#SfN13 Running boosts cognition by increasing aerobic capacity

Poster: 671.Learning and Memory: Genes, Signalling and Neurogenesis II.

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Running for health. Source: http://www.stthomas.edu/

There’s no doubt that aerobic exercise benefits the brain. Running, for example, reduces anxiety, improves sleep quality, boosts learning of a new task and maintains spatial memory*. Many of these mental perks stem from an increase in adult neurogenesis; that is, the birth of new neurons in the hippocampus and the olfactory bulb. (*That is, if rats run before new learning. See here for more.)

Yet perhaps the most apparent health benefit of running is increased cardiovascular and lung function. As any runner can attest to, an initially exhausting 10k soon becomes a breeze – you’ve increased your aerobic capacity. This led researchers from Duke University to wonder: is improving exercise capacity –by whatever means – necessary and sufficient to boost neurocognitive function?

Better bodies, better minds

Just like us humans, rats have an innate sensitivity to the effects of exercise. After the same 8-week running regime, high-response rats drastically increased their maximal capable running distance (~75%), while low-response rats barely improved (~22%). Surprisingly, compared to their sedentary peers, only high-response rats showed elevated neurogenesis in the dendate gyrus, a subregion of the hippocampus, as compared to their sedentary peers.

One hypothesized function of the dentate gyrus is pattern separation, or VERY simply put the discrimination between two very similar spatial contexts or things (Jason Snyder of Functional Neurogenesis fame has a great blog post on the matter). Researchers decided to challenge these rats with two Lego pyramids that only differed in the colour of their tops – imagine two Christmas trees with either a yellow or orange star. After the rats familiarized themselves with the yellow-topped Lego, researchers waited a minute before presenting them with both. High-response runners (but not their sedentary controls) instantly realized something was up – they approached and sniffed the new construct in earnest, ignoring the old familiar one.

Low-response runners, on the other hand, behaved just like their sitting peers, spending a similar amount of time with both objects. Low-responders had no problem with their memory; when faced with a mug and a can, they could easily discriminate between the two. They just couldn’t pick out minute differences in the Lego pieces, a skill often attributed to enhanced neurogenesis.

These data, perhaps somewhat dishearteningly, suggest that running doesn’t always boost brainpower – neurocognitive benefits only occur in tandem with improvements in aerobic fitness, as measured by total running distance until exhaustion. These results parallel that of a human study, in which increased lung capacity after training correlated with better performance on a modified pattern separation task (although understandably they did not show enhanced adult neurogenesis, so it’s hard to attribute behavioural output to increased new neurons per se).

Running-improved aerobic capacity seems to be the crux to exercise-induced brain benefits. But is running really needed? To explore this idea further, researchers decided to take treadmills out of the equation and focus on genetic differences in aerobic fitness.

Innate aerobic capacity accounts for cognitive benefits

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Rats on treadmills. Source: http://healthyurbankitchen.com/

Allow me to introduce to you the low and high capacity runners. Selectively bred for their capability (or not) to “go the distance”, these rats differ up to 3 times in a long-distance standard fitness test, without ever setting foot on a treadmill. At 10 months old, they also had a two-fold difference in the total number of newborn neurons in the dentate gyrus as a result of increased neuron survival, which increased to three-fold at 18 months old.

Researchers took sedentary rats from both groups and challenged them to the Lego task described above. High capacity runners significantly outperformed their low capacity peers, expertly telling apart the Lego constructs. Similarly, in an object placement task in which researchers minutely moved one of two objects, low capacity runners could not identify the moved one after an hour’s delay, though they managed if the wait was only a minute. High capacity runners, on the other hand, excelled in both cases.

These results argue that high aerobic capacity in and of itself promotes pattern separation. But what if, unbeknownst to researchers, high capacity runners were maniacally jumping around everyday in their home cages? A few days of stealthy observation proved this wrong; paradoxically, low – compared to high- capacity runners were much more hyperactive. They also seemed more outgoing in a social interaction test, and exhibited a lower tendency to generalize trained fear from one context to another.

