnal (day-active) endothermic (warm-blooded) animal:

These actographs are double-plotted for aid in visual inspection of the data. A graph is double-plotted by placing the data of Day 2 both immediately under the Day 1 and immediatelly to the right of Day 1. Day 3 data are also duplicated - on the right of Day 2 in the second row and below Day 2 in the third row, and so on.

As you can see, a light-dark cycle (as indicated by a white-dark light bar on top of the graph) entrains the rhythm in the graph on the top, but the temperature cycle (indicated by a line on top of the graph, W=warm, 20 Celsius, H=hot, 25 Celsius, C=cold, 15 Celsius) masks the underlying freerun of the clock in the bottom graph. Thus we conclude that, in this organism, light-dark cycle is an entraining cue (Zeitgeber), while the temperature cycle is not.

Additional aspects of the records are also helpful. For instance, you may notice that it took a few days of transients until the rhythm entrained (phase-locked) to the LD cycle. This would not have happened with masking - the shift would have been abrupt. Likewise, at the end of the LD cycle, the freerun starts with the onset-phase (CT0 - Circadian time) appearing at the time predicted from the onset-phase of the entrained rhythm (ZT0 - Zetigeber time). In the case of masking, there is often an abrupt (apparent, not real) phase-shift at this point.

Of course, this is just a beginning of your work. Now that you know how your organism responds, you can begin to study the details of physiology of the clock, its entrainment by light, and its non-entrainment by temperature, as well as think about it in evolutionary/adaptive terms.

Not all environmental cycles have such a clear-cut result as the two shown above. It is not necessary that a cycle is either a perfect Zeitgeber or completely ignored by the circadian system. There are shades of grey, too. For instance, some cycles are weak Zeitgebers. Here are some examples of possible results and how they look when plotted as actographs:

The first graph shows a phenomenon called relative coordination. From the graph you can see that the rhythm is entrained for a few days, then starts drifting (freerunning) away. When it reaches a particular phase relationship with the environmental cycle, it temporarily entrains again, etc. A more abrupt period-change related to this phenomenon is sometimes termed scalloping (middle graph). If changing phase-relationship between the rhythm and the Zeitgeber results not just in changes of period, but also abrupt changes in phase, this is called phase-jumping, as seen on the graph on the bottom.

One way of studying entrainment to natural cycles is to force the clocks to entrain to unnatural cycles and chronobiologists have been very creative in inventing strange lighting protocols. I will write about those in more detail once I get to the topic of photoperiodism, but for now, let me introduce you to the two of the simplest types of non-natural cycles that are regularly used in the laboratory, their utility in research, and what kinds of phenomena were noted when these were employed. As light is the strongest and most important Zeitgeber, most of the research employed cycles of light and darkness. However, cycles of other cues (e.g., temperature) have also occasionaly been studied, both in natural and non-natural versions.

Skeleton photocycles contain a normal dark phase, but the dark phase is broken up into three components: the dawn (light), the daytime (dark - lights are off), and dusk (light). Thus a full-photoperiod light-dark cycle composed of 12 hours of light and 12 hours of darkness (LD 12:12), when done as a skeleton photoperiod would look, for instance, like this: 1 hour of light, 10 hours of dark, 1 hour of light, 12 hours of dark (LDLD 1:10:1:12). The duration of light pulses that mimic dawn and dusk is arbitrary, e.g., one can choose to use 1 second, or 3 hours, depending on the hypothesis one is testing. If the dawn-pulse and the dusk-pulse are of the same duration (e.g., each is 2 hours long), this is called a symmetrical skeleton photoperiod. If one is longer than the other (usually dawn longer than dusk, e.g., a 6-hour dawn pulse and a 1-hour dusk pulse), this is an assymetrical skeleton photoperiod.

If the stimulus used is just having a masking effect, there will be a response to the two pulses, but no response seen during the darkness in-between the pulses (bottom plot). On the other hand, if the skeleton photocycle results in true entrainment, the observed overt rhythm will look the same whether it is exposed to the full or to the skeleton cycle (top and middle plots):

One interesting observation from the studies of entrainment by skeleton photoperiods is the bistability phenomenon. A full photoperiod will entrain the biological clock no matter how short or long is the photoperiod, i.e., the duration of the light portion of the light-dark cycle. Thus LD 1:23, LD 3:21, LD 6:18, LD 8:16, LD 10:14, LD 12:12, LD 14:10, LD 16:8, LD 18:6, LD 21:3 and LD 23:1 are all equally likely to entrain a clock. On the other hand, with skeleton photocycles, photoperiod matters. The biological clock "prefers" short photoperiods to long photoperiods. Thus, when exposed to a skeleton photocycle that attempts to entrain to a cycle mimicking a long photoperiod, the rhythm will, instead, reverse the "night" and "day" (often with an abrupt phase-jump). For instance LD 1:16:1:6 will not be understood by the clock as LD 18:6, but as LD 6:18.

