Altered white matter microstructure in adolescent substance users

Chronic marijuana use during adolescence is frequently comorbid with heavy alcohol consumption associated with CNS alterations, yet the influence of early cannabis and alcohol use on microstructural matter integrity is unclear. Building on evidence that cannabinoid receptors are present in myelin and affect glial cell processing, and that excessive ethanol exposure is associated with persistently myelination, we used diffusion tensor imaging (DTI) to characterize white matter integrity in heavy using and non-using adolescents. We evaluated 36 marijuana and alcohol-using (MJ + ALC) adolescents (ages 16-19) and 36 demographically similar non-using controls with DTI. The diffusion parameters anisotropy (FA) and mean diffusivity (MD) were subjected to whole-brain voxelwise group comparisons tract-based spatial statistics (Smith, S.M., Jenkinson, M., Johansen-Berg, H., Rueckert, D., Nichols, T.E., C.E., Watkins, K.E., Ciccarelli, O., Cader, M.Z., Matthews, P.M., Behrens, T.E., 2006. Tract-based spatial voxelwise analysis of multi-subject diffusion data. Neuroimage 31, 1487-1505). MJ+ALC teens significantly lower FA than controls in 10 regions, including left superior longitudinal fasciculus (SLF), postcentral gyrus, bilateral crus cerebri, and inferior frontal and temporal white matter tracts. diminutions occurred in the context of increased FA in right occipital, internal capsule, and SLF Changes in MD were less distributed, but increased MD was evident in the right occipital lobe, whereas the inferior longitudinal fasciculus showed lower MD in MJ + ALC users. Findings suggest that circuitry may be particularly impacted in adolescent users of the most prevalent intoxicants: marijuana alcohol. Disruptions to white matter in this young group could indicate aberrant axonal and maturation with resultant compromise of fiber integrity. Findings of increased anisotropic diffusion alternate brain regions suggest possible neuroadaptive processes and can be examined in future studies connectivity to determine how aberrancies in specific tracts might influence efficient cognitive (C) 2009 Elsevier Ireland Ltd. All rights