Binding sites for [3H]2-oxo-quazepam in the brain of the cat: evidence for heterogeneity of benzodiazepine recognition sites.

In the present study, the distribution of benzodiazepine recognition site subtypes in the brain of the cat was investigated. To this aim, the binding properties of [3H]2-oxo-quazepam ([3H]2OXOQ) and [3H]beta-CCE, two ligands with preferential affinity for Type I benzodiazepine recognition sites, were compared to binding parameters for [3H]flunitrazepam ([3H]FNT) in different areas of the cat brain. The ratio of [3H]2OXOQ to [3H]FNT binding sites indicated that, in the cerebellum, Type I sites accounted for 90% of the total number of benzodiazepine recognition sites. The cerebral cortex, thalamus and mesencephalic reticular formation had also a high proportion of Type I sites (73-78%), whilst the two subtypes were almost equally distributed in the hippocampus, amygdala and bulbar reticular formation. A similar distribution of subtypes of benzodiazepine recognition sites was indicated by the ratio of [3H]beta CCE to [3H]FNT binding sites for different areas of the brain. These results demonstrate the existence of heterogeneity of recognition sites for benzodiazepines in the brain of the cat and support the view that [3H]2OXOQ preferentially labels Type I sites.