Reproducibility of regional brain metabolic responses to lorazepam

Changes in regional brain glucose metabolism in response to benzodiazepine agonists have been used as indicators of benzodiazepine-GABA receptor function. The purpose of this study was to assess the reproducibility of these responses. Methods: Sixteen healthy right-handed men underwent scanning with PET and [¹⁸F]fluorodeoxyglucose (FDG) twice: before placebo and before lorazepam (30 μg/kg). The same double FDG procedure was repeated 6-8 wk later on the men to assess test-retest reproducibility. Results: The regional absolute brain metabolic values obtained during the second evaluation were significantly lower than those obtained from the first evaluation regardless of condition (p ≤ 0.001). Lorazepam significantly and consistently decreased both whole-brain metabolism and the magnitude. The regional pattern of the changes were comparable for both studies (12.3% ± 6.9% and 13.7% ± 7.4%). Lorazepam effects were the largest in the thalamus (22.2% ± 8.6% and 22.4% ± 6.9%) and occipital cortex (19% ± 8.9% and 21.8% ± 8.9%). Relative metabolic measures were highly reproducible both for pharmacologic and replication condition. Conclusion: This study measured the test-retest reproducibility in regional brain metabolic responses, and although the global and regional metabolic values were significantly lower for the repeated evaluation, the response to lorazepam was highly reproducible.