Pharmacology

Forced to suffer for science: From animal cruelty and experimental inefficiency to a change of perspective.

Posted on by Iasmina Hornoiu

We, as scientists, have become desensitised to the pain, the distress and the physical and emotional damage that we inflict on laboratory animals. So much so, that we constantly find justifications for our cruel experiments in the goal of finding cures for the illnesses of our conspecifics, and in the rules and regulations that authorise these heartless procedures.

Despite ongoing widespread use of animal models in research, recently there has been extensive criticism on the state of drug development in psychiatry, calling for a switch from rodent behavioral pharmacology to mechanistic studies in cellular systems. In a recent paper, Heilig and colleagues argue that:

Overall, neuroscience has simply had very little impact on clinical alcoholism treatment. The situation is representative of a broader translational crisis in psychiatric neuroscience. Because translational failures in this area have been the rule rather than the exception, pharmaceutical industry has largely retracted from efforts to develop novel psychiatric medication. As a result, the utility of animal models in research on psychiatric disorders, including addiction, is also being questioned.

Heilig et al. (2019)

Caricature Cruelty

Several experimental paradigms employed by labs all over the world, for elucidating the mechanisms of mental disorders and for the development of new psychiatric drugs, consist of procedures that innevitably cause suffering to the experimental animals. From learned helplessness paradigms (forced swim and tail suspension), intended to model the symptoms of depression in humans, to neuropathic pain models, which involve nerve operations to induce chronic pain in rats or mice, as well as fear conditioning experiments, consisting of series of electric shocks on consecutive days, large numbers of laboratory animals across the globe are subjected to procedures at the end of which they are euthanized for histological analyses.

The two videos below illustrate two paradigms for learned helplessness in rodents – forced swim and tail suspension, respectively. Even for those unfamiliar with these methods, it is not hard to notice the amount of distress and fear the animals are forced to go through.

Another example, otherwise claimed to be minimally invasive and highly relevant for medication testing (Meinhardt and Sommer, 2015), is the post-dependent animal model, a model for medication development in alcoholism. It involves inducing dependence through repeated intermittent cycles of alcohol vapour exposure. In other words, rodents (usually, rats) are exposed every day, for several weeks or months, to cycles of intoxication with alcohol vapours, alternating with withdrawal, which ultimately result in compulsive alcohol intake, excessive alcohol seeking, hypersensitivity to stress as well as the development of an alcohol withdrawal syndrome, which better resemble human alcoholism.

Rats usually undergo 5 cycles of 14 (sometimes, 16) hours of forced exposure to alcohol vapours, separated by 10-hour periods of withdrawal and an additional 58 hours at the end of each weekly cycle. These cycles take place over many weeks. As a result of severe alcohol intoxication, some rats die during the experiment. At the end of the last alcohol exposure, the rats that have survived are decapitated.

The sardonically humorous caricatures below, selected from (Meinhardt and Sommer, 2015), not only illustrate the procedure, but are at the same time indicative of a certain emotional detachement these scientists have developed from the rats they used in their experiments.

Mainhardt & Sommer (2015)

“Unavoidable” Suffering

Granted, there have been attempts at reducing the suffering of these poor animals. The three Rs – Replacement, Reduction and Refinement – reflect the scope to encourage alternatives to animal testing, as well as improving animal welfare in experiments where the use of animals is unavoidable. The 3Rs have been incorporated into the legislation governing animal use in many countries, in order to ensure that the use of animals in testing is as ethical as possible.

And yet, with paradigms such as forced swimming test, also known as the behavioural despair test, or the tail suspension test ( where the rodent is hanging from its tail upside down and is unable to touch the walls of the compartment), it is clear that there is a big discrepancy between what could be done and what is actually being done. We could move away from these cruel practices, which have been demonstrated to be misleading and offer little understanding on the mechanisms behind psychiatric conditions, and, instead, resort to alternative strategies, which have the potential to set research on a path of true breakthroughs in psychiatry (as it is being presented in a later section). However, most papers focused on schizophrenia, anxiety, depression, Alzheimer’s disease, addiction etc. rely on experiments which would make the skin of the more sensitive of us crawl, and those with a tougher skin reconsider their academic career (such as switching to cognitive neuroscience and human-based studies only, in my case).

It is also important to remember that, not only the procedures themselves cause pain and suffering to the experimental animals, but often times the side-effects of the medications being tested on them and the behavioral tests they are being used in result in long-term health consequences – for instance, postdependent alcoholic rats end up developing peripheral secondary osteoporosis.

