A previous study showed that the antidepressant fluoxetine (Prozac) also increases new cell growth, and the results indicated that it was this cell growth that caused Prozac’s anti-anxiety effect. Zhang wondered whether this was also the case for the cannabinoid, and so he tested the rats for behavioural changes.
A synthetic chemical similar to the active ingredient in marijuana makes new cells grow in rat brains. What is more, in rats this cell growth appears to be linked with reducing anxiety and depression. The results suggest that marijuana, or its derivatives, could actually be good for the brain.
Just like Prozac?
In another study, Barry Jacobs, a neuroscientist at Princeton University, gave mice the natural cannabinoid found in marijuana, THC (D9-tetrahydrocannabinol)). But he says he detected no neurogenesis, no matter what dose he gave or the length of time he gave it for. He will present his results at the Society for Neuroscience meeting in Washington DC in November.
When the rats who had received the cannabinoid were placed under stress, they showed fewer signs of anxiety and depression than rats who had not had the treatment. When neurogenesis was halted in these rats using X-rays, this effect disappeared, indicating that the new cell growth might be responsible for the behavioural changes.
Jacobs says it could be that HU210 and THC do not have the same effect on cell growth. It could also be the case that cannabinoids behave differently in different rodent species – which leaves open the question of how they behave in humans.
“These complicated effects of high and low doses of acute and chronic exposure to cannabinoids may explain the seemingly conflicting results observed in clinical studies regarding the effects of cannabinoid on anxiety and depression,” the scientists say.
Experiments on rats given a potent cannabinoid have shown the drug stimulates the growth of new brain cells. Canadian researchers found that the drug caused neurons to regenerate in the hippocampus, an area that controls mood and emotions, after one month of treatment.
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The experiment involved giving rats regular injections of HU210 for a month. At the end of this time, hungry animals showed significantly less reluctance to eat in a novel environment. Rats are normally neophobic – wary of new situations.