#SfN13 Tackling depression from both ends

503.Mood Disorders: Preclinical Studies and Animal Models.

503.08. Characterization of CX614, an AMPAkine, as a fast onset antidepressant
HM JOURDI, M KABBAJ; 
Biomed. Sci., Florida State Univ., Tallahassee, FL

503.09. Vortioxetine improves a reversal learning deficit in rats induced by serotonin depletion or chronic stress. DA MORILAK, A WALLACE, A PEHRSON, C SANCHEZ-MORILLO; Pharmacol. and Ctr. for Biomed. Neurosci., Univ. of Texas Hlth. Sci. Ctr., SAN ANTONIO, TX; Lundbeck Res. USA, Paramus, NJ

www.rochetfamilychiro.com

            Source: http://www.rochetfamilychiro.com

People generally consider depression as something purely emotional – an inescapable distaste towards oneself, an unshakable apathy towards the world, a persistent slow, sticky feeling of exhaustion, as if walking the path of life with glue on both feet.

Yet depression has a strong cognitive component, one so powerful that some scientists believe it to be the root of emotional imbalance. Many sufferers describe their thought patterns as “stuck in a rut”, where they’re only capable of framing things in a negative light, thus seeing the world as pale and hopeless. This observation has prompted two groups of researchers to ask: can we treat depression by targeting cognitive inflexibility?

AMP-A(p) the synapse

Luckily for researchers from Florida State University, we already have a class of cognitive enhancers on the market. AMPAkines are known to enhance attention span and improve learning and memory in the elderly and those suffering from neurodegenerative diseases. These drugs get their name from strongly enhancing the function of the AMPA receptor as a positive modulator. Interestingly, ketamine, the club-drug-turned-fast-acting-anti-depressant requires AMPAR activation to work, suggesting that AMPAkines may not only alleviate depressive symptoms but also act more rapidly than traditional anti-depressants.

Researchers gave a group of young adult rats a single injection of either ketamine or CX614, one of the best-characterized AMPAkines. 24hrs later, they exposed the rats to water and measured how long they swam before giving up in despair. Compared to saline-injected control animals, both ketamine and CX614 reduced the amount of time they spent immobile, though ketamine was slightly more effective at the doses used.

In another cohort of rats, researchers used a stressor (they didn’t say what, but it could be anything from bullies to cats to robots) to acutely trigger depression-like symptoms. Rats have quite the sweet tooth; normally given the choice between sugar and plain water, they lap up the sweet stuff in earnest. However, once depressed, they seem to loose the ability to enjoy life’s pleasures and no longer prefer the treat. Once again, a single injection of either ketamine or CX614 restored their love for sugar within a day. Remarkably, the antidepressant-like effects of CX614 lasted up to 8 days, even longer than that of ketamine.

On the molecular level, many previous studies show that depression reduces the number of synapses, thus negatively affecting the way neurons communicate. In fact, ketamine is known to rapidly reverse this defect, which may be one of the reasons behind its anti-depressant effect. Does CX614 work in the same way?

Using brain tissue isolated from CX614-injected animals, researchers found that within 30min neurons in the hippocampus were actively making more proteins, as evidenced by increased activity of the protein translation machinery. At the same time, CX614 also triggered a cascade of molecular signalling to reconstruct and stabilize actin, a “skeletal” protein that helps a cell maintain or alter its structure.

Dendritic_spines

Anatomy of a spine. Wikipedia

These two processes – protein translation and actin remodelling – allow neurons to form new spines, the little protrusions along dendrites that host synapses formed with (typically) another neuron. In other words, spines provide an anatomical structure for synaptic transmission. Although researchers did not directly prove their case with imaging techniques, these molecular changes certainly suggest that CX614 increases synapse formation.

Thus, like ketamine, AMPAKines may rapidly reduce depressive symptoms; unlike ketamine, they have very low potential for abuse. Whether their cognitive enhancing effects directly contribute to anti-depression though will have to be answered another day.

Flexible thoughts, sunny mind?

Researchers from the University of Texas and Lundbeck Research took the opposite approach – they picked an anti-depressant and investigated its cognitive enhancing effects. Vortioxetine is a selective serotonin reuptake inhibitor (SSRI) like Zoloft and Celexa. However, it also directly binds to and activates numerous types of serotonin receptors, giving it a unique pharmacological profile.