In nature, many nocturnal (night-active) organisms actually live in skeleton photoperiods. During the night, they are out foraging. During the day, they are hiding (and sleeping) deep in the darkness of their burrows or caves. The only light they see are very brief periods during dawn and dusk. Thus, this type of lighting protocol in the laboratory has an additional utility in that it studies a natural phenomenon.

On the other hand, outside of science-fiction, there is nothing natural about T-cycles. With these, the total duration of the cycle (e.g,. L + D = T ) is not equal to 24 hours. Usually groups of organisms are exposed to a systematic array of T-cycles, e.g., LD 6:6, LD 6:9, LD 6:12, LD 6:15, LD 6:18, LD 6:21, LD 6:24, LD 6:27, LD 6:30, etc. The first four are shorter than 24 hours, the fifth is exactly 24 hours, and the last four are longer than 24 hours. If an organism is exposed to a T-cycle to which it cannot entrain, it may, instead, exhibit a phenomenon called frequency demultiplication. For instance, it may entrain to LD 6:6 as if it was an LD 18:6 (or a skeleton cycle LDLD 6:6:6:6). In other cases, the rhythm may show relative coordination, or just ignore the cycle altogether and freerun through the whole experiment.

In some cases, for the ease of visual inspection, the actograph is not folded at 24 h, but at the period of the cycle. For instance, on the top is a schematic of entrainment to a T-cycle folded at 24 hours, and on the bottom is the same record folded at 22 hours:

This type of protocol uncovers the limits of entrainment for each species. Most rodents used in laboratory research have very narrow limits of entrainment, with T (period of the cycle) ranging somewhere between 23h and 25h. On the other hand, plants, fungi and protists often have very large limits of entrainment. Of course, there is quite a lot of variation between related groups, thus sparrows have much narrower limits of entrainment than quail, although both are birds. Adaptive function of limits of entrainment has over the years been the subject of some study, but no clear conclusions can be made yet. The differences between phyla are particularly difficult to understand, while differences within smaller group sometimes correrelate with territory-size, burrowing vs. surface nesting, diurnality vs. nocturnality, or sedentary vs. migratory life history. For instance, the limits can change within the same animal, depending if it is in its migratory condition or not. Much more work needs to be done before anything concrete can be said about the physiology, the evolution and the adaptive function of limits of entrainment.

Conditions of entrainment may have either transient or lasting effects on the subsequent freerunning period in constant conditions. Such effects are called aftereffects. Exposure to different photoperiods may induce aftereffects, for instance exposure to a short photoperiod may result in a shorter subsequent period, and exposure to the longer photoperiod in a longer subsequent freerunning period. However, the largest aftereffects are seen after exposure to T-cycles: usually short T-cycles causing subsequent shorter periods, and longer T-cycles causing longer freerunning periods.

This phenomenon, although its cause and mechanism are still elusive, was used in some creative experiments. Exposure of two groups of animals to two different T-cycles results in a creation of two colonies of animals with different endogenous periods. Transplantation of candidate pacemaker tissues between the two groups than reveals if the tissue is actually a pacemaker. If the animal's rhythms continue with the period of the host, the transplant is not a pacemaker. If the host animal assumes the period of the donor, the tissue is a pacemaker. This protocol is especially valuable in species in which there are no known naturally occuring period mutations and are not amenable to genetic engineering. Terry Page used this protocol to uncover the pacemaking tissues in the cockroach. More recently, he used aftereffects (of entrainment to T-cycles) in another creative experiment. He exposed two groups of cockroaches to inhibitors of transcription and translation for several hours. Result: aftereffects were retained. The expectation was that such a treatment would transiently stop the clock, which would then re-start with its own, genetically determined "natural" freerunning period. However, the blocked cells managed, somehow, to "remember" the aftereffects through the duration of the treatment, suggesting that the clock-gene transcription-translation feedback loop is not necessary for determination of the most basic property of the circadian rhythm - its period.

