Study finds marijuana use leads to brain development in rats

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Saturday, October 15, 2005

In the November issue of the Journal of Clinical Investigation, researchers announce that they have found that cannabinoids promoted a generation of new neurons in rats' hippocampi. The study held true for both a plant-derived and a synthetic cannabinoid. The hippocampus is a part of the brain that contributes to learning and memory. In particular, it has been shown that the hippocampus is essential for the formation of new episodic memories.

"This is quite a surprise, chronic use of marijuana may actually improve learning memory when the new neurons in the hippocampus can mature in two or three months," said Xia Zhang, with the Neuropsychiatry Research Unit of the University of Saskatchewan.

"Our results were obtained from rats, and there's a big difference between rats and humans," added Zhang, "So, I really don't know yet if our findings apply to humans. But our results indicate that the clinical use of marijuana could make people feel better by helping control anxiety and depression."

Zhang and his co-workers performed behavioral tests on two purified cannabinoids. The test results indicated that these two cannabinoids have anti-anxiety and antidepression-like effects in rats that may depend on the ability of cannabinoids to promote the production of new neurons in the hippocampus. Marijuana contains a complex mixture of chemicals including cannabinoids and may have somewhat different behavioral effects than the purified cannabinoids tested so far.

Previous studies examining the effects of cannabis have highlighted negative aspects of the drug's use, such as short term memory difficulties, increased heart rate, nausea, and (in a very small percentage of people) hallucinations. Long term studies about cannabis use tend to be controversial as the data is seen to be biased or flawed. The most agreed upon effect of long term cannabis use is lung damage. However, proponents argue that the correlation between cannabis consumption and lung cancer is misleading suggesting that cannabis use may correlate with tobacco use or that the data is not being properly analyzed.

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"Cannabinoids promote embryonic and adult hippocampus neurogenesis and produce anxiolytic- and antidepressant-like effects" by Wen Jiang, Yun Zhang, Lan Xiao, Jamie Van Cleemput, Shao-Ping Ji, Guang Bai and Xia Zhang in Journal of Clinical Investigation (2005) doi:10.1172/JCI25509

. Available online Oct. 13, 2005 in advance of the journal's November print publication date.

"Marijuana may make your brain grow: Cannabinoid injections sprout new neurons in mice" by Geoff Brumfiel in Nature News Oct. 13, 2005 doi:10.1038/news051010-12

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Alan Mozes. "Marijuana Compound Spurs Brain Cell Growth" — HealthDay, Oct. 13, 2005

Dawn Walton. "Study turns pot wisdom on head" — Globe and Mail, Oct. 14, 2005

"Cannabis and Consequences" — Commonwealth of Australia, 2003

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