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Research Briefs—Nov. 18, 2014

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Long-term marijuana use on the brain

A study published in The Proceedings of The National Academy of Sciences last week has found that chronic—defined as three times per day over 10 years—marijuana users have a lower IQ score and smaller gray matter volume in the orbitofrontal cortex (OFC) region of the brain compared to non-users. However, the results also showed that marijuana users had higher functional and structural neural connectivity in the OFC. The study sampled from 48 chronic users and 62 non-users who were adjusted for gender, age, ethnicity, tobacco, and alcohol use; the study also excluded participants with histories or symptoms of neurological disorders, brain injuries, or psychosis.

The OFC is a region in the brain that is involved in emotion and reward in decision-making—frequently known as the reward centre of the brain. Consequently, the results of the  study show that the region of the brain involved in motivation based on a reward system shrink with long-term marijuana use, particularly for those who start at a young age.

Led by Francesca M. Filbey and her team out of the Center for BrainHealth at the University of Texas, the study showed that the brains of chronic users compensated for any shrinkage in the OFC by increasing connectivity between different areas of the brain, and increasing the structural integrity of tissues in the brain.

“[The results suggest] that there is definitely a more complicated pattern that the brain seems to be able to compensate for any kind of loss in order to keep that network maintained,” said Filbey in an interview with The Washington Post.

However, the study showed that this growth in connectivity and integrity continued for six to eight years, at which point the increased connectivity started to decline.

Although the study showed that the chronic marijuana users had lower IQ scores, the authors of the study clarified that these results had no correlation with a decrease in OFC volume.

“We did not find that the causal variable (i.e., marijuana use) was significantly correlated with the mediator variable [i.e., OFC gray matter volume] and outcome variable (i.e., IQ),” the study states.

Cannabinoids may shrink brain tumours

Cannabinoids, the active chemical compounds in cannabis, have been shown to induce tumour cell death by modifying faulty signalling pathways, according to a study released in Nature Reviews Cancer earlier this year. A new study published in Molecular Cancer Therapeutics has shown that tetrahydrocannabinol (THC) and cannabidiol (CBD)—two of the primary cannabinoids in cannabis—may be able to treat high-grade glioma, an aggressive brain cancer.

As with all cancers, high-grade glioma involves the rapid and uncontrollable growth of cancer cells, which usually results in tumours. The study—published by lead author Katherine A. Scott from the University of London—showed that a dosage of 2 milligrams each of pure THC and CBD per kilogram of body weight resulted in statistically significant reductions in tumour volumes (p < 0.01) when combined with irradiation cancer treatment.

The study involved an in vitro stage, as well as an orthotopic murine—rat and mice—model for glioma. However, the bulk of the study took place in vitro, which means that the experiment was primarily conducted in a Petri dish setting. Although the results of cannabinoids on high-grade glioma are promising, it is important to remember that in vitro tests do not necessarily translate to real effects in humans.

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