When suffering exceeds a certain limit, the animals are usually euthanized. What a great life these creatures must have, given that one of the best solutions to end their pain is premature death…

Rats empathise with other helpless rats

Although we all know that “animals have feelings too”, we are still far from understanding to what extent animals actually feel. In humans, for instance, pain and consciousness are tightly linked. We do not yet know which animals have consciousness and what (if anything) that consciousness might be like.

That being said, a study from 2011 demonstrated that rats exhibit emotional responses and empathy. In their experiment, Bartal and colleagues showed that when a free rat occasionally heard distress calls from another rat trapped in a cage, it learned to open the cage and released the other animal even in the absence of a payoff reunion with it. The free rat would even save a chocolate chip for the captive.


The presence of a rat trapped in a restrainer elicits focused activity from his cagemate, leading eventually to door-opening and consequent liberation of the trapped rat. (Science/AAAS).

This experiment clearly shows that rats, and possibly other animals as well, are capable of complex emotional experiences, previously only attributed to humans (more studies should be done to investigate this fascinating and important topic). Alas, in the absence of a deep understanding of the animal psyche, and moreover, with clear indications that animals possess the capacity to feel almost to the same extent as us humans do, we still continue to abuse them in our cruel experiments.

The issues with animal models

Valid disease models do not exist for psychiatric disorders.

Hyman (2012)

On the rodent models based on learned helplessness, Hyman went on to argue that:

Forced-swim and tail suspension tests do not even model the therapeutic action of antidepressants, because in those rodent screens a single dose of antidepressant is active, whereas in dependent patients, antidepressant drugs require weeks of administration to exert a therapeutic effect.

Hyman (2012)

In fact, given that most psychiatric diseases are heterogenous and polygenic, often times animal behavioral models have turned out to be misleading. Shockingly, only 8% of the CNS drug candidates developed between 1993 and 2004, which reached initial human testing, were approved to be used as medication. The main drawbacks of these drugs were the toxicity discovered in late-stage clinical trials, along with the inability to demonstrate efficacy. Not to mention the serious side effects these drugs produce in humans, such as weight gain and metabolic derrangements.

Animal models, albeit useful for some translational investigations and for basic studies in neuroscience, present various limitations:

  • Lack of molecular and neural circuit-based characteristics, which are required for molecular studies of psychiatric diseases.
  • The construction of transgenic mice is too slow and expensive.
  • Regarding non-human primates, the challenges involve cost, less well-developed technologies as well as ethical barriers.
  • When it comes to invertebrate models or zebrafish (extensively used in translational research), evolutionary distance poses huge obstacles in translational psychiatry, although they could be useful in the initial molecular investigations of the functions of risk alleles emerging from genetic studies.

Given the above-mentioned drawbacks of relying on animal models to develop psychiatric treatments, major pharmaceutical companies have already decided to move away from these old-fashioned approaches. Now, the question remains, what is there to do in the future?

Adopting new strategies in psychiatric research

Science needs to move forward and find better methods to study the highly complex mechanisms underlying psychiatric diseases, in order to allow for truly efficient drugs and therapies to be developed. As mentioned earlier, animal-based studies have more often than not failed to identify pharmaceutical compounds with positive outcomes in humans.

Over the last half-century, despite the identification of several antipsychotic and antidepressant drugs, alongside the discovery of various neurotransmitters, receptors and transporters involved in mental illnesses, objective diagnostic scans are scarce, and, surprisingly, only a handful of validated molecular targets have been established.

Luckily for us, there are several alternative solutions, which are already being seriously considered by various laboratories and drug companies, as listed below:

  • DNA sequencing, which is nowadays much cheaper than it used to be (by 1 million-fold), makes it possible to analyse large number of subjects, in the attempt to identify genes involved in the heterogenous, polygenic psychiatric disorders.
  • Large scale studies of gene function, epigenetics, transcriptomics and proteomics would contribute to the understanding of pathogenesis.
  • Optogenetics, a technology with increasing popularity in neurobiology, allows researchers to activate or inhibit single cell types, thus detecting which circuits are specific to certain disorders.
  • Human neurones derived directly from skin fibroblasts and blood cells in vitro, or generated from human embryonic stem cells (hESCs) or induced pluripotent stem cells (iPSCs) in vitro.
  • These above-mentioned tools can be combined with electrophysiological and neuroimaging data from humans, which can indirectly reveal abnormal functioning of widely distributed circuits.

