Selective affinity of the benzodiazepines quazepam and 2-oxo-quazepam for BZ1 binding site and demonstration of H-2-oxo-quazepam as a BZ1 selective radioligand

Quazepam and 2-oxo-quazepam are novel benzodiazepines containing a trifluoroethyl substituent on the ring nitrogen at position number1. Detailed competition binding experiments (25 to 30 concs.) at 40C were undertaken with these compounds versus 3H-flunitrazepam using synaptic membranes from rat cortex or cerebellum. Unlike other benzodiazepines, both quazepam and 2-oxo-quazepam distinguished two populations of 3H-flunitrazepam binding sites in rat cortex which were present in roughly equal proportions and for which the compounds displayed a greater than 20-fold difference in affinity. In cerebellum, no such discrimination of sites was noted for 2-oxo-quazepam, but quazepam did distinguish a small, low affinity population of sites. 3H-2-oxo-quazepam was prepared and used in competition studies to substantiate the conclusion that these compounds discriminate two populations of benzodiazepine sites in rat cortex. This new radioligand was shown to specifically label BZ binding sites with high affinity in a saturable manner. The competition experiments were then conducted using 3H-2-oxo-quazepam at a radioligand concentration sufficiently low to ensure that only the higher affinity binding sites which 2-oxo-quazepam discriminates would be occupied. 15 references, 3 figures, 4 tables