Demonstration of [3H] diazepam binding to benzodiazepine receptors in vivo.

Benzodiazepine receptors were labeled with ³H] diazepam following intravenous injection in rats. Binding of ³H] diazepam $\text{in}$$\text{vivo}$ to rat forebrain membranes was displaceable by co-injection of clonazepam or the pharmacologically active enantiomers of two benzodiazepines, B9 and B10, but was not displaced by equal doses of the pharmacologically in-active enantiomers. Binding of ³H] diazepam $\text{in}$$\text{vivo}$ was bserved in kidney, liver, and abdominal muscle, but was not stereospecifically diplaced in any peripheral tissue studied. The regional distribution of benzodiazepine receptors in brain was uneven, with specific ³H] diazepam binding being highest in the cerebral cortex and lowest in the ponsmedulla. Preliminary studies of the subcellular distribution of ³H] diazepam binding demonstrated highest specific binding to synaptosomal membranes. These data demonstrate the feasibility of labeling benzodiazepine receptors in rat brain $\text{in}$$\text{vivo}$.