What psychiatric research needs is to be able to accurately model molecular mechanisms of disease, instead of relying on behavioral results. Since I already mentioned large-scale genetic as well as epigenetic strategies, it is fair to admit that such studies require suitable living systems in which experiments can be conducted (given that the living human brain is not accessible, and that postmortem studies have limitations when it comes to functional analyses). Although, in some circumstances, animal behavioral experiments can help in elucidating treatment options, conclusions ought not to be based on modelling disease symptoms, as these can be misleading and often fail to translate into human psychopathology. Moreover, symptoms change over time and depending on the context, and are based on subjective rating scales, making the comparison between human and animal conditions difficult.

The solution is plain and simple – scientists and pharmaceutical companies must, first of all, unanimously and once and for all come to terms with the fact that the efforts based on cruel animal studies have been of too little avail to justify their continuation. Instead, a new strategy must be incorporated by the scientific community in psychiatric research, which should carry on from cell-based models and established molecular mechanisms to early human trials, skipping the intermediate step of animal behavioral models.

To end on a cheerful note, here is a heartwarming video which proves there is hope that the future could look bright for laboratory animals if people are willing to start making a change:

Special thanks to my mom for insightful comments and for her constant support, and to Gasser Elmissiery for inspiring discussions and for his contribution to creating the featured image.

References

  1. Bartal, I. B.-A., Decety, J., & Mason, P. (2011). Empathy and Pro-Social Behavior in Rats. Science, 334(6061), 1427 LP – 1430. doi:org/10.1126/science.1210789
  2. Haaranen M, Scuppa G, Tambalo S, Järvi V, Bertozzi SM, Armirotti A, Sommer WH, Bifone A, Hyytiä P. (2020). Anterior insula stimulation suppresses appetitive behavior while inducing forebrain activation in alcohol-preferring rats. Transl Psychiatry. 10(1):150. doi: 10.1038/s41398-020-0833-7
  3. Hansson AC, Koopmann A, Uhrig S, Bühler S, Domi E, Kiessling E, Ciccocioppo R, Froemke RC, Grinevich V, Kiefer F, Sommer WH, Vollstädt-Klein S, Spanagel R. (2018). Oxytocin Reduces Alcohol Cue-Reactivity in Alcohol-Dependent Rats and Humans. Neuropsychopharmacology. 43(6):1235-1246. doi: 10.1038/npp.2017.257
  4. Heilig M, Augier E, Pfarr S, Sommer WH. (2019). Developing neuroscience-based treatments for alcohol addiction: A matter of choice? Transl Psychiatry. 9(1):255. doi: 10.1038/s41398-019-0591-6
  5. Hyman SE. (2012). Revolution stalled. Sci Transl Med. 4:155cm11
  6. Knobloch HS, Charlet A, Hoffmann LC, Eliava M, Khrulev S, Cetin AH, Osten P, Schwarz MK, Seeburg PH, Stoop R, Grinevich V. (2012). Evoked axonal oxytocin release in the central amygdala attenuates fear response. Neuron. 73(3):553-66. doi: 10.1016/j.neuron.2011.11.030
  7. Meinhardt MW, Sommer WH. Postdependent state in rats as a model for medication development in alcoholism (2015). Addict Biol. 20(1):1-21. doi: 10.1111/adb.12187
  8. Wahis, J., Kerspern, D., Althammer, F., Baudon, A., Goyon, S., Hagiwara, D., … Charlet, A. (2020). Oxytocin Acts on Astrocytes in the Central Amygdala to Promote a Positive Emotional State. BioRxiv, 2020.02.25.963884. doi:org/10.1101/2020.02.25.963884

Depression and why some of us are SAD

Posted on by Iasmina Hornoiu

I am warning you, this is going to be a long one! But it’s interesting, I promise.

There is a lot of confusion and mixed opinions when it comes to depression. Some people use the term inappropriately, to describe what is in fact grief (the feeling of sadness that humans, and presumably other animals, experience after a loved one has died, for instance), others tend to label depressed individuals as “weak”, “selfish”, “useless”, “cowards” etc.

At the same time, for the past 30 years, there have been extremely important discoveries in the field of affective disorders, which have helped eliminate many misconceptions and laid the foundation for a better understanding of what this set of disorders (affective disorders) are and what is actually happening in the brain of the ones “affected”. Moreover, according to some new theories, depression is in fact an evolutionary advantage in situations such as physical illness and dominance. When the body is sick it needs time and energy in order to recover, so the organism experiences depression in order to avoid activity and focus on recovery; in nature, many animals with a dominant status are forced (by a variety of factors) to occupy a lower hierarchical level, in which case “depressive” behaviours such as avoiding eye contact or sexual contact helps reduce the risk of attack by other dominant, more powerful individuals. There are many theories, as you can see, and this article is meant to present and analyse some of them.

