Monthly Archives: June 2011

Neurosciences behind Ecstasy

For a long time, I have been a shy person, an introvert (to be exact). I preferred to keep my thoughts to myself and never expressed an opinion on anything!

Then, I slowly developed this whole new image of the “wild child”. Not exactly drugs and booze, just that I am open to talk and experience a whole lot of things that aren’t necessarily conventional. No, I am not talking about sneaking a cigarette or drowning a bottle of Tequila. I am talking about things like expressing my views on any topic that are considered to be taboo in India.

Recently, I was talking to my friends about this blog that I wanted to write. About human sexual activities and love (you can read about love here). Not in the adult film kind of way, but the neurosciences behind it. I know most of you started reading this blog post with a certain image in mind. I won’t be pasting pictures of naked women and men. I think there are enough sites to see that. Here I am going to write about the neurosciences and psychology behind that ultimate experience humans go through – Orgasm.

case study published by a team of Taiwanese neurologists reported a most unusual set of circumstances.

One of their 41 year-old female patients, diagnosed with epilepsy, had a seizure every time she brushed her teeth. Seizures in response to external stimulation are not unusual – flashing lights are a well known source – and other sorts of stimulation are not uncommon triggers. A recent case-report even involved seizures induced by vacuum cleaner use.

So the unusual aspect for the Taiwanese case was not the trigger, but the effect of the seizure. The woman had seizures when she brushed her teeth, and had an orgasm every time she had a seizure, shortly before losing consciousness.

Although probably doing wonders for her dental health, the condition has left neurologists rather puzzled. Because so little is known about sex and the brain, her doctors had very little to go on when they tried to explain what was happening.

Ecstasy? Agony? Euphoria? Surprisingly little is known about what happens in the brain at the very peak of our sexual experience. A Dutch team have done the unthinkable and scanned the brains of men and women during orgasm.

Neuroscientists trying to untangle the riddle of desire and sexual pleasure in the brain have discovered something that turns conventional wisdom on its head. During orgasm, men experience heightened activity in the emotion-processing centres of the brain. But women’s brains, say researchers, are shut down in emotion-processing regions during arousal and orgasm.

Physiologist Dr Gemma O’Brian from the School of Biological, Biomedical and Molecular Sciences at the University of New England also has a keen interest in the neurobiology of the orgasm, as fleeting an experience as it can be sometimes.

Gemma O’Brien: And this is one of the problems with trying to look inside the brain during something like orgasm. Orgasm’s a fairly brief event. We enjoy the response for an extended period of time, the resolution phase, but the actual brain changes are fairly brief so finding a technique that can see what’s happening in the brain.

The whole orgasm process is divided into three stages by Masters and Johnson: stage of arousal plateau, sexual climax and resolution. And it’s the sexual climax part that many people use the word ‘orgasm’ for.

So, is it all chemicals or is it all in the brain?

In men who have a high spinal cord injury may have ongoing capacity to use the reproductive tract so they can manually stimulate or tactilely stimulate to erection and all the way through to ejaculation but not detect anything by brain, not orgasm. They have to actually look or feel by hand to see whether anything happened. But they don’t actually have the sensations of euphoria that come with it.

Both male and female sexual reward releases beta-endorphin (Dictionary of Pharmaceutical Medicine, Springer Vienna, 2009) in the brain, which in experiments caused tremor.

[Looking at the brains of orgasming men using a PET scanner] scientists also saw heightened activity in brain regions involved in memory-related imagery and in vision itself, perhaps because the volunteers used visual imagery to hasten orgasm. The anterior part of the cerebellum also switched into high gear. The cerebellum has long been labeled the coordinator of motor behaviors but has more recently revealed its role in emotional processing. Thus, the cerebellum could be the seat of the emotional components of orgasm in men, perhaps helping to coordinate those emotions with planned behaviors. The amygdala, the brain’s center of vigilance and sometimes fear, showed a decline in activity at ejaculation, meaning, men are oblivious to their surroundings during an orgasm.

To find out whether orgasm looks similar in the female brain, [neuroscientist Gert] Holstege’s team asked the male partners of 12 women to stimulate their partner’s clitoris—the site whose excitation most easily leads to orgasm—until she climaxed, again inside a PET scanner. Not surprisingly, the team reported in 2006, clitoral stimulation by itself led to activation in areas of the brain involved in receiving and perceiving sensory signals from that part of the body and in describing a body sensation—for instance, labeling it “sexual.”

But when a woman reached orgasm, something unexpected happened: much of her brain went silent. Some of the most muted neurons sat in the left lateral orbitofrontal cortex, which may govern self-control over basic desires such as sex. Decreased activity there, the researchers suggest, might correspond to a release of tension and inhibition. The scientists also saw a dip in excitation in the dorsomedial prefrontal cortex, which has an apparent role in moral reasoning and social judgment—a change that may be tied to a suspension of judgment and reflection.

Brain activity fell in the amygdala, too, suggesting a depression of vigilance similar to that seen in men, who generally showed far less deactivation in their brain during orgasm than their female counterparts did. “Fear and anxiety need to be avoided at all costs if a woman wishes to have an orgasm; we knew that, but now we can see it happening in the depths of the brain,” Holstege says. He went so far as to declare at the 2005 meeting of the European Society for Human Reproduction and Development: “At the moment of orgasm, women do not have any emotional feelings.”