Running-induced neurogenesis is generally considered to ease anxiety. So why do high capacity runners (with higher rates of neurogenesis) seem more neurotic?

Born to laze, born to run

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Sitting on a couch is really not that stressful. Don’t make me run!

Running is physiologically stressful in that it increases the level of corticosterone (CORT), a stress-response hormone. Unlike chronic stress that continuously elevates CORT, running only induces a transient, benign increase that quickly returns to baseline after recovery.

Researchers trained low- and high- capacity rats on treadmill running 5 days a week for a month. By the end, both groups showed increased running capacity, though trained low-capacity rats were only as good as untrained high-capacity ones (life’s unfair!). However, their acute stress responses drastically differed in a running-stress test.

Untrained low-capacity rats remained calm throughout the test, as measured by unchanging CORT levels. “They waddled on the treadmill for a bit, got tired and gave up.” said the researcher, “so they really weren’t that stressed out.” Trained low-capacity rats however hated the treadmill – their CORT shot through the roof. “You’re chronically forcing them to do something they’re terrible at, of course they’re going to be stressed out” explained the researcher, “and once they’re done, their CORT goes back to normal.” (I’m paraphrasing.) While this scenario is certainly possible, an alternative explanation is that only trained low-capacity rats were able to exercise to the point to induce a normal elevation in CORT levels; untrained rats simply don’t workout hard enough.

Intriguingly, untrained high-capacity rats had elevated levels of CORT during the running test, while previous training eliminated this response. Why? Researchers believe that chronic running habituated them to the stressor: “You know when you have this itch to run? You get stressed out when you can’t, and feel relieved when you finally do exercise.” In other words, these rats were “born to run”.

On the cellular level, running did not significantly increase neurogenesis in the ventral hippocampus in either low- or high-capacity rats, which I find rather surprising. Finally, high-capacity rats (compared to low) had less Mmneralocorticoid receptor (MR) and glucocorticoid receptor (GR) in the amygdala and hypothalamus, but not in the hippocampus. This is also surprising, as MRs and GRs in the hippocampus are crucial for negative feedback to the stress response axis (below).

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Hippocampal GR negatively regulates the stress response. Source: http://learn.genetics.utah.edu/content/epigenetics/rats/

Taken together, these data point to increased aerobic fitness– through genetic means or exercise- as the key to enhancing neurocognitive function in rats. Inbred differences in aerobic fitness may alter how one responds to exercise (and perhaps other types of) stress.

These studies beg the question: what if we could artificially mimic the effects of exercise (pharmaceutically or otherwise) and reap its benefits? While “exercise pills” may not necessarily benefit healthy individuals, they could potentially improve both physical and hippocampal health of the elderly or the disabled.

Such research is under way, though as of now the results are not yet convincing.

PS. This is the end of #SfN13 blogging. It’s been hectic, a bit overwhelming and a LOT of fun!! Thank you to all the presenters for your patience & feedback and the PIs who let me write about your work. Thank YOU for reading!

Regular research blogging will resume soon. Stay tuned!

671.01. CL Williams et al. Rats selectively bred for high running capacity have elevated hippocampal neurogenesis that is accompanied by enhanced pattern separation ability. 

671.02. KM Andrejko et al. Rats selectively bred for high running capacity have elevated hippocampal neurogenesis that is accompanied by a greater expression of hippocampal glucocorticoid receptors and altered contextual fear conditioning. 

