Preferential affinity of 3H-2-oxo-quazepam for type I benzodiazepine recognition sites in the human brain.
The hypnotic drug quazepam and its active metabolite 2-oxo-quazepam (2-oxo-quaz) are two benzodiazepines (BZ) containing a trifluoroethyl moiety on the ring nitrogen at position 1, characterized by their preferential affinity for Type I BZ recognition sites. In the present study we characterized the binding of 3H-2-oxo-quaz in discrete areas of the human brain. Saturation analysis demonstrated specific and saturable binding of 3H-2-oxo-quaz to membrane preparations from human cerebellum. Hill plot analysis of displacement curves of 3H-flunitrazepam (3H-FNT) binding by 2-oxo-quaz yielded Hill coefficients of approximately 1 in the cerebellum and significantly less than 1 in the cerebral cortex, hippocampus, caudate nucleus, thalamus and pons. Self and cross displacement curves for 3H-FNT and 3H-2-oxo-quaz binding in these brain areas indicated that 2-oxo-quaz binds with different affinities to two populations of binding sites. High affinity binding sites were more abundant in the cerebellum (95% of total sites), cerebral cortex, hippocampus and thalamus, whereas low affinity sites were predominant in the caudate nucleus and pons. Competition studies of 3H-2-oxo-quaz (2 nM) and 3H-FNT (0.5 nM) using unlabelled ligands indicated that compounds which preferentially bind to Type I sites are more potent at displacing 3H-2-oxo-quaz than 3H-FNT from cerebral cortex membrane preparations. The results suggest that 3H-2-oxo-quaz may be used for selectively studying Type I BZ recognition sites in the human brain.
D000328:Adult; D014151:Anti-Anxiety Agents / Q000378:metabolism* / Q000494:pharmacology; D001569:Benzodiazepines; D001570:Benzodiazepinones / Q000378:metabolism*; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D005260:Female; D005445:Flunitrazepam / Q000378:metabolism / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D008297:Male; D008875:Middle Aged; D009928:Organ Specificity; D011963:Receptors, GABA-A / Q000187:drug effects / Q000378:metabolism*
D014151:Anti-Anxiety Agents; D001570:Benzodiazepinones; D011963:Receptors, GABA-A; D001569:Benzodiazepines; D005445:Flunitrazepam; C039103:2-oxoquazepam