You cannot basically conclude that these parts of the brains are shutting down because of the intense experience that the body is going through. It is like a busy road, it maybe because there is a sale in the local supermarket, or there might be a circus performance, or there might be a cat fight going on. Come on, you are interested to see two cats fight viciously right?

Brain scanning just finds associations, but to find out whether an area is causally involved in a particular function or whether it is necessary for the function, research with brain injured patients is one of the most powerful methods.

For example, if you think a brain area is necessary for orgasm, or a certain component of orgasm, a person with damage to that area should not experience what you’ve predicted.

Sexual neuroscience is one of the most under-researched areas in the human sciences. A quick search of PubMed (the international database of medical research) shows that we know more about the neuroscience of hiccups than we do about orgasm.

Part of the problem is practical. fMRI scanners, some of the most useful and popular tools in cognitive neuroscience, involve lying in a tube while scanning takes place and need the head to be completely still. Add the fact that you’re being watched by neuroscientists and none of this makes for relaxed coupling, or even self-stimulation.

So, if you have a way of testing people going through this, then tell me. Maybe I can do some mind boggling errr research. (I solemnly swear I am up to only good)




The Phenotypes of Cancer – Cell Immortalization.

Hello there

Now, as already mentioned before on this blog, and as is well known in the scientific literature, cell immortalization, also called the development of infinite replicative potential, is one of the hallmarks of cancer

When a line of cells is called ‘immortal’ , it means that it can be grown indefinitely in cell culture as long as nutrition and oxygen is available. In cell lines that are not immortal even if you continue to supply nutrition and a favourable growth environment, cells stop dividing but remain metabolically active, have increased cytoplasm size and basically end up looking like fried eggs. We call such cells senescent

Cancer cells, or at least the subset that is capable of giving rise to tumours, don’t enter a state of senescence, they continue to divide, i.e, they are immortal.

To be able to understand why some cell lines are immortal and some enter senescence, one needs to be aware of what we call the end replication problem. Now there are caps at the end of chromosomes, made of DNA, that we call telomeres, these telomeres protect the ends of chromosomes from fusing with the ends of other chromosomes, in effect, they serve a kind of protective function.

Telomeres have been labelled using FISH, they are the yellow dots at the ends of chromosomes.

There is a slight kink in DNA replication that we call the end replication problem, the problem is that at one stage of DNA replication, RNA primers, on the lagging strand if I remember correctly will be removed and replaced with DNA by DNA polymerase III provided there is a 3′-OH for it to bind to, but in organisms with a linear genome this is not available, which means that the length of DNA that corresponded to the RNA primer during replication will not be duplicated. This results in telomere shortening.

Once telomeres are so short as to not be able to prevent chromosome to chromosome fusion, cellular crisis occurs. In cells where the pathways of apoptosis (programmed cell death) are fully functional such cells undergo apoptosis, but in cancerous/pre-cancerous cells with impaired apoptosis, they begin to undergo fusion-breakage-fusion cycles, which generates genomic instability and lots and lots of genomic variation. In some cases this leads to a dead end and cells end up with so much genomic instability that they are screwed. But in some cases, the extensive amounts of duplication, amplification and translocation that take place can generate genotypes that are positively selected for, and this can be a key point in the evolution of malignant disease.

Illustration showing how telomere shortening can, conditional to defunct apoptosis induction, trigger the genomic instability needed to evolve variation and reactivate telomerase.

This is often conditional on cells learning to stabilize their newly acquired variant genomes by reactivating pathways of telomere maintenance, of which there are two. One, which is the telomerase pathway, is the one found in a majority of cancer cells, the other is called the ALT pathway (or Alternative Lengthening of Telomeres) pathway.

The telomerase pathway.

Telomerase, which was first discovered in Tetrahymena thermophila(I have no idea how that name came about)
is a multi-unit enzyme that is capable of extending telomeres so that the end replication problem does not result in telomere shortening, it does this by adding the telomere repeat unit sequence to the parent DNA, which is extended before replication.

The way telomerase works has been illustrated below, reference Telomerase and cancer therapeutics, Calvin B. Harley, doi:10.1038/nrc2275

Click on the image to bring a larger version up.

Now telomerase not only stabilizes the genome and enables tumorigenesis to proceed, it also has the effect of suppressing apoptosis (See here for a reference)and upregulating the genes and pathways required for EMT (Epithelial Mesenchymal Transition) which is required for metastasis. Some evidence for this may be found here with particular reference to melanoma.

The ALT Pathway

The Alternative Lengthening of Telomeres pathway involves the use of homologous recombination to maintain telomere length, there are currently several mechanisms and models that have been proposed by which the pathway may function, and insofar this article is concerned those mechanisms are beyond the scope. However, if you so desire you may read an apposite in-depth review here (PDF).

Further reading material

Nature Scitable article on Telomeres of Human Chromosomes

Watch a video on the action of telomerase, here

Read a review of telomeres and telomerase in cancer here

The discovery of telomerase won its discoverers the Nobel Prize, read an illustrated presentation of what they did at the official Nobel Prize website here

You will also be able to find the researchers’ Nobel lectures using the tabs on the same page.

