Cannabis use may lead to thinning of the cerebral cortex in adolescents according to a recent study led by and , according to a recent study led by Graciela Pineyro and Tomas Paus, researchers at CHU Sainte-Justine and professors at the Universit茅 de Montr茅al Faculty of Medicine. A collaborative effort between two research laboratories with complementary approaches, the study demonstrates that THC 鈥� or tetrahydrocannabinol, an active substance in cannabis 鈥� causes shrinkage of the dendritic arborization, neurons鈥� 鈥渘etwork of antennae鈥� whose role is critical for communication between neurons. This results in the atrophy of certain regions of the cerebral cortex 鈥� bad news at an age when the brain is maturing.
鈥淚f we take the analogy of the brain as a computer, the neurons would be the central processor, receiving all information via the synapses through the dendritic network,鈥� explains 罢辞尘补蝉鈥疨补耻蝉, who is also a professor of psychiatry and neuroscience at Universit茅 de Montr茅al. 鈥淪o a decrease in the data input to the central processor by dendrites makes it harder for the brain to learn new things, interact with people, cope with new situations, etc. In other words, it makes the brain more vulnerable to everything that can happen in a young person鈥檚 life.鈥�
A multi-level approach to better understand the effect on humans
This project is notable for the complementary, multi-level nature of the methods used. 鈥淏y analyzing magnetic resonance imaging (MRI) scans of the brains of a cohort of teenagers, we had already shown that young people who used cannabis before the age of 16 had a thinner cerebral cortex,鈥� explains 罢辞尘补蝉鈥疨补耻蝉. 鈥淗owever, this research method doesn鈥檛 allow us to draw any conclusions about causality, or to really understand THC鈥檚 effect on the brain cells.鈥濃��
Given the limitations of MRI, the introduction of the mouse model by 骋谤补肠颈别濒补鈥疨颈苍别测谤辞鈥檚 team was key. 鈥淭he model made it possible to demonstrate that THC modifies the expression of certain genes affecting the structure and function of synapses and dendrites,鈥� explains 骋谤补肠颈别濒补鈥疨颈苍别测谤辞, who is also a professor in the Department of Pharmacology and Physiology at Universit茅 de Montr茅al. 鈥淭he result is atrophy of the dendritic arborescence that could contribute to the thinning observed in certain regions of the cortex.鈥�
Interestingly, these genes were also found in humans, particularly in the thinner cortical regions of the cohort adolescents who experimented with cannabis. By combining their distinct research methods, the two teams were thus able to determine with a high degree of certainty that the genes targeted by THC in the mouse model were also associated to the cortical thinning observed in adolescents.
With cannabis use on the rise among North American youth, and commercial cannabis products containing increasing concentrations of THC, it鈥檚 imperative that we improve our understanding of how this substance affects brain maturation and cognition. This successful collaborative study, involving cutting-edge techniques in cellular and molecular biology, imaging and bioinformatics analysis, is a step in the right direction for the development of effective public health measures.
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