We should start by clarifying a very important aspect: depression is different from grief. While the latter is a normal reaction to some external factor(s) with a negative emotional impact on our day-to-day lives, and dissipates by itself after a certain period of time, depression is a pathological, abnormal condition (either in its own right or as a symptom of other metabolic or neurodegenerative diseases). However, it should be noted, and this is one of the key concepts in understanding depression, that the way individuals interpret and react to various external events, which affect their mood, differs, which means that some individuals have a stringer predisposition to depression than others. Now, why is that? A variety of factors, both genetic and epigenetic (developmental, such as child abuse, neglect) play a role and often act synergistically, but we will deal with them (especially, the genetic factors) a bit later in the article.

Different types of depression

Major depressive disorder, also known as “the classical depression”, which is characterised by insomnia, anorexia and lack of joy and interest in things. At the opposite side of the spectrum, there is atypical depression, which manifests itself through increased sleepiness, weight gain and anxiety. Dysthymia is another form of depression, more difficult to diagnose, due to the fact that it presents itself with mild depressive symptoms. All these types discussed so far have been categorised as monopolar.

Bipolar depression refers to a kind of depression accompanied by periods of mania – manic episodes are characterised by elevated, euphoric mood, impulsiveness, hyperactivity and even psychotic symptoms (hallucinations, delusions). A case described by Dick Swaab in his book “We are our brains – from the womb to Alzheimer’s” portrays a woman, who developed mania following the death of her husband. She would talk and laugh hysterically, call the police in the middle of the night for no reason and eventually began to make up stories about people whom she had never met before, but who she believed were longtime friends of hers. After her manic episodes disappeared as a result of treatment, she developed severe depression. Luckily, her story has a happy ending, as she made a full recovery.

Bipolar depression is also associated with Seasonal Affective Disorder (SAD), characterised by extreme mood seasonal swings. In this article, I have dedicated an entire section to SAD, so I am not going to delve into it for now. Given all these particularities of BD, it is often regarded as a separate disorder (bipolar disorder or manic disorder), rather than another type of depression. As there are so many things to mention about depression, I will leave BD for future article.

Diagnosing depression

In order to be diagnosed with depression, one must have at least one of the two main symptoms: persistent sadness and marked loss of interest, as well as at least five secondary symptoms: disturbed sleep (either increased or decreased), disturbed appetite (increased or decreased), fatigue, poor concentration, feeling of worthlessness and excessive guilt, suicidal thoughts.

Depending on the number of these symptoms, as well as the degree to which they manifest, monopolar depression can be sub-divided into: sub-threshold depression (fewer than five secondary symptoms; no treatment needed), mild depression (fewer than five, but in excess secondary symptoms), moderate depression (more than five, plus functional impairment between mild and severe depression) and severe depression (most of the secondary symptoms and also true psychotic symptoms – yes! they can occur in severe monopolar depression as well, not just BD).

Biochemical pathways and brain systems involved in depression

In Ancient Greece, there was a biochemical theory of depression. It was believed that depression was caused by the failure of liver to eliminate toxic substances from the digested food, resulting in the accumulation of “black bile” (melan means “black” and chole means “bile”, which give the words melancholy). Biochemical theories nowadays have at their core three monoamines, which I am sure you are all familiar with: noradrenaline (a neuromodulator very similar to adrenaline) and serotonin and dopamine.

These two substances have long and diffuse projections throughout the nervous system and in levels lower than otherwise normal, they are said to be involved in affective disorders. For example, drugs such as Reserpine, used to treat the positive symptoms of schizophrenia by depleting dopamine (and also serotonin and noradrenaline) elicited depressive symptoms in schizophrenic patients.

Therapies involving monoamines

The idea is, you want to higher levels of monoamines in order to treat depression. Enzymes involved in the monoamine re-uptake mechanism from the synaptic cleft back into the presynaptic level and enzymes involved in the monoamine metabolism, such as monoamine oxidases (MAO) are the most common targets for the majority of anti-depressants.