As mentioned above, patients with depression are often unable to flexibly reframe their thoughts. Neuroscientists can identify and measure a similar deficit in rats with a rather sneaky task. They first trained rats to dig for cheerios (yum!) from several pots, some of which smelled like cloves, others nutmeg; some filled with dry grainy sand, others with moist soft dirt. Unbeknownst to the rat, the digging material was just a distraction. Scent was the only clue they had to follow to find the treat.

After rats finally figured out the rules of the game, researchers suddenly switched the cheerios from the clove-sand pot to the nutmeg-sand pot, sat back, and watched how fast the rats updated their strategy as a measure of cognitive flexibility. In the first set of rats, researchers depleted ~90% of their serotonin levels with a chemical, thus coarsely mimicking the dearth of serotonin transmission seen in depressive patients. Unsurprisingly, they performed horribly, steadily going back to the original pot. However, when researchers gave them an injection of Vortioxetine 30min before testing, they rapidly ditched the old pot for the new.

Researchers then stressed a new group of rats with bouts of intense and unpredictable cold for 14 days straight. This treatment is often used to trigger deficits in reversal learning as well as depression-like behaviours (imagine being randomly thrown into a fridge for two weeks – you’d be constantly on edge and most likely depressed by the end too!). In the meantime, some rats received Vortioxetine in their food while others got placebo. In the end, those on placebo failed miserably on the cheerio-finding task, while those treated with Vortioxetine performed just as well as non-stressed controls.

These results suggest that Vortioxetine, an SSRI-type antidepressant, improves cognitive flexibility in stressed-out (and perhaps depressed) rats. However, the researchers did not show whether it also relived depressive-like symptoms at the doses used, how long the effect lasted, or whether the drug would perform in other (arguably more common) models of depression such as social defeat.

Taken together, these two studies complement each other beautifully, even though the results are still preliminary. Depression is a tough nut to crack, but the search for novel and fast-acting anti-depressants is in full swing. Among those presented at #SfN13 are the anesthetic gas isofluorane and the anti-cough medication dextromethorphan. Unfortunately as of now neither are ready for clinical use for depression.

The discovery of ketamine revolutionized the field of anti-depressant research in the last decade or so. Perhaps tackling depression on both cognitive and emotional ends – with cognitive enhancers or others – will prove to be even more effective at taming the beast.

Sappy little end-note: Back when I was studying pharmacy the best we could offer depressive patients were the atypical SSRIs, which takes weeks to months to start working. Many don’t respond to them at all and those who do built tolerance quickly. I’m so happy to have watched the story of ketamine unfold. If you’d like to know more, Gary Stix has a great 3-part series on Scientific American that’s well worth a read.

Check out my previous post on another potentially fast-acting anti-depressant L- acetyl-carnitine, a common fitness supplement.

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Feeling anxious? Run it out!

Woman running by the ocean beach at sunset

Run away from stress! Source: http://stronginsideout.com/

When life isn’t going well, I go for a run. I’ve always found running soothing. Maybe it’s due to “runner’s high”, the burst of endorphins that dampen physical pain and elevates mood. Maybe it’s because running increases the generation of new neurons in the brain (of mice), which we think is protective against depression.

Or maybe, as this new study shows, it’s because running tweaks the brain’s inhibitory circuits to directly dampen anxiety.

Schoenfeld et al. (2013) Physical Exercise Prevents Stress-Induced Activation of Granule Neurons and Enhances Local Inhibitory Mechanisms in the Dentate Gyrus” J. Neurosci. 33(18):7770-7777

Let’s first zoom in on the ventral hippocampus deep within the brain. This is one of the areas that process emotions, and is implicated in stress and anxiety regulation*. Increased activity in the ventral hippo is correlated (but not causative of) with anxious behaviour. Since running decreases anxiety, researchers wanted to know if runners’ ventral hippo respond differently to stress than sedentary people, in such a way that dampens anxiety.