I hope you enjoyed reading this.

– Ankur ‘Exploreable’ Chakravarthy

Will Indian Society finally wake up? – Part Deux.

Warning – reader discretion is advised. Some people might find what is written unpalatable.

Hello there,

A few weeks ago it was an alarming trend towards increasing sex-selective abortions in India, even in sections of the society that were well to do and were educated, that shook me up, and now, in a bizarre turn of events, sex-selective abortion has ended up looking almost palatable in comparison to what has transpired in Indore.

If news reports are to be believed, and from what I know India’s National Committee for the Protection of Child Rights has been taking these reports seriously, the fetish for male children has been taken to a whole new extent in the conservative city of Indore.

Parents have been resorting to changing the gender of their daughters through gender reassignment surgery, also called genitoplasty. Now this is unethical right from the start, reason being that there is tangible harm done to the child, which violates the Hippocratic oath which doctors swear to uphold, but that is only the beginning. There is a very good reason that we don’t allow people to marry children, or give children the right to make their own decisions, or give them the right to vote, or the right to use alcohol, that being that they are incapable of giving informed consent till then; Note the word ‘informed’.

So if there is a medical procedure that is being carried out on people who cannot consent to it and is definitely of no medical benefit, why is it even being allowed in the first place? The only reason I can suspect is that nobody had thought that things could get this weird, now that things have gotten this weird, I suppose it would be great if the legislative bodies in the country acted swiftly to curb the practise; My only fear is that it may send this practise underground, and make it much more difficult to root out.

Right, so what are some of the obvious harms of bringing up a female child as a male child? While I cannot find direct examples of this happening there happens to be one exceptional case in which a male child was brought up as a female child.

David Reimer had a botched circumcision that led to his penis being damaged, his parents had his gender changed (after his testes were removed and what was left of his penis was removed and a hole in his abdomen was constructed to enable urination )under the influence of a controversial psychologist called John Money, who wanted to show that gender identities can be completely learned (i.e, it is purely an externally learned behavioural construct) and brought him up as a girl named Brenda. While John Money was out in the press spouting crap about how the gender reassignment had been “successful” , David Reimer had been undergoing psychological trauma and bouts of severe depression, being unable to adopt a female gender identity, despite being treated with female hormones and having an external female identity imposed.

He then, after bouts of suicidal depression, decided to revert to a male identity at the age of fourteen, and in the years to come he had everything they had done to him to change his gender reassigned. He published a story of his experiences to dissuade other doctors from ever deciding in favour of such a “therapeutic” strategy.

All the years of trauma had taken their toll, though, and with a marriage that began to dissolve he was pushed over the edge and committed suicide.

You can find an account of this case, which was featured on the BBC, here , the BBC documentary described in that page is here.

So, to sum up, that one tragic case should be a warning that should be heeded by parents who are resorting to this kind of absurd practise in Indore, never mind the fact that there is no way doctors should be carrying this procedure out, and never mind the fact that the law needs to be amended to make this illegal since the practise is grossly unethical.

The news report that reported the practise is here and a report of the IPCR deciding to get involved in an investigative capacity is here

I cannot be angry enough with the blinkered muppets who think putting their children through the trauma of gender reassignment without their consent is acceptable, all for the purposes of fulfilling their fetish for a son, if they are so fond of a penis I suggest that they get cadaver dicks grafted onto their heads, it would serve as a mark of identity. Moreover, do these geniuses (yes, that is sarcasm) not realize that females reassigned as males will not be fertile, that they will not produce sperm?

So, what can you do? Speak out, make a stand, oppose misogyny. Remember that having a set of balls or lacking it by birth does not have an impact on how successful, bright, beautiful or wonderful someone might be, also remember that when proponents of such practises see you take notice of the practise but do not speak out, they may see it as tacit endorsement.

I will not shut up, and I don’t think you should either.

– Exploreable.

One of us has just completed another orbit of the Earth round the Sun…

Here is one more general article that is very different in focus from the general trend of articles on the blog; the reason is this, it is Julietooo’s (who is one of the authors on the blog) birthday and I (on behalf of myself and the other authors on the blog) would like to express my thanks to her for her contributions to the blog, all of which have been lucid exhibitions of skeptical analysis pertaining to very relevant social issues and also wish her a happy birthday while doing so.

Her articles have been read more than the articles of any other author, and they have achieved highlights such as being featured on a BBC Buzz page and being linked to blog posts by PZ Myers on Pharyngula, as well as being tweeted to his followers by James Randi, which I think is impressive list for articles on a blog that is still very much in its infancy.

Have a good ‘un, Juliet.


PS – Please keep those articles coming in the future too, that’ll be ideal 😛

PPS – Now I’ve done this orbit round the sun thing too, you may now thank me now for the information in my posts, or alternatively, for curing your insomnia/sleeping difficulties.

– Exploreable.

A sad sad world

This is my 8th attempt at writing today’s article. I must have written almost 5000 words before I restarted my computer to write again from scratch. Every single time I thought I had written enough, electricity flickers (Monsoon time, I can’t help it) in my home and my computer shuts down without me saving the article. I have written so many versions of the same topic because I cannot remember how I introduced the topic to you all. It is quite depressing really. Ahhh!! There it is: my opening. I’m going to talk about a touchy subject – depression.