  • Selective serotonin re-uptake inhibitors (SSRI) and selective noradrenaline re-uptake inhibitors (SNRI) – Prozac (Fluoxetine), Zoloft (Sertraline), Celexa (Citalopram), Paxil (Paroxetine) block serotonin reuptake and Effexor/Viepax/Trevilor/Lanvexin (Venlafaxine), Cymbalta (Duloxetine) inhibit the noradrenaline reuptake enzymes. For those of you who are currently under this treatment, be careful! Side-effects such as sexual dysfunction, insomnia, increased aggression and self-harm/suicide can occur. Moreover, SSRI are not so effective. They have a very long induction, which means that it takes a long time (2-3 weeks) for the therapeutic effects to start working, during which time there is a high risk of suicide (due to depression). They also have a placebo effect of 50%, which is not necessarily a bad thing as long as it works, but raises the question whether the monoamine hypotheses is really that valid in the case of depression.
  • Tricyclic antidepressants – also block the reuptake mechanism, resulting in more monoamines in the synaptic cleft. Amitril (Amitriptyline), Aventyl/Norpress/Noritren (Nortriptyline) and Tofranil (Imipramine) are a few examples. They are derived from Phenothiazines (such as Chlorpromazine), which are antipsychotic drugs (used to treat schizophrenia). Some of the side-effects are: chronic pain and suicide overdose.
  • MAO inhibitors – Nardil/Nardelzin (Phenelzine), USAN (Thanylcypromine), Marplan/Enerzer (Izocarboxazid) and Amira/Aurorix/Clobemix (Moclobemide) are very effective and widely prescribed for in major depressive disorder, bipolar disorder and anxiety disorder, although the first three pose the high risk of hypertensive crisis and death if the patient is consuming cheese or wine.

The big problem with these drug therapies is dependence – if antidepressants, especially Paroxetine and Venlafaxine are administered for a long period of time and then stopped, the patient is likely to experience Antidepressant discontinuation syndrome, characterised by flu-like symptoms, motor and cognitive disturbances.

Non-drug therapies

An alternative to pharmaceutical treatments is represented by transcranial magnetic stimulation (TSM) of the cortex, electroshock therapy – this is, apparently, very effective, BUT might result in impaired memory – and gene therapies. The latter refers to the insertion, via a vector or a plasmid, of genes that encode neurotransmitter molecules, receptor proteins or neurotrophic and neuroprotective substances. Given that many variations in genes for chemical messengers in the brain are responsible for the predisposition of certain individuals to depression, gene therapies, although still at a developing stage, provide powerful approaches to the treatment of affective disorders.

Over-activation of the stress axis

Another theory for the development of depression, which goes hand-in-hand with the “monoamine hypothesis” is that in depressed individuals there is an exaggerate amount of cortisol (a steroid) in the blood, which can affect the brain. Basically, our brains react to stressful situations by producing some hormones in the hypothalamus and pituitary gland (hypophysis), which eventually result in the production of cortisol. In turn, cortisol acts on these structures to inhibits their activity and, thus, preventing further increases in its level – this is an example of a negative feedback mechanism.

In normal people, a stressful situation will result in increased levels of cortisol, but this steroid will then revert to its normal levels. In depressed individuals, the stress axis (hypothalamus-pituitary-adrenal axis) becomes hyperactive and, as a result, a stressful event will result in the overproduction of cortisol.

In excess, cortisol affects brain structures involved in the control of emotions and fear, such as the cingulate cortex and amygdala (which explains the anxiety symptoms experienced by people suffering from atypical depression) and memory, such as the hippocampus, which explains the cognitive dysfunctions. Moreover, the activity in the prefrontal cortex, which normally inhibits the hypothalamus (overactive in depression) is decreased by cortisol. So, really, it is like a vicious circle.

Why is the stress axis hyperactive in the first place? Possibly due to decreased sensitivity of the cortisol receptors to cortisol, which might be the result of genetic as well as developmental factors (previously mentioned).

Monoamines play a role here, as increased levels of monoamines (by the administration of antidepressants) can determine neurogenesis in the prefrontal cortex and hippocampus, so these areas can function properly again and can, thus, inhibit the hypothalamus, so no longer hyperactivity of the stress axis!

Seasonal affective disorder (SAD)

Although I am planning to write about bipolar disorders in another article, I thought it is worth discussing SAD in this article as well, given that so many people, especially those living in the Northern hemisphere, suffer from it.

In the References section there is a document called “The recent history of seasonal affective disorder (SAD)”, which is a transcript of the 2013 Witness Seminar in London. I highly recommend this reading for two reasons: it is full of remarkable, extremely important information regarding SAD and the participants at this seminar included personalities such as Prof. Josephine Arendt, Prof, Norman Rosenthal, Prof. Alfred Lewy, Prof. Rob Lucas, who are pioneers of the SAD diagnostic criteria and underlying causes (for instance, Rosenthal is the first psychiatrist who diagnosed SAD).