(* You might remember the hippocampus is important for learning and memory – you’re right! However, increasing evidence is pointing to the dorsal hippo as the processing power behind memory. The hippo is quite a multitasker!)

elevatedPlusMaze

Elevated plus maze. I even find it scary! Source: http://www.cidd.unc.edu/

Since directly monitoring brain activity at the single neuron level from people is impossible, scientists turned to mice. If you ever had a pet hamster, you know that rodents love to run – give them a wheel and they’ll go at it for hours. After 6 weeks of voluntary running, scientists placed these mice onto an elevated maze with two dark closed arms and two light open arms (imaging a cross-like mountain with cliffs at the ends, pic left). Runners showed significantly less anxiety as they explored the open “cliffs” than their sedentary peers. They also had more newly born neurons in their brains.

So running decreases anxiety, but is it through lowering hippocampus activation? To tackle this question, scientists exposed the mice to cold water. If you’ve ever tried a New Years polar bear swim, you’ll know that swimming in cold water is very stressful. Indeed, in sedentary mice, cold-water stress caused a spike in neuronal activity in the ventral hippo, as measured by a set of genes that transiently and rapidly get turned on in response to neuron activation. These immediate-early genes act as messengers to tell the neuron to start making proteins to adapt to the stimulus, and are a reliable sign of recent neuron activity.

As you can see below, couch-potato mice showed a spike in neuronal activity (Sed, black bar with a star), as measured by immediate-early genes c-fos and arc. This response was almost completely wiped out in the runners (Run, black bar with no stars). So running decreases ventral hippo’s willingness to react to stress, leading to less anxious behaviors. But how?

Screen Shot 2013-07-10 at 2.50.58 PM

The activity of neuronal circuits is mainly balanced by two antagonistic neurotransmitters: glutamate-mediated excitation and GABA-mediated inhibition. Most anti-anxiety meds right now work by increasing GABA signaling. Researchers found that runners had significantly more GABA neuron activation when exposed to cold-water stress. These mice also released more GABA neurotransmitter, especially during the period of stress (see the peak in the black line below?). So maybe increased GABA in runners is enough to increase inhibition and dampen ventral hippo activity?

One way to test this is to block GABA signaling and see how these runner mice behave. To test for anxiety, researchers brought back the elevated plus maze. As you may remember, this maze has two dark, chill closed arms, and two brightly lit open arms. Usually mice prefer to spend more time in the closed “safe” arms, and this is indeed the case with sedentary mice (white bar). However, runners showed increased exploration of the open “cliff” arms of the elevated maze just like before (black bar). They were way less anxious about the light and openness of those cliff-like arms.

Screen Shot 2013-07-10 at 2.55.09 PMNow, if you block GABA signaling with a chemical called bicuculine in runners, these mice (grey bar above) behaved just like sedentary mice (white bar). Their anxiety returned! Bicuculine only worked when given to the ventral hippo; if you block GABA in the dorsal hippocampus – important in learning and memory but not mood – it didn’t affect the runners’ anxiety levels. These results tell us that increased GABA signaling lowers ventral hippo activation, and this leads to decreased anxiety.

Overall the researchers pretty convincingly show that running reduces anxiety through activating GABA signalizing in the ventral hippocampus. It would’ve been nice to see how runner vs sedentary mice behaved in the maze AFTER cold-water exposure, ie if running can “immunize” mice against stress-induced anxiety as well. It would also be interesting to see how long this anti-anxiety change lasts once the runners stopped running – does GABA signaling go back or does it stay responsive for a long time?

Regardless, this study gives you another reason to go out for a run and keep running. Try it for three weeks (how much the mice ran) and see if it helps with stress and anxiety. Science says it does.

ResearchBlogging.org
Schoenfeld TJ, Rada P, Pieruzzini PR, Hsueh B, & Gould E (2013). Physical exercise prevents stress-induced activation of granule neurons and enhances local inhibitory mechanisms in the dentate gyrus. The Journal of neuroscience : the official journal of the Society for Neuroscience, 33 (18), 7770-7 PMID: 23637169

I gut a feeling!