I’d appreciate it if people took an open mind to what I’m saying, rather than defensively saying ‘I had depression, it is not like that and you don’t know what the hell you are talking about’. I’m not claiming to be a saviour or guru; I’m just writing my opinion based on my personal experiences.

If somebody greets you, you always greet them back with a positive message. Fine, good, great, awesome etc, even if you aren’t. Even if you are sad, depressed, unhappy, in pain, you never let it through and usually try to hide it. So, I thought I will write something about depression and sadness. It is important to know the reason for such things and ways of overcoming it. Did you know there are genes associated with depression? I will tell you more about finding “the gene” later on. First, we will see some of the reasons and factors pushing us towards depression.

Society today through the use of mass media especially TV, movies and magazines gives the impression to young people (more so girls but males as well), that life is going to be one big picnic, you are going to find the partner of your dreams, you are going to be the coolest person around at school, basically that life is going to be one big fairytale.

Now when people reach the mid-teenage years, they begin to discover that the world isn’t everything it’s made out to be. Their parents are just people with the same faults and inconsistencies as anyone else, with the ability to hurt them just the same as anyone else. They read magazines and find that they are not as attractive as the models they read about, begin to discover that the guy of their dreams is possibly not going to ride in and sweep them off their feet (The Twilight guy, whatshisface? Robert Pattinson? Tall, dark, handsome and a rich man), people in their lives are going to do things that upset them, and their grand fairytale plan for life isn’t going to fall into their arms. It isn’t just body issues.You can read more about the body issues here

I think when people begin to realise that the real world is a very different place than what they have been led to believe. Some people are brought up thinking that the world owes them happiness. That their family/friends/teachers are responsible for them feeling bad, and they get stuck in a rut which leads them to be sad about the situation and frustrated at their helplessness.

Recently, an article was published in the Guardian which claimed that depression can be good for you! Here is an extract from that article. I don’t know if it is true, but it sure gives something to think about.

Dr Paul Keedwell, an expert on mood disorders at the Institute of Psychiatry in London, has written how Sadness Survived in order to understand why something that causes so much pain and disability has withstood evolutionary changes and still occurs so commonly. ‘We see it as a defect – often patients see themselves as broken in some way – whereas I think of it as a defence mechanism. It has simply adapted in the human species to actually give us some long-term benefits.

‘Essentially, depression can give us new and quite radical insights – it can give us a way of responding effectively to challenges we have in life. In its severe form it is terrible and life-threatening, but for many it is a short-term painful episode that can take you out of a stressful situation for a while. It can help people to find a new way of coping with events or your situation – and give you a new perspective, as well as making you more realistic about your aims.’

Keedwell says there is good evidence from long-term studies, particularly a recently published population survey of Dutch adults, to show that, after their depression, many patients seem to be able to cope better with challenges. ‘For most, their vitality, their social interaction and their general health actually improved on recovery – and so did their work performance. I know from patients that it can also make you more realistic in your outlook; you develop more empathy to those around you.’

Going deeper into depression:

Much of what we know about the genetic influence of clinical depression is based upon research that has been done with identical twins. Identical twins are very helpful to researchers since they both have the exact same genetic code. It has been found that when one identical twin becomes depressed the other will also develop clinical depression approximately 76% of the time. When identical twins are raised apart from each other, they will both become depressed about 67% of the time. Because both twins become depressed at such a high rate, the implication is that there is a strong genetic influence. If it happened that when one twin becomes clinically depressed the other always develops depression, then clinical depression would likely be entirely genetic. However because the rate of both identical twins developing depression is not closer to 100% this tells us that there are other things that influence a person’s vulnerability to depression. These may include environmental factors such as childhood experiences, current stressors, traumatic events, exposure to substances, medical illnesses, etc.

How people process positive and negative stimuli is central to theories of emotion, and may be the key component in vulnerability factors governing risk for depression and anxiety. Depression and anxiety are commonly experienced in the general population and may significantly impair psychosocial function. In their extreme form these negative affective states develop into clinical depression and anxiety – the most commonly experienced psychiatric disorders today. While these disorders are often characterised as distinct phenomena, they co-occur in up to half the cases with either disorder. Here is an article to read if you are interested in knowing the neurosciences behind depression.

How to overcome it?


Here is a cycle that might give you an idea what is happening during depression. I forgot where I got this article (Remember the 8 power cuts I had to deal with), so I am sorry I cannot refer this properly, but anyway, it gives a good picture about depression and the “escape route”.

While sadness will always be part of the human condition, hopefully in the future we will be able to lessen or eradicate the more severe mood disorders from the world to the benefit of all of us. This can be done by doing research in this progress. And for that, the government and funding bodies have to provide money for the researchers. A long process and umpteen number of convoluted bureaucracy to deal with. It is quite depressing, really.

Of Airplanes and Stuff – Basic Physical Principles.

Hello there,

Airplanes have been an object of fascination from childhood for me, and since I’m extremely bored at the moment with quite some time to kill, I decided to write a little introduction to how airplanes work and examine the physics involved.

