Chewing to take the stress away

May 30 2012 Published by under Behavioral Neuro

Not you chewing. The rats.

Why chewing, you might ask? The authors of this study are using chewing as a way to induce "active behavioral coping". And while the idea has merit, the data make me not so sure.

Helmreich et al. "Active behavioral coping alters the behavioral but not the endocrine response to stress" Psychoneuroendocrinology, 2012.

Look, we all know stress is bad for you. Stressors (scientists define these as anything that is aversive and uncontrollable or unpredictable) produce a lot of short and long term effects on the body, as well as effects on behavior. Stress increases the "stress hormone" cortisol (corticosterone in rodents), increases anxiety like behaviors, can change depressive-like behaviors, and can even have effects on things like cell proliferation in the brain.

With all of these negative effects, we want to find ways to combat stressors, or at least to blunt them. One way to try and blunt the effects of a stressor is something called "active coping". Behavioral coping, or the way that animals try to deal with surrounding stress, can be divided into active (say, actively trying to escape the stress), and passive (just taking it). Active behavioral coping can occur spontaneously or be manipulated in (an animal may be able to stop the stressor, for instance), and can help moderate the effects of stress.

The best example of this is escapable shock. You have a rat, and you give it a series of aversive shocks in its cage (not enough to harm the rat, but stressful). You then give the rat an opportunity to escape the stressor, say by turning a wheel or pressing a lever that turns the shock off. The rat will go for it (active coping). The rat is still stressed, but the behavioral effects of stress are reduced.

So that's escapable stress, what does chewing have to do with it? The authors of this study wanted to look at whether chewing something could help rats cope actively with a stressor. Rats are natural chewers, so it might help them to deal. They set up rats with a shock, and a chewing rod (made of wood). They checked for chewing (by recording the sound from the animal's cage, though I imagine you could just look). They then looked to see how the rats responded to stress.

What you can see here are various behavioral tests for social exploration and open field behavior, measures of anxiety in rats. Rats with inescapable shock showed more anxiety, but those with a wooden rod to chew on looked more like controls (at least, where they showed controls, I'll get to that later).

But what's interested is that, although the behavior is better, the corticosterone response remains the same:

You can see that chewing had no effect on corticosterone response or on changes in thyroid hormones (which also respond to stress).

The authors conclude that the chewing is an active coping mechanism and helps the behavioral response to the stressor because of the active coping.

I'm not so sure I agree with this interpretation. First off, there are some issues with the data. Two of the behavioral tests have no home cage control group, which I would really like to see before I determine how much better or worse a test group is. Secondly, while these are anxiety-like responses in rats, I would like to see more, say depression-like responses in the forced swim test, or changes in neurogenesis with the inescapable shock that is normalized by the chewing. I would also really like to see this "active coping" compared fully with the escapable shock routine, which they only used in their thyroid hormone measures. If you're going to claim another active coping mechanism, you really need to compare it to a known one to convince me.

Finally, is this really active coping? Or are the behavioral effects something else? I personally wonder if the effects of chewing here might be similar to the effects of, say, exercise, which changes the behavior and cell proliferation effects of stress as well. Not only that, active coping usually requires control over your environment (turning a wheel to stop the stressor, for instance). Chewing doesn't have any effect on the environment, so can we really call it an active coping mechanism? I don't think we can.

So the next time you're feeling stressed, I don't think chewing gum will make you feel any better (though it might if you like it, you never know!), and this study isn't convincing me otherwise.

Helmreich, D., Tylee, D., Christianson, J., Kubala, K., Govindarajan, S., O’Neill, W., Becoats, K., Watkins, L., & Maier, S. (2012). Active behavioral coping alters the behavioral but not the endocrine response to stress Psychoneuroendocrinology DOI: 10.1016/j.psyneuen.2012.04.005

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