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Hey, we matter! Source: google “giant microbe plushies”

I bet you don’t think about the 100 trillion microbugs thriving in your gut too much. Neither did I, until I started reading up on the Human Microbiome Project (HMP) at a conference last week. Several fun facts that came out from the project:

    • For every human cell, there are 10-100 times of microbe living in your gut in harmony. Not to mention the skin, nose, mouth and foot dwellers. We’re really more bug than man.
    • People host very different types of microbug (over 1000!); but when you look at the GENES that compose each microbiome, they’re remarkably similar.
    • Along the same lines, an extremely diverse microbe composition can activate the same METABOLIC pathways to help you digest carbs and influence your metabolism – all (normal)microbug roads lead to metabolic Rome.
    • So it’s probably not surprising that aberrant microbug-ecology is involved in Type 2 Diabetes, Inflammatory Bowel Disease and MAYBE cardiovascular disease.
    • There’s tantalizing (but little) evidence that environmental bacteria may get into healthy brains and start colonizing.
    • One for the ladies: we can be “bug typed” into 5 categories, depending on our vaginal microbiome composition. Like blood type.

And finally, most interesting to me, is the emerging brain-bug connection. Microbes rapidly and densely settle in newborns as their brains are still developing. If the bad (pathogenic) ones get in, it may drastically increase a child’s chance of developing schizophrenia and autism. If the “normal” ones don’t get in – well, it seems to influence mood, anxiety and even cognition, at least in mice.

Let me explain.

Since we can’t ethically eliminate normal gut microbes in human newborns, scientists turned to germ-free (GF) mice, or mice without intestinal flora. When tested for anxiety levels, adult GF mice were much bolder than their controls, wandering into terrifying bright fields and cliff-like arms of an elevated maze. This brash behaviour disappeared if they were artificially colonized with gut flora when young, but not once they reached adulthood.

This tells us that –all else the same – gut bugs can impact behavior, depending on whether or not they were present in the “critical period” in development.

Screen Shot 2013-06-07 at 4.27.12 PM

“Conv” = gut microbe (poop) transplant. If gut flora settle down & flourish before or during the critical period, germ-free (GF) mice show normal anxiety behaviour. Otherwise they turn into brash adults. Source: below #2

But it’s not just the kids that are susceptible. Giving adult mice a mixture of ANTIbiotics and antifungals for a week reduced their anxiety-like behaviors, which went back to baseline 2 weeks after the treatment stopped. This doesn’t imply gut flora’s bad for mood – a dose of PRObiotics (L. rhamnosus) also made healthy male mice gutsier. So the absolute amount of gut flora may not matter as much as composition in this case.

So HOW are normal bugs in the gut signaling to the brain? Scientists aren’t too sure yet, but peripheral and gut nerves may be involved. Gut bugs may also be generating neurotransmitters from food, which gets delivered to the brain by blood. They could also be communicating with the brain indirectly, by changing global metabolism. Alternatively, a crazier idea is that gut bugs can change protein expression in the brain – at least during early development – and so the brain “sets up” its synapses and circuits differently, eventually changing how stress and mood is processed.

There is some evidence for this. We know that monoamines, like dopamine and serotonin, are involved in mood regulation. Surveying the brains of bug-free GF mice, scientists found increased metabolism of monoamines in the striatum, a brain area important for motivation, motion initiation and reward learning. Zooming further in, at the synapse, the levels of two proteins involved in neurotransmitter shuttling and synapse maturation were changed. So were a cluster of genes related to learning (plasticity) and depression. Remember, the only thing that differed GF and control mice is their lack of gut bugs. When scientists gave young GF mice normal gut flora from a donor (read: poop implant), several synaptic protein levels returned back to normal, as did behaviour.

Screen Shot 2013-06-08 at 2.52.32 PM

Proteins involved in anxiety and learning are expressed differently in control (SPF-left) and bug-less (GF-right) mice. For those interested, A is NGF-1A, B is BDNF

So mice microbiome tweaks mice behavior. But what about humans? In one double blind, placebo-controlled 30-day trial, healthy volunteers given probiotics (L. helveticus & B. Longum) reported less psychological distress than controls. In another similarly controlled trial, healthy volunteers were given probiotics or placebo for 3 weeks. Those who scored lowest on depressive moods showed significant improvement after probiotic supplementation compared to control. Finally, in a small pilot study with chronic fatigue syndrome patients, those who took probiotics (L. casei) daily for 2 months showed significantly fewer anxiety symptoms than did the placebo group.

mguts

The “second brain” bugs the brain. Source: http://www.columbia.edu

You may think that everything described above sounds a little iffy (Why look at those proteins and genes and brain area? Why use that strain of probiotic? Why do antibiotics and probiotics show similar anti-anxiety effects?). I tend to agree. The gut-brain-behavior field is still in its infancy – what we do know if that the human microbiome is important, in health and disease. Whether they’re good targets for anxiety and depression treatment though, is still an open question. So maybe it’s not yet time to drop the Prozac and pick up the probiotics.

