marijuana, anxiety, and memory

A recent study that's gotten a bit of press suggests that marijuana-like compounds may aid in depression and anxiety. Some researchers in Saskatoon examined the effects of a synthetic cannabinoid (like THC but much stronger) on a part of the brain called the hippocampus, in mice. They found that the chemical causes new neurons to grow in the hippocampus, similar to the way anti-depressants work. That's interesting, of course, since marijuana is a drug often used by people with anxiety or depression to self-medicate themselves. (Modern SSRIs and therapy work rather better at treating these disorders than smoking weed, it should be noted...) The implication, then, is that some version of cannabinoids might be another approach to treating depression in the future.

OK, perhaps, but it should be noted that the hippocampus is also a major center for the encoding of new memories, which is why heavy use of marijuana causes short-term memory impairment. It would be very interesting if this coincides with an increase in the number of neurons. Usually, one would associate an increase in neurons with an increase in memory capacity. But perhaps not in this case. It should also be noted that, somewhat paradoxially, marijuana seems to slow memory loss in Alzheimer's patients.

I will be exceedingly interested to find out how this all resolves. Perhaps high doses of cannabinoids cause growth of new hippocampal neurons, which temporarily disrupts the encoding of new memories, but then can be used later on once those neurons are fully integrated into the network? And does this process cause a reduction in anxiety and depression, or are they independent effects of the drug?