Those of us who study natural reward systems, like those involved in feeding and drinking, are often welcome at parties of people who study drug addiction. For many drugs of abuse, a common way of thinking about how they work, at least at first, is by targeting these same reward systems, but bypassing the stuff that “naturally” activates them. So instead of getting a little activation of the system by eating a piece of chocolate, you get a big activation from cocaine.
For many drugs of abuse, this “bypassing” effect is more or less intuitive. Drugs like cocaine and heroin seem to bypass the normal route to particular systems in the brain, and go right to the source. The source, in this way of thinking, is a very important part of our normal systems. It didn’t evolve to respond to drugs. We don’t have a natural system for responding to these drugs. Instead, we have these systems so that we eat, drink, have sex…do the things that are necessary for our survival (as individuals and a species).
For other drugs, that “natural” system isn’t as clear. Nicotine is a complicated one, for instance, but seems to tap into our important ability to make associations between things with value and things that signal that value. What does this mean in simple terms? If you’re a smoker, you know that if feels good to fill your lungs with the smoke from a cigarette. If you’re not a smoker, that just sounds crazy. How can smoke in your lungs feel good? Well, it likely didn’t the first time, or few times, you smoked, but the nicotine in the smoke promoted a positive association between the smoke and the drug, making the smoke feel great. So how does that work “naturally”? Imagine there’s a pricker bush that has an excellent source of nutrition if you can just get through the outside part that hurts your hands a bit. Without the “natural” system that nicotine might tap into, you might never get past the negative part of the prickers and learn that the bush is a great source of food for you to stay alive. Some scientists studying these things have come to believe that this system, the system that makes otherwise mundane things become a symbol of goodness, is what nicotine taps into.
Then there’s tetrahydrocannabinol, THC, the chemical in the marijuana plant that produces the effect from smoking pot (am I showing my age by calling it that?). There’s some evidence that this system eventually feeds into the same system that makes us like eating, drinking, having sex, etc, but it’s not as simple as that, and it seems to work in a lot of different ways. That’s where the running comes in. For a long time, if you asked people what causes runner’s high, they would say endorphins. This comes from earlier studies showing high levels of endorphins in the blood of runners. There were some problems with these findings though. First, with closer looks, the level of endorphins in the blood didn’t seem to correlate with the subjective experience of runners high. Second, endorphins in the blood don’t have a good way to get to the brain, and a feeling of being “high” most likely requires action at the brain. Unless the endorphins worked on the brain indirectly, they most likely weren’t the source of the “high” that some runners report. That’s where THC, or at least the substance similar to THC that’s made in our very own bodies comes in, and that’s the topic of the article in the New York Times that inspired this post.
The article is here: http://nyti.ms/1jNFhhc
What the article doesn’t talk about is how this fits into a natural system. What then, is THC acting on when it’s taken recreationally? Well, it’s not to hard to imagine that part of our evolutionary history involved travelling long distances on foot. It’s not hard to imagine that individuals who had a mechanism that made this tolerable, even pleasurable, wouldn’t have an advantage over those who didn’t. It’s not hard to imagine that individuals with this system would be less likely to be eaten by predators, and more likely to get to a safe place first and have a better chance of reproducing. So, it’s possible to speculate that in the same way that cocaine bypasses the things (eating, drinking) that normally get to its target, smoking pot bypasses the running to get to the high. Runner’s high without the running. Of course this is mostly speculation…for now.
Thirst Science 