I’ll leave you with this: since what we eat heavily affects the composition of gut flora, and gut flora affects our brains, there is some scientific truth in the old saying “you are what you eat”.

Thoughts?

ResearchBlogging.org
Diaz Heijtz R, Wang S, Anuar F, Qian Y, Björkholm B, Samuelsson A, Hibberd ML, Forssberg H, & Pettersson S (2011). Normal gut microbiota modulates brain development and behavior. Proceedings of the National Academy of Sciences of the United States of America, 108 (7), 3047-52 PMID: 21282636

ResearchBlogging.org

Foster JA, & McVey Neufeld KA (2013). Gut-brain axis: how the microbiome influences anxiety and depression. Trends in neurosciences, 36 (5), 305-12 PMID: 23384445

Antidepressant epigenetic action of a common fitness supplement

A short note on the history of antidepressant research: From MAOIs/SSRIs to ketamine and BDNF

Traditional antidepressants, like Prozac, don’t work too well. Back in the 50s, researchers thought that depression was caused by a depletion of a group of neurotransmitters in the brain known chemically as the monoamines (i.e. serotonin, noradrenaline, dopamine).  Hence, the reasoning goes, upping monoamine levels should treat depression. Unfortunately, even first-line drugs (such as Prozac) are effective for only ~40% of Major Depression cases. They also have a delayed onset time of weeks to months, and are accompanied by a slew of nasty side effects. In 2006, the field of antidepressant research was shocked by the discovery that ketamine – a dissociative club drug – has fast-acting antidepressant & anti-suicidal affects lasting longer than the duration of the drug. Ketamine works on the glutamate system, which is the main excitatory neurotransmitter in the brain, and results in a rapid increase of a protein called Brain-Derived Neurotropic Factor (BDNF). BDNF increases the formation of new synapses and reverses neuronal abnormalities in the prefrontal cortex. On the circuit levels, this leads to functional “rewiring” or “resetting” of connection between neurons, which may underlie rapid behavioral changes seen with ketamine administration. This discovery led to the “synaptogenic” hypothesis, which stipulates depression is not due to lack of monoamine neurotransmitters per se, but the inability to maintain normal synapse formation. It seems like the antidepression field is going through a paradigm shift, placing BDNF and the glutamatergic system front and central as targets for new generation antidepressant targets. Exciting times!

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Depression literally wilts your brain. In patients suffering from major depressive disorder (MDD) and rats undergoing chronic stress, their neurons are fewer, smaller, and host shrunken dendrites with malfunctioning synaptic connections. MDD patients also generate fewer new neurons, effectively cutting off the supply chain. All these morphological and functional changes lead to disrupted neuronal communication in the cognitive-emotional circuitry, leading to depressive symptoms. Tranditional antidepressants, like Prozac, can block or reverse these deficits – but only in ~40% MDD patients. They also require weeks to months to work, and often come with intolerable side effects. Not good!

In search for fast-acting antidepressants, researchers stumbled upon ketamine, the notorious dissociative club drug, which amazingly reverses depressive symptoms only hours after administration. Ketamine’s magic lies in its ability to act on the excitatory glutamate neurotransmitter system, causing an increase in the “nurturing” protein Brain-Derived Neurotropic Factor (BDNF), which leads to formation of new synapses. Unfortunately, although valuable, ketamine’s psychoactive effects and addictive potential lowers its potential as an antidepressant pill.

So the search continues…

Is this the answer?

Is this the answer? Soooo many brands available OTC.

…And somehow, researchers find a fitness supplement.

Nasca et al. 2013. L-acetylcarnitine causes rapid antidepressant effects through the epigenetic induction of mGlu2 receptors.PNAS 110 (12):4804–4809.     

