Benzodiazepine receptor binding of benzodiazepine hypnotics: receptor and ligand specificity

Benzodiazepine (BDZ) hypnotics bind at a specific receptor located on postsynaptic neurons. Some data support specificity of binding for several hypnotics to receptor subtypes. We evaluated BDZ receptor binding in cerebral cortical membranes using agonist, antagonist, and subtype-specific ligands for commonly used hypnotics and their metabolites. All hypnotics competed similarly at BDZ1 and BDZ2 receptor subtypes except quazepam and its metabolite 2-oxo-quazepam and to a lesser extent hydroxyethyl flurazepam (EtOH) flurazepam. These compounds had relative specificity for the BDZ1 site. Triazolam, estazolam, and flurazepam bound equally to sites labeled by agonists and antagonists but desalkylflurazepam, EtOH flurazepam, temazepam, quazepam, and 2-oxo-quazepam did not; in addition, these four compounds did not bind to the "peripheral" BDZ site labeled by Ro 5-4864. BDZ hypnotics differ in their receptor subtype and ligand binding characteristics.