671.04. JM Saikia et al. Treadmill exercise training only enhances neurocognitive function if it is accompanied by significantly increases in aerobic capacity. Duke Univ., Durham, NC; Univ. of Michigan Med. Ctr., Ann Arbor, MI

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#SfN13 Getting rid of an unwanted memory for good

Poster 99.06/JJJ40 – Gradual extinction prevents the return of fear. SJ Gershman, CE Jones, KA Norman, MH Monfils, Y NIV. Brain and Cognitive Sci., MIT, Cambridge, MA; Psychology, The Univ. of Texas at Austin, Austin, TX;Neurosci. Inst. & Dept. of Psychology, Princeton Univ., Princeton, NJ

Poster 99.07/JJJ41 Gradual extinction prevents the return of fear in humans. JW Kanen, SJ Gershman, MH Monfils, EA Phelps, Y NIV. Dept. of Psychology, Ctr. for Neural Sci., New York Univ., New York, NY;Dept. of Brain and Cognitive Sci., MIT, Cambridge, MA; Univ. of Texas, Austin, TX; Nathan S. Kline Inst. for Psychiatric Res., Orangeburg, NY;Princeton Neurosci. Inst. and Psychology Dept., Princeton Univ., Princeton, NJ

Psychiatrists have a problem. Memories, especially fearful memories, are exceedingly hard to erase. Say you’ve learned that every time you touch a doorknob in the winter you get a painful electrostatic shock; fairly soon you might form an irrational fear of the doorknob. What can the good doctor do?

doorknob

Ouch! Source: ashafullife.blogspot.com

The go-to therapy is extinction training. Here, you’ll repeatedly touch a doorknob that’s been treated to eliminate static – hence, no shock. After several sessions you loose your phobia. Great. Yet a few weeks later, you once again feel butterflies fluttering in your stomach at the thought of touching a doorknob. Somehow, the fear has returned.

The above scenario may seem ridiculous; yet for those suffering from post-traumatic stress disorder or debilitating phobias, the spontaneous recovery of a fear memory is nothing to laugh at. Scientists aren’t quite sure why this happens. Erasing a memory, or memory extinction, in theory “updates” the original memory trace, such that a fearful stimulus (eg doorknob) is now encoded as safe. Yet in practice, when the object of fear suddenly dissociates from harm (eg no more shocks!), the mPFC generates a large prediction error signal, such that the new information is treated as something entirely new and encoded in a separate memory trace.

Herein lies the problem. The original fear memory, alive and well, competes with the opposing new one for expression. Behaviourally, this often results in the return of fear. But here’s the silver lining: if you keep the prediction error signal small, the brain may opt to modify the old trace rather than encode an entirely new one, thus mitigating or erasing fear in actuality.

Researchers decided to test this theory out. First, they taught a cohort of rats to fear a tone by associating it with a shock. The rats were subsequently divided into three groups: the first received gradual extinction, in which the frequency of shock delivery declined gradually. In other words, as the trials progressed, rats more often than not experienced the tone without the shock. In a sense, researchers “weaned” these rats off the tone-shock association, thus triggering a small prediction error. The second group received the opposite treatment, with the frequency of shock delivery steadily increasing until the last 9 trials, in which all shocks were omitted to facilitate extinction. This is necessary as researchers wanted to observe the return of fear. The third group went through normal extinction; that it, only tones, no shocks. By the end, all rats lost their fear of the tone.

Fast-forward a month. Researchers returned the rats to the testing chamber and played the same tone. Rats that underwent gradual extinction showed significantly less fearful behaviour than the other two groups. In another experiment, researchers re-established the fear memory by giving the rats another shock. Once again, those that had undergone gradual extinction showed less fear. These results strongly suggest that gradual extinction is especially effective at persistently decreasing fear. But how do these results transfer to humans?

Using a similar fear-conditioning paradigm, researchers presented images of snakes to a group of volunteers. This was followed by an uncomfortable electrical shock to the wrist. Fear, as well as other states of arousal, increases sweating and skin conductance, the latter of which was carefully monitored to objectively measure the volunteers’ level of fear. Within a day, volunteers learned to fear the innocuous snake image.

