Detection of benzodiazepine receptor occupancy in the human brain by positron emission tomography

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Abstract
Benzodiazepine receptor occupancy in the brain following oral administration of clonazepam (CZP) with a dose of 30 μg/kg in six healthy young men and a further dose of 50 μg/kg in one of the subjects was estimated by carbon-11 labeled Ro15-1788 and positron emission tomography (PET). The effects of CZP on the latency of auditory event-related potentials (P300) were also studied. Overall brain 11C uptake was depressed and the % inhibition of 11C uptake in the gray matter of the brain at 30 min after [11C]Ro15-1788 injection was 15.3–23.5% (mean, n=6) following 30 μg/kg CZP when compared with that in the control experiment without any previous treatment. The 11C uptake in the cerebral cortex in the subject who received both doses decreased in a dose-related manner after 30 μg/kg and 50 μg/kg CZP. The P300 latency was prolonged significantly by 30 μg/kg CZP [31.6±16.3 ms (mean±SD, n=6), P11C]Ro15-1788 and PET permits comparison of the pharmacological effects with the percentage of receptor sites which benzodiazepines occupy in the human brain. P300 also seems to be useful to investigate the pharmacological effects of benzodiazepines.