You all may recall that I posted recently about cocaine escalation in rats. Drugmonkey has also been posting some interesting stuff about addiction and…EXERCISE. And of course, Sci can’t see that and leave it alone. So I’m going back to a paper that really galvanized the idea of exercise in treating addiction.
Cosgrove, Hunter, Carroll. “Wheel-running attenuates intravenous cocaine self-administration in rats: Sex differences”. Pharmacology, Biochemistry, and Behavior, 2002.
The idea of using one type of reinforcer (when I use reinforcer in this post, I’ll be referring to a stimulus, in this case wheel running in rats, which, when you give it to the rat, increases the probability that the rat will try to get it again, using a learned response. This is different from reward in psychology and pharmacology, because in those fields, a reward is something that makes an animal approach it, NOT necessarily work for it. Complicated, I know).
Ok, that sentence got super long with the parentheses. Let’s try that again.
The idea of using one type of reinforcer to replace another one isn’t new. Pharmacologists have been looking for ages, using different reinforcers, to study in animals aspects of what makes cocaine (and other drugs, but in this case it’s cocaine) so addictive. Usually, the scientists will give the rat an option between cocaine and an artificial sweetener (you don’t want to use sugar because the rats get caloric benefit from that). But in this study, they wanted to look at the effects of exercise. They had seen some evidence that exercise in humans helped with quitting smoking, and they reasoned that exercise might be a good thing to use to get humans off drugs, since it’s not expensive (well, if you’re just running it’s not too bad), isn’t unhealthy (like chocolate or using other drugs), and isn’t a drug itself (which does work, but is expensive, requires a LOT of monitoring, and carries social stigma).
So they got some rats. They gave them running wheels. It might surprise some people who think of rats as kind of chubby and cuddly, but rats LOVE to run. LOVE. IT. If you give a rat a choice between a running wheel and food and it’s hungry…well the food actually doesn’t always win out.
So anyway. Rats. Wheels. They got to train on the wheels for two weeks. They then took away the wheels, put in catheters, and the rats were allowed to learn how to self-administer cocaine for five days. I’ve got several posts on how this works, but basically, you put a catheter into the rat’s back, and hook that up to a syringe filled with drug, which is on a pump connected to a lever. When the rat presses the lever, it turns on the pump for a specific period of time, and the pump pumps a little bit of cocaine into the rat’s vein. It’s a nice hit, as you might imagine.
So two weeks on the wheel, then the wheel was taken out. Five days training on the coke lever. Then the wheel was put back IN, and the rats were allowed access to both the wheel and the lever at the same time. And then they tested just the wheel and just the lever alone.
And the data speaks for itself:
BAM. LOOK at that set of bars on the left under female. That is some LOVELY behavioral data, that is. You can see that the female and male rats had different responses (which is REALLY interesting, but sadly they didn’t pursue that in this paper, I bet a paper on wheel running vs coke intake over the menstrual cycle would be totes awesome, but sadly I cannot find one). The male rats didn’t really reduce their cocaine intake when the running wheel was available (the grey bar in the set on the right), but the female rats REALLY did (the grey bar in the set on the left). Not only that, the far right bars in each set show that, without the wheel present, the cocaine consumption in both male and female rats goes right back to where it was before. It’s very clear that it’s the wheel running that lowering the cocaine consumption.
Here you can see the effect of the presence of coke on wheel running in the males and females. When the coke was present, their wheel running did decrease, as they now had to split their time (even though the females split their time a lot less and concentrated on wheel running). Then when they took the coke away, the wheel running went back to normal levels.
So it looks like running in rats can function as an alternative to doing cocaine, and means that there may be something to using exercise to decrease drug intake in humans (though this may be limited only to people who find they ENJOY exercise).
This study is really, really simple, but it also makes you think about WHY the rats are (a) reducing cocaine intake in the presence of a running wheel, and (b) doing the cocaine AT ALL. First, are they reducing coke intake when the wheel is around because they like the wheel more? Or is it because the wheel serves as a distraction, as something else to do? And if the wheel is serving as a distraction, are they only taking the cocaine because there isn’t much else to do? I don’t think this is true of humans, and so then you start to wonder what this says about cocaine self-administration in animals as a paradigm. There is nothing better for learning about drug addiction in animals than drug self-administration. But when you see results like this, you begin to wonder. It could very well be that exercise can help a great deal with drug addiction (and getting more exercise certainly wouldn’t hurt, at least). But could it also be that these animals aren’t as coke addicted as we thought?
Cosgrove, K. (2002). Wheel-running attenuates intravenous cocaine self-administration in rats Sex differences Pharmacology Biochemistry and Behavior, 73 (3), 663-671 DOI: 10.1016/S0091-3057(02)00853-5