The behaviour of air is treated as part of fluid dynamics in Physics, and the explanations that I will write in this post can be visualized with air as a fluid. The dynamics of airplane flight can be explained in the context of four different forces or factors.

To achieve flight, airplanes must defeat gravity and their weight, and they do this through lift, to move forward and generate lift in the process, they need to overcome air resistance (called drag) and they do this through thrust.

Forces acting on a plane.

I will now go on to describe how lift and thrust are produced.

Aerodynamic Lift.

Lift is generated by the way aircraft wings interact with air. Before moving on, please do remember that aircraft wings can generate lift only when moving forward (i.e, there is air flowing over and under the wing at high velocity). Aircraft wings, which we shall call airfoils from now, have a flat surface on the bottom and a curved surface on the top. The way these surfaces interact with the air of the atmosphere is governed by Bernoulli’s principle, air flowing over the wing does so faster, and does so with increased kinetic energy, which in turn creates a low pressure area above the wing, enabling the relatively higher-pressure air under the wing to lift it into the low pressure area above.

Lift and Bernoulli's principle

The reason that the speed of air flowing over the curved surface is greater is the increased distance air has to flow over to cross the wing.

So that does it for lift.


Thrust is required to propel airplanes forward such that their wings are able to generate the required lift to keep them airborne, thrust is produced either through propellers or through jet engines, the former relying on manipulating airflow and pressure differentials and the latter relying on Newton’s third law of motion.

Propellers and airflow.

The blades of a propeller are like tiny wings, but they are oriented at angles that make forward movement, as opposed to upwards movement, possible.

A schematic diagram of a generalized jet engine.

Of Pitch, Roll and Yaw.

Now lift and thrust per se are not sufficient to account for everything that airplanes need to do in flight, including moving from side to side, up and down, and left to right. Since the flight of airplanes is three dimensional, we need three terms to describe these movements.

Pitch is when the airplane is pointed up or down, roll is when it rolls to the left or right (obviously) and yaw is when it is re-oriented to the left or right. See the image below if you have trouble grasping it.

Pitch, Roll and Yaw

These movements are executed by utilizing airflow and Bernoulli’s theorem again, through the use of distinctive control surfaces that are found on airplane wings, stabilizers and tails. The surfaces that control rolling are called ailerons and are found on the wings in most conventional aircraft designs. The surfaces that control pitch are called elevators and are found on the tailplane or in the form of canards in front of the wing.
The surface(s) that control yaw is/are called the rudder and these too are found on the tailplane.

I will blog about the nuances and the intricacies of aircraft parts and systems and control surfaces and aerodynamics and so on in the future, but this is it for this post. Thanks for reading.

– Ankur.

Paper Review – Disrupting Circadian Homeostasis of Sympathetic Signaling Promotes Tumor Development in Mice

Hello there,

This paper was a bit shocking when it first came out, and it is a bit complicated, but I think it is worth reviewing because it is immensely interesting and raises profound questions about the link between various environmental factors and behaviours with tumour progression.

The paper in question is “Disrupting Circadian Homeostasis of Sympathetic Signaling Promotes Tumor Development in Mice
Susie Lee et al” You may duly retrieve the full paper here, which you will actually need to do since I will be leaving the reading of some parts to you to do from the original paper.

Before moving on to pay attention to all the details, it is worth reviewing the abstract, in my opinion. I quote verbatim and then highlight the key implications.


Cell proliferation in all rapidly renewing mammalian tissues follows a circadian rhythm that is often disrupted in advanced-stage tumors. Epidemiologic studies have revealed a clear link between disruption of circadian rhythms and cancer development in humans. Mice lacking the circadian genes Period1 and 2 (Per) or Cryptochrome1 and 2 (Cry) are deficient in cell cycle regulation and Per2 mutant mice are cancer-prone. However, it remains unclear how circadian rhythm in cell proliferation is generated in vivo and why disruption of circadian rhythm may lead to tumorigenesis.

Methodology/Principal Findings

Mice lacking Per1 and 2, Cry1 and 2, or one copy of Bmal1, all show increased spontaneous and radiation-induced tumor development. The neoplastic growth of Per-mutant somatic cells is not controlled cell-autonomously but is dependent upon extracellular mitogenic signals. Among the circadian output pathways, the rhythmic sympathetic signaling plays a key role in the central-peripheral timing mechanism that simultaneously activates the cell cycle clock via AP1-controlled Myc induction and p53 via peripheral clock-controlled ATM activation. Jet-lag promptly desynchronizes the central clock-SNS-peripheral clock axis, abolishes the peripheral clock-dependent ATM activation, and activates myc oncogenic potential, leading to tumor development in the same organ systems in wild-type and circadian gene-mutant mice.

Tumor suppression in vivo is a clock-controlled physiological function. The central circadian clock paces extracellular mitogenic signals that drive peripheral clock-controlled expression of key cell cycle and tumor suppressor genes to generate a circadian rhythm in cell proliferation. Frequent disruption of circadian rhythm is an important tumor promoting factor.

[1] They note that circadian rhythms are disrupted in advanced stage cancers.
[2] They use genes implicated in circadian rhythm maintenance as reference standards in this paper, namely the genes Per1 and Per2 , and also Cry1 and Cry2 , they note that mice carrying mutant versions of these genes are prone to cancer, this already indicates a correlation of statistical significance.

