The Brain’s Own Marijuana

In the December, 2004 issue of Scientific American:
“The Brain’s Own Marijuana: Research into natural chemicals that mimic marijuana’s effects in the brain could help to explain–and suggest treatments for–pain, anxiety, eating disorders, phobias and other conditions” by Roger A. Nicoll and Bradley N. Alger

Marijuana is a drug with a mixed history. Mention it to one person, and it will conjure images of potheads lost in a spaced-out stupor. To another, it may represent relaxation, a slowing down of modern madness. To yet another, marijuana means hope for cancer patients suffering from the debilitating nausea of chemotherapy, or it is the promise of relief from chronic pain. The drug is all these things and more, for its history is a long one, spanning millennia and continents. It is also something everyone is familiar with, whether they know it or not. Everyone grows a form of the drug, regardless of their political leanings or recreational proclivities. That is because the brain makes its own marijuana, natural compounds called endocannabinoids (after the plant’s formal name, Cannabis sativa).

The authors have both been extensively involved in research in endocannabinoids, and they give a fascinating, though often technical, overview of how marijuana affects the brain, starting with a brief history of the use of marijuana worldwide and leading to the effects on specific parts of the brain.
One of the most interesting parts to me was the discussion on how the brain deals with stressful situations. Research has shown that repeated stimulus (like loud sounds) combined with stressful situations (like bullets whizzing at you) generates a natural fear reaction to the stimulus (in this case, loud sounds). In most people, after the stressful situation stops, gradually the stimulus fails to produce fear (so you’re not always jumping at loud sounds). Natural endocannabinoids are important in reducing the level of anxiety when the danger passes, but it’s believed that some individuals don’t produce them correctly, and you get no reduction of anxiety.
This is probably why the Israelis have looked into marijuana as a therapy for soldiers with post-traumatic stress disorder, and it leads to all sorts of potential uses of marijuana for psychological treatments.
The authors conclude:

In a remarkable way, the effects of marijuana have led to the still unfolding story of the endocannabinoids. The receptor CB1 seems to be present in all vertebrate species, suggesting that systems employing the brain’s own marijuana have been in existence for about 500 million years. During that time, endocannabinoids have been adapted to serve numerous, often subtle, functions. We have learned that they do not affect the development of fear, but the forgetting of fear; they do not alter the ability to eat, but the desirability of the food, and so on. Their presence in parts of the brain associated with complex motor behavior, cognition, learning and memory implies that much remains to be discovered about the uses to which evolution has put these interesting messengers.