Scientific American has a great article this month on the relationship of cannabioids, endocannabinoids, and long term pain memories and lots of other stuff about this important class of chemicals in the functioning of the brain.
Recent discoveries have also begun to precisely link the neuronal effects of endocannabinoids to their behavioral and physiological effects. Scientists investigating the basis of anxiety commonly begin by training rodents to associate a particular signal with something that frightens them. They often administer a brief mild shock to the feet at the same time that they generate a sound.Another study from the Max Plack Institute suggested this might be the case as well. I reported on it in August of 2002. At the time I was really excited because I thought that based on other stuff I had found that the keys to chronic drug use (what is often mistakenly called addiction) were being given to us. I discussed it here as well as here. It looks like I'm going to be vindicated sooner rather than later. Although we probably still have some ways to go.
After a while the animal will freeze in anticipation of the shock if it hears the sound. If the sound is repeatedly played without the shock, however, the animal stops being afraid when it hears the sound--that is, it unlearns the fear conditioning, a process called extinction. In 2003 Giovanni Marsicano of the Max Planck Institute of Psychiatry in Munich and his co-workers showed that mice lacking normal CB1 readily learn to fear the shock-related sound, but in contrast to animals with intact CB1, they fail to lose their fear of the sound when it stops being coupled with the shock.
The results indicate that endocannabinoids are important in extinguishing the bad feelings and pain triggered by reminders of past experiences. The discoveries raise the possibility that abnormally low numbers of cannabinoid receptors or the faulty release of endogenous cannabinoids are involved in post-traumatic stress syndrome, phobias and certain forms of chronic pain. This suggestion fits with the fact that some people smoke marijuana to decrease their anxiety. It is also conceivable, though far from proved, that chemical mimics of these natural substances could allow us to put the past behind us when signals that we have learned to associate with certain dangers no longer have meaning in the real world.
Joe Katzman at Winds of Change has some thoughts.