As many of you probably know, and sadly from personal experience, SAD is a seasonal mood change disorder, a type of bipolar disorder, which determines depression during the autumn/winter seasons and hypomania during summer. In order to understand SAD, we must remember a few things about the circadian rhythm, which I have previously discussed in two articles: Why “sleep” and Even flies sleep and learn. In short, we have an internal, genetic “clock” inside our brains (in the Suprachiasmatic nucleus – SCN), which determines the body to function in an approximately 24-hour cycle and which is also entrained by the light-dark cycle. This is not only a circadian (day-night) clock, but also a seasonal clock, which means that changes in the environment (especially light and temperature) across the year entrain this clock and determine physiological and psychological changes in our bodies.

In SAD, there is an abnormal secretion of melatonin (the hormone that triggers sleep, when it is dark outside). Light inhibits this hormone: cells in our retina, which are not coding for visual information, send projections via a distinct pathway than the rods and cones. These cells, containing  the peptide melanOPSIN, project via the retinohypothalamic tract to the SCN, “telling” the brain that it is dark outside, so the brain (SCN) determines the synthesis and release of melatonin from the pineal gland. When there is light outside, the production of melatonin is inhibited. The duration of melatonin secretion is also affected by the circannual changes – long secretion in short days and short in long days. The scientists who took part in the Witness Seminar discovered that melatonine production was increased during the depressive/winter phase and that sunlight decreased its production, thus, alleviating the symptoms of depression in SAD. A note here, sunlight is an effective treatment for SAD, not ordinary room light. This explains why, during winter, when people tend to spend more time indoors, their levels of melatonin increase. The reasons why room light does not inhibit melatonin production are the intensity of light (sunlight is five times more intense than room light) and spectral differences. More about SAD and bipolar disorder in a future article!

I hope this article made sense and that you enjoyed reading it!

References
SAD – Pdf of The Witness Seminar transcript

Beatty, 2000. The Human Brain – Essentials of Behavioural Neuroscience. Sage Publications. Inc., pg.464-471

Dick Swaab, 2014. We are our brains – From the womb to Alzheimer’s. Penguin Books, pp. 112-122

Image by Damaris Pop

Decoding autism

Posted on by Iasmina Hornoiu

About a year ago, I posted an article entitled Autism, which was meant to be more of an introduction into autistic spectrum disorders. Since then, I’ve been meaning to come back to this topic and provide more details about the mechanisms leading to autism, but I knew I need to do some proper research, which my student schedule didn’t really allow at that point.

The reason why I didn’t post any articles in the past three months is mainly my uni dissertation, which took up a lot of time. My chosen topic was Cellular mechanisms of autistic spectrum disorders. This assignment offered me the chance to read a lot of scientific papers and have a far better understanding of autism than I had before. As you probably guessed, this article draws quite a lot on my dissertation.

Some clarifications

When we refer to autism, we must be well aware that this is just an extreme end of the spectrum and that different neurodevelopmental disorders, sharing particular symptoms, are grouped under the term autistic spectrum disorders (ASD). The symptoms that characterise ASD are: impairments in social interaction, communication deficits and repetitive behaviours. Several factors have been linked to ASD, including gene dysregulations, alterations of the immune system and even environmental risk factors.

Discussing all the possible causes of ASD, could probably fit in a book, rather than a blog article, so I will only focus on gene dysregulations. However, if you have any kind of questions, feel free to post them in the comment section and I will try my best to answer them.

About glutamate and one its receptors

In biochemistry there are 20 different amino acids (the building blocks of proteins) and one of them is glutamate. This particular amino acid is very important because, apart from its role in the formation of proteins, it is also the main excitatory neurotransmitter in the brain. This means that glutamate is used to help the neurons communicate with each other and give rise to all sorts of brain activities we know about, including learning and memory.

When two neurons interact at the synapse (the space between the terminals of two interacting neurons), the neurotransmitter is released from the first neuron’s terminal and comes in contact with the second neuron’s terminal. But here’s the trick: in order for the neurotransmitter to have an effect on the second neuron, it has to activate certain structures on its terminal, called receptors. In the case of glutamate, there are three types of receptors, involved in different functions and with different mechanisms. The one we will be focusing on is the type I metabotropic glutamate receptor (mGluR). When this receptor interacts with glutamate, it leads to the translation of specific proteins involved in a process known as long-term depression (LTD), which influences learning and memory. Increased LTD is thought to play a key role in the development of ASD.

