Cerebral glucose metabolism and D₂/D₃ receptor availability in young adults with cannabis dependence measured with positron emission tomography

Introduction: Cannabis users have been reported to have decreased regional cerebral glucose metabolism after short periods of abstinence. The purpose of this study was to measure striatal dopamine receptor (D₂/D ₃) availability and cerebral glucose metabolism with positron emission tomography (PET) in young adults who had a prolonged exposure to cannabis and who had been abstinent for a period of at least 12 weeks. Materials and methods: Six 18-21-year-old male subjects with cannabis dependence in early full remission and six age- and sex-matched healthy subjects underwent PET scans for D₂/D₃ receptor availability measured with [C11]-raclopride and glucose metabolism measured with [18F]-FDG. All subjects were sober for at least 12 weeks before PET scan procedures. PET data were analyzed with statistical parametric mapping software (SPM99; uncorrected p<0.001, corrected p<0.05 at the cluster level). Toxicology screening was performed prior to the PET scan to confirm the lack of drugs of abuse. Observation and results: Striatal D₂/D₃ receptor availability did not differ significantly between groups. Compared to controls, subjects with cannabis dependence had lower normalized glucose metabolism in the right orbitofrontal cortex, putamen bilaterally, and precuneus. There were no significant correlations between striatal D₂/D₃ receptor availability and normalized glucose metabolism in any region of the frontal cortex or striatum. Conclusion: These findings may reflect both cannabis exposure and adaptive changes that occur after a prolonged period of abstinence. Subsequent studies should address whether metabolic and dopamine receptor effects are associated with either active use or longer-term withdrawal in these relatively young subjects.