If you go through the introduction of the full paper, you will come to a brief understanding of how the Circadian rhythm is maintained, they note that there is a peripheral clock that alone cannot regulate the circadian rhythm of cell proliferation due to it being based on external mitogenic signals, they then postulate that a central circadian clock is involved to account for this extraneous factor, and this takes the form of a molecular clock in which some of the genes they have mentioned above play an active role. The presence of such a system, the authors note, entails some of the following…

The molecular clock regulates clock-controlled genes (CCGs) to control tissue/organ function. Most CCGs follow tissue-specific expression patterns. Only a small group of CCGs, which include key cell cycle regulators and tumor suppressors, are expressed in all tissues studied. Such circadian control leads to the coupling of cell proliferation with key tissue functions in vivo [19], [20], [21], [22], [23], [24]. Disruption of circadian rhythm in cell proliferation is frequently associated with tumor development and progression in mammals [4], [5], [12], [25], [26], [27], [28].

Both positive and negative loops of the molecular clock are involved in cell cycle control. For example, BMAL1 suppresses proto-oncogene c-myc but stimulates the tumor suppressor Wee1 [19], [22], [29], CRY2 indirectly regulates the intra S-check point [30], [31], and PER1 directly interacts with ATM in response to γ-radiation in vitro [32]. In mice, mutation in Per2 leads to deregulation of DNA-damage response and increased neoplastic growth [19], [24], [29]. In humans, deregulation or polymorphism of Per1, Per2, Cry2, Npas2 and Clock is associated with acute myelogenous leukemia, hepatocellular carcinoma, breast, lung, endometrial and pancreatic cancers, and non-Hodgkin’s lymphoma [12], [33], [34], [35], [36], [37], [38], [39], [40], [41].

As already mentioned above, they develop a hypothesis concerning such a synchronization while also stating that such a thing cannot be reduced to peripheral mechanisms alone. They note that this is because at least some known mitogenic cues (signals that tell cells to divide) are external,and in the G1 phase of the cell cycle, it is completely externally controlled (I’ve written a review on the cell cycle on this blog before, you may find it useful to refer to it at this juncture) which means that the internal, peripheral clocks of individual cells and tissues cannot account for these.

Along with references, they present knowledge of the fact that mitogen mediated cellular replication is synchronized with the activity of tumour suppressors, this led them to investigate one possible mechanism of circadian rhythm control through such synchronization by means of the sympathetic nervous system.

At this juncture, I will leave the discerning reader an opportunity to read the rest of that particular section elaborating why such a desynchronization (which upsets what we call an axis) should lead to problems regulating the cell cycle (which is one of the hallmarks of cancer)

The way the authors tested their hypothesis is the next item up for discussion.

To quote

We found that when kept in 24 hour alternating light-dark conditions (24hr LD cycles), mice deficient in Bmal1 (Bmal1+/−), Cry1 and Cry2 (Cry1−/−;Cry2−/−), Per1 and Per2 (Per1−/−;Per2m/m) or Per2 alone (Per2−/−) were all cancer-prone. About 10–15% of Bmal1−/− mice also showed hyperplasia of salivary glands in spite of a significant reduction in the size of other major organ systems due to aggressive aging [49]. Bmal1+/−, Cry- and Per-mutant mice all showed increased risk of ulcerative dermatitis and hyperplasia in the salivary gland, preputial gland, liver and uterus as well as spontaneous lymphoma, liver and ovarian tumor development, although spontaneous tumors in Cry-mutants were mostly identified after 50 weeks of age, later than that of Per1−/−;Per2m/m and Per2−/− mice

You may ignore the allelic notation at this point, for the formatting is screwed due to the act of having to copy it in, but they noticed that mice with mutations in critical circadian rhythm genes were prone to cancer, thus establishing a correlation. This was followed up by an insight they derived through another cool experimental trick.

A sublethal dose of γ-Radiation induced premature aging on the external appearance of all circadian gene-mutant mouse models studied and further increased incidence of tumor and hyperplasia as well as ulcerative dermatitis in Bmal1+/−, Per- and Cry-mutant mice (Fig. 1b, Table 1 and Fig. S1b). About 8% of irradiated Bmal1−/− mice also developed lymphoma despite an average lifespan of 27 weeks due to a further accelerated rate of aging (Fig. 1c and Table 1). Irradiated Bmal1+/− mice showed a similar rate of tumor development as did irradiated Per2−/− mice (Fig. 1d–e and Table 1). Since all circadian gene-mutant mouse models show increased sensitivity to γ-radiation, we conclude that the molecular clock functions in tumor suppression in vivo.

They used increased sensitivity of said mice to gamma radiation to arrive at the conclusion that tumour suppression was associated with the circadian rhythm.

They then tested what would happen if one were to alter the external visual cues that drive the circadian rhythm (there is a new paper out on PLoS Computational Biology on a mathematical model that explains how such a system works in a plant, but that is beside the point at the moment, so let us carry on), they did this by simulating jet lag.

I quote the relevant section below.