One day later, researchers divided volunteers into groups and eliminated their fear memory through one of the three extinction processes as above. When tested on the third day, those who went through gradual extinction showed a trend towards less spontaneous recovery; that is, they sweated less at the sight of the snake images. However, the results are preliminary and due to the small number size (10-14 per group), the effect was not yet statistically significant.

Clarifying the conditions that facilitate persistent fear extinction may help clinical psychiatrists optimize extinction-based exposure therapies for the treatment of anxiety disorders and phobias. The evidence presented here – from rat to human – strongly suggest that minimizing prediction error through gradual extinction is a more effective way to modify and erase a memory, maybe for good.

Sometimes slow is a better way to go.

Shining light on the dark side of oxytocin

Almost everyone’s heard of oxytocin these days. Dubbed “the love/trust hormone” by pop neurosci, oxytocin is to “love” as dopamine is to “reward” – some truth, but WAY too oversimplified! Where to start? In the sack, oxytocin is involved in ejaculation latency, the big O and pair bonding. Out on the streets (or in labs), it helps people recognize facial expressions and recall others’ faces. It may enhance trust among strangers. It may be the key to monogamy, at least in prairie voles. It reduces anxiety and stress, and promotes social interactions. It may even tweak something as abstract as morality.

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Oxytocin’s functions are as complicated as its structure. Source: wiki

“So what if it’s not the love drug?” you might ask. Oxytocin still sounds like the most “amazing molecule in the world.” The problem is, individual people respond to oxytocin very differently. In one study, when socially anxious people were given oxytocin through inhalers, they remembered their moms as less caring and more distant. In another study in people with borderline personality disorder, oxytocin hindered trust and cooperation. Oxytocin also seems to ENHANCE – not mitigate as previously thought – fear and anxiety levels in people who’ve suffered through traumatic events. In these individuals, it even promoted stronger recall of bad memories.

Calling oxytocin the “love drug” is not only inaccurate, but also dangerous. Not recognizing this dark side of oxytocin exploits the vulnerable – those suffering from post-traumatic stress disorder, autism, depression or social anxiety disorder, who think that an internet-bought nasal spray will help them ease their illness. Understanding how oxytocin regulates fear and anxiety is especially important, as the hormone is currently being researched as a potential anti-anxiety drug.

We know a lot about what oxytocin does. We just don’t know how it’s doing it. Oxytocin is released by the hypothalamus, situated at the base of the brain. As a hormone, it circulates and acts throughout the body and the brain. Could it be that oxytocin is acting at different sites in the brain to produce diverse actions? Under what conditions will it promote fear and anxiety? How is it enhancing fear recall?

YF Guzmán et al. (2013) Fear-enhancing effects of septal oxytocin receptors. Nature Neuroscience, doi:10.1038/nn.3465

The authors of this paper tackled these questions head on with two strains of genetically modified* mice: one lacking, and one having more of the oxytocin receptor in an area of the brain called the lateral septal (LS). Just like small molecule neurotransmitters (think dopamine, serotonin etc), oxytocin needs to bind to its receptor to have an effect; manipulating receptor levels in essence eliminates or boosts oxytocin signalling. The researchers chose the LS to study as it contains large amounts of the oxytocin receptor (so under normal circumstances oxytocin is probably doing something there), and because it’s heavily involved in stress and fear. (* For those wanting the nitty-gritty, overexpression and knockdown was achieved through local viral injection of the appropriate vectors, not whole-animal knockdown)

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Contextual fear conditioning. Ouch!

Researchers first tested if oxytocin is directly involved in fear in non-stressed mice. They took the two mutants and normal mice and put them in a distinctive box. They then zapped the mice with a small shock. Mice like electrical shocks as much as you – they’ll quickly associate the box with the shock, and freeze in fear when they’re put back into the box a day later. The idea is, if oxytocin signalling in the LS is involved in enhancing fear, then having more oxytocin receptors should increase freezing.