L-acetyl carnitine (LAC) is an amino acid derivative involved in energy metabolism and fatty acid oxidization, and is frequently sold as an energy-enhancing fat-loss supplement in fitness stores. Clinically, it is used to treat pain by acting on the epigenome – changing the expression of certain genes. Namely, LAC increases the expression of a glutamate receptor, mGlu2. Since mGlu2 is lowered in a genetically depressed line of rats (named FSL), the authors hypothesized that LAC may have anti-depressive effects through an epigenetic mechanism.

To test this, the authors got ahold of two strains of rats: the spontaneously depressive FSL, and the depression-resilient FRL. They also pitted LAC against a traditional SSRI antidepressant, chlorimipramine (CLO).  Now, how do you tell is a rat is depressed? Here, the authors used two main tests, the forced swim test, and the sucrose preference test. The former measures how much a rat is willing to fight for its life (depressed rats give up faster) while the later measures whether a rat takes pleasure in sweet tasting food (depressed rats show lower desire for sugar). FSL rats treated daily with LAC showed improved symptoms after only 3 days of treatment, while CLO took 14 days to see such an effect. LAC-treated rats also showed increased levels of BDNF, which as mentioned before, is crucial for the generation of new synaptic connections.

Forced swim test: depressed rats are less willing to swim.

Forced swim test: depressed rats are less willing to swim.

When researchers stopped giving the drugs (look at “days of withdrawal”), depressive symptoms rapidly came back in the CLO-treated group, but the effect of LAC persisted for at least 2 weeks after the treatment stopped. Unsurprisingly, none of the drugs affected the depression-resilient FRL rats. The authors further verified LAC’s antidepressant effects with a mice model of chronic stress exposure, which is thought to be a primary environmental cause of depression in humans.

Now we have a “black box”: in goes LAC, out comes happier rat. What’s happening inside the box? Well, the effect of LAC was abolished when coadministered with a mGlu2/3 blocker, suggesting that LAC is acting through mGlu2/3 to exert its effect. As mentioned before, mGlu2 levels in the hippocampus and prefrontal cortex are lower in the depression-prone FSL rats; LAC treatment increased both mGlu2 mRNA and protein levels to that of the FRL controls. Further analysis with pharmacological inhibitors showed that a transcription factor called NF-kappaB is involved in the upregulation of mGlu2 induced by LAC. A transcription factor acts as a “messenger”, mediating interactions between the environment and gene expression by directly binding to promotors on certain genes. Finally, LAC also changed the conformation of the histone proteins that the mGluR & BDNF gene is wrapped around, leading to a more “open” conformation that allows easier access to transcription factors to enhance gene expression. Essentially, all of the above shows that LAC can increase expression of mGlu2 and BDNF through an epigenetic mechanism, and (maybe) lead to formation of new synapses down the road.

Acetylcarnitine (the “AC” part of “LAC”) is produced naturally in the body, and can be acquired through diet by eating meat and diary (vegetarians are often deficient). Interestingly, the authors found that endogenous LAC levels were reduced by 40-60%in the prefrontal cortex and hippocampus of FSL rat, which may be one of the reasons they respond to LAC treatment. The authors didn’t further pursue this point – does low endogenous LAC predispose a person to depression? Is supplementing LAC “rectifying” this deficiency? LAC is heavily involved in fat metabolism – can a metabolic shift also promote an antidepressant effect?

Overall, this study identifies LAC as a potential fast-acting antidepressant with notably fewer side effects than existing options. While I’m not very convinced its action is mainly through epigenetic regulation of BDNF, it does support the idea of targeting epigenetic mechanism to develop new generation antidepressants (on the other hand, epigenetics is so hot these days EVERYONE wants a bite of it). For me, this study nicely illustrates the intricate interaction between foodstuff and cellular signaling beyond metabolism (see “The complicated science of a simple pleasure”).

I wonder if LAC will now be promoted as “fat metabolizer, nootropic and antidepressant all in one”.

ResearchBlogging.org
Nasca C, Xenos D, Barone Y, Caruso A, Scaccianoce S, Matrisciano F, Battaglia G, Mathé AA, Pittaluga A, Lionetto L, Simmaco M, & Nicoletti F (2013). L-acetylcarnitine causes rapid antidepressant effects through the epigenetic induction of mGlu2 receptors. Proceedings of the National Academy of Sciences of the United States of America, 110 (12), 4804-9 PMID: 23382250