The FMRP protein

A few genes have been found to regulate the activity of mGluR and, through it, several cognitive processes. The Fragile X Mental Retardation 1 (FMR1) gene, which codes for the FMRP protein, is one of these genes. It interacts with mGluR-dependent proteins and is thought to regulate synaptic plasticity. During embryonic development, FMRP plays an important role in neural differentiation. Therefore, a mutation in the FMR1 gene leading to the absence of FMRP (a loss-of-function mutation) results in restricted brain development, impaired cognitive functions and autistic symptoms (previously mentioned). This mutation has been found in patients suffering from autism and especially from another brain disease, Fragile X Sydrome, which is the most common monogenic (determined by a mutation in a single gene) cause of autism. The activity of FMRP suppresses mGluR-dependent LTD, by inhibiting the synthesis of proteins involved in this process. Therefore, the absence of FMRP results in LTD, which primarily leads to mental disability.

Neuroligins and Neurexins

These represent transgenic protein families, which mediate synapse maturation in neurons using glutamate. Mutations affecting members of neuroligin and neurexin families have been found to be associated with autistic-like behaviours. The effects of these mutations on the brain are very specific, affecting cells in brain regions involved in learning and memory (CA1 pyramidal cells of the hippocampus, the Purkinje cells of the cerebellum), language (brainstem) and social interaction (somatosensory cortex). In normal situations, neuroligins and neurexins trigger mGluR-induced LTD, but their translation is inhibited by FMRP. The absence of FMRP leads to the loss of this inhibition, which results in mGluR-induced LTD.

Possible therapeutic strategies

Research on the links between mGluR transmission and genes involved in neural development resulted in a variety of therapeutic strategies for ASD. Genetic mGluR reduction and mGluR antagonists (drugs that act on this receptor by preventing glutamate to activate it) are the most common examples of treatments. Potential therapeutic candidates are Fenobam and Lithium, which act as antagonists at mGluR. Administered on animal models and on humans suffering from Fragile X Syndrome, these drugs have resulted in cognitive and behavioural improvements. Although there is hope in treating ASD, there is still a lot of research that needs to be done, especially since even diagnosing different autistic spectrum disorders is still a challenging task.

I hope this article gave you a little more insight into the mechanisms underlying autism and that you enjoyed reading it. As I mentioned above, any questions about this topic are welcomed.

References:

Baudouin, S. J. (2014). Heterogeneity and convergence: the synaptic pathophysiology of autism. European Journal of Neuroscience, 39(7), 1107-1113.

Berry-Kravis, E., Hessl, D., Coffey, S., Hervey, C., Schneider, A., Yuhas, J., Hutchison, J., Snape, M., Tranfaglia, M., Nguyen, D. V. & Hagerman, R. (2009). A pilot open label, single dose trial of fenobam in adults with fragile X syndrome. Journal of Medical Genetics, 46(4), 266-271.

Espinosa, F., Xuan, Z., Liu, S. & Powell, C. M. (2015). Neuroligin 1 modulates striatal glutamatergic neurotransmission in a pathway and NMDAR subunit-specific manner. Frontiers in synaptic neuroscience, 7, 11-11.

Etherton, M., Foeldy, C., Sharma, M., Tabuchi, K., Liu, X., Shamloo, M., Malenka, R. C. & Suedhof, T. C. (2011). Autism-linked neuroligin-3 R451C mutation differentially alters hippocampal and cortical synaptic function. Proceedings of the National Academy of Sciences of the United States of America, 108(33), 13764-13769.

Gao, R. & Penzes, P. (2015). Common Mechanisms of Excitatory and Inhibitory Imbalance in Schizophrenia and Autism Spectrum Disorders. Current Molecular Medicine, 15(2), 146-167.

Nosyreva, E. D. & Huber, K. M. (2006). Metabotropic receptor-dependent long-term depression persists in the absence of protein synthesis in the mouse model of fragile X syndrome. Journal of Neurophysiology, 95(5), 3291-3295.

Rojas, D. C. (2014). The role of glutamate and its receptors in autism and the use of glutamate receptor antagonists in treatment. Journal of Neural Transmission, 121(8), 891-905.

Zalfa, F. & Bagni, C. (2004). Molecular insights into mental retardation: Multiple functions for the Fragile X mental retardation protein? Current Issues in Molecular Biology, 6, 73-88.

Image by Isuru Priyaranga

Some mentions about the latest topic

Posted on by Iasmina Hornoiu

Some of you have emailed me asking about what things we should stay away from during pregnancy, in order to avoid changing the normal course of a baby’s development. If you remember from the article about gender identity and sexual preferences see here, one of the most important factors in an individual’s development is represented  by sex hormones like androgens and oestrogen. They begin acting on our bodies in early pregnancy and even slight modifications in their functioning may dramatically affect our personality, preferences and behaviour as adults. 

Given external factors can greatly influence these hormones, it is very important to know which ones fall into the category of risk factors and therefore possibly affect our development. As expected, these factors pose a threat during pregnancy, which is why pregnant women should be particularly cautious about their life style. 