I will return to T-cycles and skeleton photoperiods later, when I discuss photoperiodic phenomena. Let me now turn to a different topic: the parametric and non-parametric effects of light. Parametric effects of light are effects of intensity and wavelength of light on the rhythm. Non-parametric effects of light are efects of timing of onsets and offsets of light-pulses (or longer pulses, e.g., photoperiods).

Exposure to constant bright light will often result in arrhythmicity (at the level of the organism - see this post for evidence that individual pacemaker cells keep cycling in mutual asynchrony). In plants, exposure to constant darkness may result in arrhythmicity, mainly due to the plant's photosynthetic needs.

In nocturnal animals, brighter the constant light, longer the period (tauLL > tau DD). In diurnal animals, the reverse is true (tauLL less than tau DD), though there are many more examples of diurnal than nocturnal animals disobeying this rule (either behaving as nocturnal animals, or ignoring the parametric effects of light entirely). Since a relatively recent ancestor of all mammals was a nocturnal burrowing insectivore-like creature, it is likely that some mammals evolved diurnality comparatively recently and retained a nocturnal response to light intensity (I tried to post the image five times and it just won't "take" - I managed to post it in the Archives, though, so click on this to see it:
This whole phenomenon, often written in shorthand with the two little formulas I wrote in the parentheses, was first discovered by Jurgen Aschoff. In 1960., Colin Pittendrigh suggested that this be called Aschoff's Rule, which everyone in the field accepted. The most prestigious award in chronobiology is called, appropriately, Aschoff's Ruler, an actual classroom ruler with names of past winners inscribed on it. The way the award is given is unusual. There is no nominating committee involved. The recipient of Aschoff's Ruler chooses the next year's recipient. But, the two consecutive winners cannot live on the same continent, nor work on the same model organism, or have ever worked on the same organism in their whole scientific careers, which made it difficult for some people who have studied many species, e.g., Mike Menaker, but he got it somehow (he works on a variety of vertebrates, the previous winner, from Europe, works on fungi and protists, and the subsequent winner, from Japan, was using only rats).

In some organisms, exposure to constant bright light results in a phenomenon called splitting. Two (or more) components of the circadian rhythm start freerunning each with its own endogenous period. Thus, when one inspects the actograph record, the components diverge from each other, cross over each other, or fuse again, and this phenomenon usually repeats over and over again. The observation of splitting in the tree-shrew (Tupaia), and subsequently in some other organisms, was an early suggestion (in the history of the field) that organisms possess more than one clock and that multiple clocks may be organized in more complex circadian systems (see CT 5: Circadian Organization).

Study of parametric effects of light continues, with emphasis on effects of gradual dawn and dusk (as opposed to usual laboratory practice of switching the lights on and off abruptly), as well as the roles of various photopigments (e.g., melanopsin, cryptochrome, rhodopsin, pinopsin etc.) and photosensitive tissues (retina, pineal, deep-brain photoreceptors) in detection of different components of natural light, e.g., its wavelength and intensity, both of which change over the course of the day.

Study of non-parametric effects of light analyzes effects of light-pulses (or photoperiods) on phase of the freerunning rhythm. Onsets and offsets of light pulses usually result in phase-shifting of the rhythm. Analysis of such phase-shifts can teach us about the mechanisms of entrainment to full daily exposures to light and darkness. For instance, the difference between abrupt shifts (the phase-shift is completed in one cycle) and transients (rhythm assumes a new phase after several days of gradual shifting) can be very informative about the underlying physiology.

Non-parametric effects of light, as postulated by Colin Pittendrigh, have been studied more extensively and are much better understood. Parametric effects of light, as proposed by Jurgen Aschoff, are less well understood. The only person who studied and published with both of them, Serge Daan, has attempted in recent years to combine the two approaches. In the next couple of weeks, I intend to write a series of posts about formal analysis of non-parametric effects of light (constructing the Phase-Response Curve), as well as attempts to put together parametric and non-parametric effects (e.g., transient-response curve, tau-response curve, application of limit cycles) and, in addition, the utility of such approaches to the study of biological rhythms. This kind of stuff is pretty hard to grasp and contains some heavy-duty math, so I will try to go slow and make it as simple as possible. Still, you are all probably tired of all this theory by now, so I will take a little detour in the meantime and write the next couple of posts on some real anatomy and physiology of circadian systems in mammals and non-mammalian vertebrates before I come back to the theoretical aspects of chronobiology.

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