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Which didn’t happen! As you can see, neither increasing (dark blue bar) nor decreasing (light blue bar) oxytocin receptors had an effect on freezing, compared to the controls (white bar). This suggests that in normal, unstressed individuals, oxytocin in the LS does NOT directly regulate fear and anxiety. Could it be that oxytocin plays a more modulatory role in fear then? As in, it will only promote fear when an individual is already stressed?

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Reminds my of my elementary school years. Sigh.

To test this hypothesis, researchers first needed to stress out the mice. While you can do it with robots, researchers settled on a more socially relevant method: social defeat. They put a large, aggressive bully into the mice’s habitat, and let the him intimidate the mice for 6 hours. Previous results tell us that social defeat increases oxytocin release in the LS, and if extended for long periods, can induce symptoms like depression and social withdrawal in the bullied. After a tortuous 6 hours, researchers removed the mice and once again, shocked them in a box and tested them for freezing a day later.

Screen Shot 2013-07-24 at 12.59.09 PMAs you can see in the left graph, social defeat dramatically increased freezing in normal mice (first two bars, WT/wild-type, orange compared to grey), but this was completely abolished by wiping out oxytocin receptors (last two bars, green bar compared to grey). On the other hand (right graph), in mice subjected to social defeat, mice that have more oxytocin receptors (dark blue bar) froze much more than normal mice (orange bar). These results tell us that oxytocin enhances fear in stressed individuals, but doesn’t affect normal mice.

So what’s going on? Is oxytocin enhancing the EXPERIENCE of social defeat, in which the mice perceive a small aggressor as a more intimidating one? Researchers noticed that all bullied mice, regardless of oxytocin receptor levels, behaved similarly – those having more oxytocin receptors did not cower more than normal. Perhaps oxytocin is not changing the social interaction per se, but enhancing the bad memory of being tormented?

To test this, researchers put the defeated mice back together with the bully. While normal mice tentatively approached the bully several times, mice with more oxytocin receptors kept their distance. Mice without oxytocin receptors seemed to have forgotten the episode and hanged around the bully way more than normal mice. So it does seem that increased oxytocin signalling enhances bad memories, and predisposes a traumatized individual to more fear and anxiety when subjected to further stress later on.

Researchers then tried to figure out how oxytocin strengthens a bad memory, and identified a protein called ERK1/2 as a main signalling messenger. When they inhibited ERK1/2 with a drug called U0126 (black bar on the far right), the effects of social defeat on enhancing bad memories (orange bar) were eliminated. The drug did not affect fear memory in non-stressed (NS) mice (grey and black bars on the left). Interestingly, oxytocin activates alternatively signalling proteins in other brain regions such as the central amygdala, which DECREASES anxiety. So it seems that oxytocin is “two-faced”, and depending on which brain area it’s activating on, can enhance both “love” and fear.

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In mice stressed out from social defeat (SD), inhibiting the messenger ERK1/2 with U0126 erased oxytocin’s enhancing effect on bad memories. NS: no social defeat.

As mentioned before, oxytocin circulates throughout the body and the brain. It would be interesting to see how systemic oxytocin influences fear memory. Could it be that stress differentially alters oxytocin receptor levels in different areas of the brain, changing the balance between promoting and eliminating fear? Does oxytocin have the same effect on different types of stress? Does oxytocin signalling in the LS go awry in people with anxiety disorders? Perhaps giving nasal oxytocin is not the best anti-anxiety med, and targeting its downstream signalling pathways in fear-inducing brain areas (like the LS) might be a better approach?

Finally, what is the role of oxytocin in influencing individual behaviour in social interaction? This study clearly tells us that oxytocin does not unidirectionally decrease anxiety. Maybe, as the authors suggested, it is a signal that focuses our attention to different social contexts and cues, making them more noteworthy and our experiences more long lasting. We don’t yet know. Hopefully, more research will continue to reveal the multiple faces of this complicated and fascinating molecule.

