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Cannabis Campaigners' Guide News Database result:
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Pot May Not Shrink Teens' Brains After All
Neil Osterweil, Senior Associate Editor, MedPage Today MedPage Today
Monday 08 May 2006 MedPage Today Action Points Explain to interested patients that the authors of this study used a sophisticated imaging technique to compare specific brain areas in young adults who were frequent users of marijuana in their teens with those of non-users, and found no evidence that marijuana uses adversely affects the brain structures studied. Explain that the results are preliminary and need to be confirmed in larger studies. Review ORANGEBURG, N.Y., May 8 — The notion that marijuana induces growing brains to atrophy didn't hold up when tested by a new MRI technique, researchers have reported. Using diffusion tensor imaging to compare the brains of teenagers who reported smoking marijuana moderately with those who didn't, the investigators found no evidence that pot damages or changes growing adolescent brain. "These data lead to the likely conclusion that cannabis use, in at least moderate amounts, during adolescence does not appear to be neurotoxic, although we cannot exclude any adverse effects of heavier amounts than that used by the current subjects," wrote Lynn E. DeLisi, M.D., of the Nathan S. Kline Institute for Psychiatric Research, here, and colleagues at New York University. "These data are preliminary and need replication with larger numbers of subjects, although they do have implications for refuting the hypothesis that cannabis alone can cause a psychiatric disturbance such as schizophrenia by directly producing brain pathology," said Dr. DeLisi and colleagues in the open-access online publication Harm Reduction Journal. A controversial report published in the Lancet in 1971 suggested that marijuana use is associated with cerebral atrophy, but subsequent brain imaging studies with CT and MRI have not backed it, the authors noted. "Since cannabis use changes the density of cannabinoid -1 receptors in the brain, it is possible that this density alteration could be associated with volume loss as detectable by MRI in cannabinoid receptor-rich brain regions, such as temporal cortex," they wrote. To evaluate possible cannabis-induced neurotoxicity in still-developing brains, the researchers took advantage of the recently developed MRI technique diffusion tensor imaging, which relies on the diffusion of water (so-called Brownian motion) to delineate with greater precision the white matter of the brain. The measures used include apparent diffusion coefficient, which may relate to and fractional anisotropy; decreases in fractional anisotropy are thought to correlate with white matter damage. In this preliminary study, the authors performed analyses on MRI scans of the brains of nine young men and one young woman (mean age 21 years range, 18-27) who were frequent marijuana users in their teens, and of age- and sex-matched controls who never used pot. They used the diffusion tensor imaging technique to look for cerebral atrophy and white matter integrity. They also measured whole brain volumes, lateral ventricular volumes, and gray matter volumes of the amygdala-hippocampal complex, superior temporal gyrus, and entire temporal lobes (excluding the amygdala-hippocampal complex). They found that "while differences existed between groups, no pattern consistent with evidence of cerebral atrophy or loss of white matter integrity was detected." Specifically, they found no significant changes in any measured brain structures in the marijuana users versus controls. However, on a voxel-by-voxel analysis, they found that there were two regions where the apparent diffusion coefficient was reduced in cannabis users relative to non-users, and six regions where the fractional anisotropy was increased among pot users. "Regions of higher apparent diffusion coefficient, putative evidence of atrophy, were not present, although regions of significantly lower apparent diffusion coefficient were," Dr. DeLisi and colleagues wrote. "While low fractional anisotropy would be indicative of less white matter integrity, particularly with respect to fiber direction, all fractional anisotropy differences in this study were higher values in cannabis users than non-users." http://www.medpagetoday.com/Neurology/GeneralNeurology/tb/3242
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