Benzodiazepine binding in human brain: Characterization using [³H] flunitrazepam

[3H]Flunitrazepam was used to characterize benzodiazepine binding sites in human brain. The benzodiazepine binding sites exhibited high affinity, pharmacological specificity and saturability in their binding of [3H]flunitrazepam. The dissociation constant (KD) of [3H]flunitrazepam binding was determined by three different methods and found to be in the range of 2-3 nM. The potency of several benzodiazepine analogs to inhibit specific [3H]-flunitrazepam binding in vitro correlated well with their potency in several in vivo human and animal tests. The density of [3H]-flunitrazepam binding sites was highest in the cerebrocortical and rhinencephalic areas, intermediate in the cerebellum, and lowest in the brain stem and commissural tracts.