ResearchBlogging.org
Guzmán YF, Tronson NC, Jovasevic V, Sato K, Guedea AL, Mizukami H, Nishimori K, & Radulovic J (2013). Fear-enhancing effects of septal oxytocin receptors. Nature neuroscience PMID: 23872596

Note: For those interested in learning more about oxytocin, @Scicurious has an awesome blog series going on. Check it out!

Edit: Thanks to Samuel for pointing out in the comments that oxytocin is also considered a neurotransmitter.

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?

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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.

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“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.

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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.

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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

#CAN13 Can a brain scan predict your vulnerability to anxiety disorders?

Poster: Increased Activity of Frontal and Limbic Regions to Emotional Stimuli in Children At-Risk for Anxiety Disorders. R Christensen, University of Toronto.

fmri

TL;DR: no.However, a new study reports that functional changes do occur in the brain long before anxiety disorders first strike.

Genetic studies tell us having one parent with anxiety disorder significantly increases a child’s chance of getting the same disorder. Because of this genetic basis, researchers believe that early changes in a high-risk child’s brain may precede full-blown disorder.

To test this hypothesis, they recruited 25 high-risk and 20 low-risk kids. To meet “high-risk” criteria, the kids must have at least one parent diagnosed with anxiety disorder. Low-risk kids are those with parents with no psychiatric illness. Researchers then put the kids into an fMRI machine, and showed them a computer-generated face with different expressions. Some were neutral (think passport photos), while others were either happy or angry.

Both groups of children responded to neutral faces similarly. However, when high-risk kids looked at emotionally rich faces (both angry and happy), their brain activity skyrocketed to way beyond that of low-risk kids. The limbic and frontal regions were especially hyperactive. We know that the limbic system is involved in emotion processing, while the frontal system modulates anxiety.

Surprisingly, at the time of study, only 4 kids were diagnosed with some sort of anxiety disorder. However, 76% eventually developed anxiety-related disorders, such as social phobia, panic attacks and agrophobia.

These results show that fMRI has some predictive power, but that doesn’t mean that it’s ready to hit the psychiatry stage as a diagnostic tool. The correlation between enhanced frontal/limbic processing and anxiety disorder risk only appeared on AVERAGE. That is, we see the link only when looking at the population level. Ours brains are unique little flowers: each person, regardless of risk for anxiety, will show a different pattern of activation. At the moment, the gold standard is still the psychiatry bible, DSM-V.

However, this doesn’t mean we shouldn’t try to get there. As the director of the National Institute of Mental Health said “It is increasingly evident that mental illness will be best understood as disorders of brain structure and function that implicate specific domains of cognition, emotion, and behavior.”

Note: This is the last post on CAN. Overall it’s been very fun! I HIGHLY recommend checking out the work of Helen Meyburg on Deep Brain Stimulation as a treatment for depression (Youtube), and Shayna Rosembaum‘s work on amnesia. 

Drinking doesn’t sooth the soul

Bolder, Colorado

You’re in the theater, completely engrossed. You wipe away a tear at Albert’s departure, at Bruce Wayne’s broken body, at the demise of Gotham. Then you smell the smoke. See the panic. Hear the scream.

People deal with traumatic experiences differently. Some are able to work through painful memories, eventually returning to their daily lives. Others drown in feelings of pervasive fear and hopelessness, persistently re-experiencing the trauma in dreams or in flashbacks, impairing any attempt at a normal life. People with anxiety disorders may drown in alcohol, wishing to drink their fears away.

Unfortunately, alcohol may be one of the things impairing critical brain mechanisms for recover from trauma.

Holmes et al., 2012. Chronic alcohol remodels prefrontal neurons and disrupts NMDAR-mediated fear extinction encoding. Nat Neurosci. 2012 Oct;15(10):1359-61. doi: 10.1038/nn.3204. Epub 2012 Sep 2.

