Did you know that you have an endocannabinoid system in your body? If not, don't worry - neither did anyone else until the 1990s. You may have noticed, from its name, that it has something to do with cannabis. The active component of cannabis (THC) produces its effect by disrupting this system, but that's not what the system is there for!
In a nutshell...
This is a system which is comprised of two main endocannabinoids - these are molecules, which happen to be called AEA and 2-AG. Then, there are two key receptors - called CB1 and CB2 - which the endocannabinoids bind to, like a key fitting into a lock. When they bind with one of these receptors on a brain cell they suppress the release of neurotransmitters - the chemicals used by brain cells to communicate with each other. This is how the endocannabinoid system works to affect brain function and, in turn, a whole host of effects that we'll look at now.
So, what does the endocannabinoid system do?
Firstly, it's important for creating new connections between brain cells and strengthening important existing connections that you use a lot. On the flip side, it is also used to get rid of connections between brain cells that are no longer needed - like doing a Disk Cleanup on your computer so that it operates more efficiently. This whole process is called neural plasticity - it helps your brain to adapt physically to your experiences.
This is important for all kinds of reasons but especially because when neuroplasticity is disrupted, especially in response to stress, you are more likely to experience depression and anxiety. Conversely, when you boost the levels of the AEA endocannabinoid you can get results which are similar to administering anti-anxiety medication (at least in rats). And when you reduce levels of the 2-AG endocannabinoid it increases levels of anxiety (at least in mice).
However, if you're not impressed by all these animal study findings, one minute with someone who has voluntarily activated their endocannabinoid system (by getting stoned) will show you that the effect is to make that person pretty relaxed. The problem with this type of self-medication is that it comes with all kinds of side effects. Endocannabinoids, on the other hand, are produced naturally by the body and have no such draw-backs.
The second key function of the endocannabinoid system is that, as well as helping with neuroplasticity, it has a direct effect on your stress response. When you experience something stressful, you produce endocannabinoids which regulate and dampen the physiological stress response, which again helps reduce the experience of anxiety. Specifically, AEA seems to keep a check on the activation and intensity of your biological stress response, whereas 2-AG is involved in effectively calming your body down after a stressful event, bringing everything back to normal.
What's even better is that the endocannabinoid system learns from experience and produces increasingly high levels of endocannabinoids in repeated occurrences of the same stressor, so you become increasingly effective at dealing with it calmly.
Finally, related to all of this, endocannabinoids are used for effective memory formation, especially in the hippocampus. But perhaps more amazingly, they help to prevent the formation and retrieval of harmful, traumatic memories. This means that when the endocannabinoid system is disrupted it can lead to negative memory bias.
That sounds great - can I get more endocannabinoids to boost my system?
Well, yes you can.
Firstly, you could sing. That seems to increase the level of AEA by over 40%.
Secondly, you can move. For example, moderate levels of exercise have been found to increase levels of circulating endocannabinoids (low intensity and high intensity exercise did not work). To give you an idea of what it looks like, moderate exercise can be defined as very brisk walking, heavy-duty cleaning (washing windows or vacuuming), mowing the lawn, light-effort bicycling (10-12 mph), recreational badminton and tennis doubles.
In terms of how duration, a single session of moderate exercise at 30, 50 and 90 minutes has been found to significantly increase endocannabinoids. And this works under field conditions as well as in the lab. Interestingly, all of these studies looked at aerobic exercise and found that it was only AEA which was increased. There is one study, however, which looked at very short bursts of strength training, rather than aerobic exercise. This study found that 3 minutes of isometric contractions increased not only AEA but also the other endocannabinoid, 2-AG.
It's still early days in finding out about the exact effect of exercise on the endocannabinoid system, but what this research suggests is that different types of exercise are going to effect endocannabinoids in different ways.
Postscript: Endocannabinoids and BDNF
Finally, there seems to be an interesting link between the endocannabinois system and BDNF, which I've already discussed here. For example, when you measure both AEA and BDNF during exercise you find a positive correlation - as the level of one of them goes up, so does the other. And it seems as though it's the increasing level of endocannabinoids which causes the increase in BDNF. So maybe exercise increases endocannabinoids and these then increase BDNF.