It has been suggested that taking aspirin while pregnant might increase the chance of the mother giving birth to a “more masculinised girl”. This is due to the actions of aspirin as a cyclooxygenase inhibitor; cyclooxygenase enzyme converts arachidonic acid into prostaglandins which apart from their well-known role in immune reactions, also seem to be involved in sexual behaviour. A decrease in the production of these compounds in female rats is thought to account for their man-like behaviour. 

Other factors that present a risk of having a lesbian daughter are smoking and synthetic drugs. The exact mechanisms of their actions is still unclear and it might turn out that they are not in fact such a threat. But it’s always better to prevent something rather than be oblivious to it. 

Also, stress during pregnancy can induce homosexuality in children, due to raised levels of cortisol which affects the production of sex hormones. So women caring a baby should try to stay as calm and relax as possible, even though that sounds like such a hard task especially when you’re pregnant! 

If you have any other questions or you would like to add your thoughts to this post, do not hesitate to leave a comment. 

Why drugs are actually bad!

Posted on by Iasmina Hornoiu

We are all well aware of how serious and, unfortunately, wide-spread drug addiction is, yet we don’t actually know what makes people so dependent of a drug after they have started using it. Even more intriguing is why former addicts, who have stopped using drugs for weeks or months, revert back to drug use, knowing full well that the substance they were addicted to in the past pretty much ruined their lives.

As I am sure you expect this article to shed light on the problem, I’m not going to keep you guessing. Two weeks ago, a team of researchers at the Icahn School of Medicine in US published a greatly revealing study in The Journal of Neuroscience. They appear to have found the answer to how cocaine affects decision-making in addicts as well as why abstinent users often choose to start taking cocaine again.

Dopamine is one of the commonest neurotransmitter in our brains. It is involved in many cognitive processes, including prediction and recognition of loss. Therefore, dopamine plays a very important role is some mental and also neurodegenerative diseases, such as schizophrenia (where dopamine levels are overly increased) and Parkinson’s disease (caused by decrease in dopamine secretion in the midbrain and degradation of dopamine receptors).

This recent study shows that cocaine acts on dopamine signalling, influencing the so-called Reward prediction error (RPE). It has been recorded, fallowing neuroimaging and pre-clinical studies, that dopamine signalling is increased in response to an unpredicted reward (which is scientifically referred to as positive RPE) and decreased as a result to a negative outcome or the omission of a predicted reward (negative RPE). The team of researchers demonstrated, therefore, that cocaine reduces the response to unpredicted loss (impaired negative RPE), while leaving the positive RPE almost intact.

In order to obtain these results, the team used 75 subjects, who were divided into two groups: 25 non-cocaine users and 50 cocaine addicts. Moreover, the second group was also divided as fallows: 25 cocaine users who had taken cocaine within 72 hours of the study and 25 cocaine users who had abstained from taking cocaine within 72 hours of the study. All subjects had to play a computer game that involved prediction and guessing.

As you may expect, the non-users responded normally to both unexpected  loss and predicted reward, as well as to predicted loss and unpredicted positive outcome. On the contrary, the cocaine users responded far less to unexpected negative outcome. This means that their brains were reacting less strongly to the negative result of a prediction than the normal subjects’ brains.

Moreover, and this is the most fascinating part, the users who hadn’t taken cocaine within 72 hours, showed deficit in positive RPE, whereas the other addict group (who had consumed cocaine in the previous 72 hours), had unaffected positive RPE, but impaired negative RPE. Also dysregulation in serotonin system in drug addicts might lead to this kind of results (serotonin signalling has been registered in response to negative prediction, in normal brains).

So, to cut the story short and in a more simplified version, if you use cocaine, you are more likely to omit the bad things in your life. But if you take cocaine and then you give up, you get the opposite result: you become less able to enjoy positive aspects. This might account for the fact that people who stopped taking drugs tend to start using them again after rehab. Does this mean we have to become drug addicts? It seems like this is the solution. Well…NO! Definitely not! And I’m not saying this because I might get into trouble for promoting drug use, but there is a very important reason for that. We DO need to anticipate and recognize negative outcomes. This is how all creatures in this world survive. This is how more advances creatures (like humans) are capable of making good decisions and learn from mistakes.

Some might argue, though, that it is preferable to be happy all the time, despite how much you fail and that there is no such thing as actual failure, as it’s all about how our own brains perceive the environment. What do you think? Is this true or not? Either way, I strongly suggest you don’t start using drugs!

The study

Image modified by Isuru Priyaranga