From a neurobiological point of view, conditioned fear is a memory, linking an event or object to the biological fear response. As such, it can be encoded, strengthened, retrieved, and extinguished.  Extinction of a memory is not really “forgetting” it – it doesn’t erase the fear memory trace in the brain. Instead, the brain learns a new association, that whatever you were afraid of (worms!!!) is actually harmless – this new memory trace, thought to be encoded by the medial prefrontal cortex (mPFC), competes with the conditioned fear memory when you’re re-exposed to the source of terror. If it wins, the fear memory is not expressed – that is, you wouldn’t experience the terror associated with the trigger.

Chronic alcohol use is known to affect the mPFC, changing its size, neuron number and activation, leading to deficits in attention and higher cognitive function. Given mPFC’s critical role in fear memory extinction, would heavy drinkers be more vulnerable to anxiety disorders following a traumatic event?

Researchers doused mice with vaporized alcohol with a schedule mimicking cycles of “heavy drinking” as seen in alcoholism, with a total amount roughly equivalent to twice the legal driving limit in humans. The mice were allowed to rest for two days to nurse their hangovers, and then were trained to fear a tone by pairing the tone with an electric foot shock.  As it turns out, these alcoholic mice learned to fear the tone as fast as normal mice, showing no problem with memory encoding.

To extinguish the memory, the researchers played the tone again and again without the foot shock. Compared to normal mice, the alcoholic ones lacked behind in learning this new memory, although they eventually caught up. However, when both groups were shocked again with the tone (reinstatement), the alcoholics clearly showed greater freezing – meaning that the newly encoded extinction memory was not as strong or as easily recalled as the original fear memory . On the other hand, these alcoholic mice didn’t differ from their normal littermates in tests for general (non-tone related) anxiety, fear or motor performance, meaning that fear retention is specific to the tone.

So what mediates this behavior? Turning to the mPFC, researchers found that chronic alcohol remolded the shape of neurons, so that their dendrites were longer on the non-terminal branches on one side of the neurons. Since dendrites are the basic units of neuronal computation, and form dictates function, researchers went on to measure directly brain activity in the alcoholic mouse with electrodes. Chronic alcohol breathing decreased neuronal activity both during later periods of extinction and extinction retrieval, hinting that mPFC activity is greatly suppressed.  The authors went on to show that a type of receptor generally thought to be involved in learning and memory, the NMDA receptor, was also malfunctioning, giving lower currents than usual. In fact, by inhibiting just the NMDA receptor with a drug in normal mice, the researchers were able to mimic the extinction deficiency as seen in alcoholic mice.

This study suggests that chronic alcohol users if subjected to traumatic experiences, may be unable to efficiently deal with the associated fear and may be more at risk for developing anxiety disorders. While the study makes a good case for the dysfunction of mPFC in extinction deficits, it also begs the question: what about the hippocampus? Buried deep inside the brain, the hippocampus is long known to be the center of memory processing. Previous studies in brain slices (not animals) have also shown that alcohol exposure can inhibit NMDAR currents, so it’s conceivable that hippocampus is also playing a role. Another question that comes to mind is whether the perceived deficit in extinction is actually a deficit in “updating” the existing memory – that is, a decreased ability to flexibly learn and retain an opposite association when there is a similar memory present.

Regardless, this study adds to the pool of data that we currently have on the factors that predispose people to anxiety problems following traumatic experiences. While the study won’t make me give up on weekend happy hours, it might make me pause and think twice before I reach for that second bottle of weekday beer.

ResearchBlogging.org
Holmes A, Fitzgerald PJ, Macpherson KP, Debrouse L, Colacicco G, Flynn SM, Masneuf S, Pleil KE, Li C, Marcinkiewcz CA, Kash TL, Gunduz-Cinar O, & Camp M (2012). Chronic alcohol remodels prefrontal neurons and disrupts NMDAR-mediated fear extinction encoding. Nature neuroscience, 15 (10), 1359-61 PMID: 22941108