We then examined the role of the central clock in tumor suppression by studying the effects of jet-lag (an 8hr phase-advance followed by an 8hr phase-delay in the onset of the light period every 3 days) on tumor development in mice. We found that jet-lag further increased and hastened tumor development in wt, Cry- and Per-mutant mice and induced pancreatic, kidney and intestinal tumors in mutant mice. However, jet-lag did not significantly change the overall survival and tumor development of irradiated Bmal1−/− mice that were deficient in responding to circadian light cues in the central clock (Table 1, Fig. 2a, Fig. S1c and data not shown) [50]. Jet-lag also significantly changed tumor spectrum and induced osteosarcoma, liver and ovarian tumors, hyperplasia of the salivary gland, liver and uterus as well as severe seminal vesicle enlargement in wt mice (Table 1. Fig. 2b–g, Fig. S1d–l and data not shown). In addition, although when kept 24hr LD cycles, female circadian gene-mutant mice showed an earlier onset and a higher tumor incidence compared to male mutant mice, we did not find a significant gender difference in total tumor incidence and the time of tumor onset among irradiated and jet-lagged male and female mutant mice (data not shown).

They found screwing up the rhythm further by upsetting the cues the genes were linked to hastened tumour development, and this also altered the spectrum of the resulting tumours. They noticed that changing these cues in mice which had genes that could respond to them had an effect but those mutants which did not respond to cues experienced no difference as compared to the first dataset.

Disruption of Circadian Rhythm Promotes Tumor Development in Wild-type Mice. (a) The Kaplan-Meier survival curves of wt, Cry1−/−;Cry2−/−, Per1−/−;Per2m/m and Bmal1−/− mice (−IR: untreated, +IR: irradiated, +IR/Shift: irradiated and jet-lagged, p1: untreated wt vs. untreated mutant mice, p2: untreated wt mice vs. irradiated mice, p3: untreated wt mice vs. irradiated/jet-lagged mice, and p4: untreated vs. irradiated Bmal1−/− mice). Median survival times in weeks (95% CI) are 79.7 weeks (79.2–80.1) for untreated, 78.6 weeks (77.5–79.7) for irradiated and 67.9 weeks (63.3–72.5) for irradiated/jet-lagged wt mice, 76.9 weeks (73.9–80.0) for untreated, 69.3 weeks (64.4–74.2) for irradiated and 54.9 weeks (47.8–62.0) for irradiated/jet-lagged Cry1−/−;Cry2−/− mice, 74.8 weeks (71.8–77.8) for untreated, 67.1 weeks (62.5–71.7) for irradiated and 56.1 weeks (51.0–61.2) for irradiated/jet-lagged Per1−/−;Per2m/m mice, and 35.5 weeks (30.73–40.1) for untreated, 27.3 weeks (23.3–31.4) for irradiated and 28.5 weeks (24.4–32.5) for irradiated/jet-lagged Bmal1−/− mice. Representative pictures of (b) lymphomas in the salivary glands of irradiated/jet-lagged Bmal1−/−, Bmal1+/−, Cry1−/−;Cry2−/−, Per2−/−, Per1−/−;Per2m/m and wt (Per1+/+;Per2+/+) mice, (c) hepatocellular carcinomas in irradiated/jet-lagged Bmal1+/−, Cry1−/−;Cry2−/−, Per1−/−;Per2m/m, Per2−/− and wt (Bmal1+/+ and Per1+/+;Per2+/+) mice, (d) ovarian granulosa cell tumors in irradiated/jet-lagged Cry1−/−;Cry2−/−, Per1−/−;Per2m/m, Per2−/− and wt (Cry1+/+;Cry2+/+) mice, (e) osteosarcoma growing out from the spine into the chest cavity of an irradiated/jet-lagged wt (Per1+/+;Per2+/+) mouse and on the back of an irradiated/jet-lagged Per2−/− mouse, (f) severe cystic hyperplasia of the uterus in irradiated/jet-lagged Cry1−/−;Cry2−/−, Per1−/−;Per2m/m and wt (Per1+/+;Per2+/+) mice, and (g) seminal vesicles from an untreated 60-week old wt (Per1+/+;Per2+/+) mouse and age-matched irradiated/jet-lagged Cry1−/−;Cry2−/− and Per1−/−;Per2m/m mice.

So now we have

[1] Mutant circadian genes —-> increased incidence of cancer relative to fully functional circadian genes.
[2] Mutant circadian genes that respond to external cues + radically altered cues —-> higher incidence than [1]
[3] Mutant genes that don’t respond to external cues + radically altered cues —–> incidence similar to case [1]

Then, in a section I will leave to readers again, they established through the occurrence of renal failure when such deviations occured, using the fact that renal failure is strongly indicative of sympathetic nervous system (SNS) dysfunction, that said time cues must involve the SNS.

They then looked for evidence that the SNS could rhythmically be associated with regulating gene expression. They used Ucp1 mRNA levels as a marker for gene expression, they noted that said mRNA is produced in two peaks and one of them doesn’t vary regardless of whether circadian genes are mutated or not, and the other does, this led them to recognize the fact that the ZT10 peak, as they name it, is controlled by collaboration between both clocks (central and peripheral) while ZT22 is not.

(a) Northern blot of Ucp1 mRNA expression in wt and Per1−/−;Per2m/m BAT in 24hr LD cycles. (b) A summary of three independent Northern blot analyses described in (a) (±SEM). (c) Ucp1 mRNA expression in wt and Per1−/−;Per2m/m BAT in 24hr DD cycles. (d) A summary of three independent Northern blot analyses described in (c) (±SEM). (e) Per2 and Bmal1 expression in wt and Per1−/−;Per2m/m BAT in 24hr LD cycles. Summaries of (f) Per2 and (g) Bmal1 mRNA expression in 24hr LD cycles from three independent experiments (±SEM). (h) Per2, Bmal1 and Ucp1 mRNA expression in BAT from untreated (Control) wt mice and wt mice treated with one cycle of jet-lag (Shift). (i) A summary of three independent Northern blot analyses described in (h) (±SEM). (j) Ucp1 mRNA expression in BAT from age-matched control wt mice and wt mice treated with 10 months of chronic jet-lag. (k) A summary of Ucp1 mRNA expression from three independent Northern blot analyses described in (j). doi:10.1371/journal.pone.0010995.g004

They then repeated this marker associated study with jet lag simulation thrown into the mix,they noted that either the collaboration between the central and peripheral clocks is disrupted or the latter is screwed permanently. We now have evidence that Circadian rhythm disruption, through the SNS, can affect gene expression, but the hypothesis necessitates that tumour suppression be of special importance, how did they solve this problem?

Firstly, they demonstrated that tampering with receptors involved in extracellular mitogenic signalling (i.e growth signals from outside the cell) resulted in varied proliferation, thus establishing that cell cycle progression could be linked to external mitogenic cues. This section I will again leave to the discerning reader. The nature of the agonist used, being linked to the signalling pathways mentioned before, illustrated that the SNS is a source of, through those pathways , mitogenic signals.

We now have evidence that the SNS is associated with cell cycle control.

Next, using the same agonist and the mechanism to study the effect of activation of said pathways on cellular function, they investigated the functioning of p53 which can be regarded as the master guardian of the cell, and this is a tumour suppressor. They note…

Since p53 plays a key role in preventing Myc oncogenic activation [48], we studied whether iso also induces p53 expression in preosteoblasts. We found that p53 was induced by iso with kinetics similar to AP1 transcription factors in wt osteoblasts. However, iso-treated Per1−/−;Per2m/m osteoblasts showed AP1 overexpression in the absence of p53 induction (Fig. 6a). The expression of p53 is mainly controlled by its interaction with the E3 ubiquitin ligase MDM2 in vivo [56], [57]. Thus, we examined MDM2 expression in iso-treated preosteoblasts. We found that MDM2 was suppressed by iso with the same kinetics as p53 induction in wt osteoblasts, but remained high in Per1−/−;Per2m/m osteoblasts (Fig. 6a). The MDM2-p53 interaction is best studied in γ-radiation response, which activates protein kinase ATM that phosphorylates p53 at Ser18 (S18) and MDM2 at Ser395 (S395) in mice. The phosphorylation at these two sites blocks MDM2-p53 interaction, leading to MDM2 autoubiquitination and p53 induction [58]. Since we used an anti-MDM2 2A10 antibody raised against a MDM2 C-terminal region containing the S395 residue, the interaction of 2A10 with MDM2 could be blocked by MDM2 S395 phosphorylation [58]. Thus, we studied MDM2 and p53 expression in iso-treated preosteoblasts using an anti-p53 S18 antibody and an anti-MDM2 AB4 antibody that interacts with MDM2 at the N-terminal region. We found that these two antibodies detected a similar rate of p53 induction and MDM2 degradation in wt osteoblasts as shown by the p53 PAb421 and MDM2 2A10 antibodies but failed to detect p53 S18 induction and MDM2 decrease in Per1−/−;Per2m/m osteoblasts (Fig. 6b). We then studied p53 induction in iso-treated wt and Atm−/− preosteoblasts. We found that in wt osteoblasts, ATM was activated by iso, as shown by ATM S1981 phosphorylation [59], in an iso dose-dependent manner and that the duration and the levels of ATM activation correlated with the level of p53 S18 phosphorylation and total p53 accumulation. In contrast, Atm−/− osteoblasts that lacked p53 S18 phosphorylation failed to show p53 induction by iso (Fig. 6c–d). Together, our findings indicate that the SNS activates p53 via ATM in a peripheral clock-dependent manner.

They established that the SNS can activate p53 through a mechanism that requires the peripheral clock too.

So now, circadian rhythm disruption, which can also involve the SNS, especially when jet lag et cetera is present, through the SNS can screw up cell cycle control, firstly and also affect p53 function, which is critical to tumour suppression, we have seen evidence of how this happens and through what components it may occur as well.
It therefore enables aberrant cells to proceed to full blown cancer with much more ease than normal.

There endeth a very brief exposition of what is a content heavy paper, which of course can always be found using the link at the top. It is a brilliant paper, absolutely cutting edge and insightful and I think you will be immensely satisfied if you excercise the due diligence required to assimilate the original paper. My review was just an effort at facilitating something like that.

Moral of the story – sleep regularly, and too much jet-lag is bad for you if you want to keep your tumour suppression systems running smoothly.