Specificity within the GABAA receptor supramolecular complex: a consideration of the new omega 1-receptor selective imidazopyridine hypnotic zolpidem

The relative contribution of different recognition sites within the GABAA receptor supramolecular complex (GRSC) to the pharmacological effects of anxiolytic and hypnotic drugs is unknown. The development of the omega 1 (ex BZ1) specific hypnotic zolpidem allows a more direct approach to the problem. In contrast to many benzodiazepine hypnotic/anxiolytics (e.g., flunitrazepam, diazepam), zolpidem shows a specificity for GABAergic function, e.g., selectively reversing isoniazide-induced seizures. Furthermore, zolpidem produces a highly specific hypnotic action as compared to myorelaxant or amnesic effects (ratio of ED50's greater than 4.0 for zolpidem; less than 1 for flunitrazepam). Zolpidem exerts its action within the GRSC as it enhances 35S-TBPS binding, as do mixed omega 1/omega 2 compounds or GABA agonists. Both the in vivo and in vitro actions of zolpidem are reversed by flumazenil and the enhanced 35S-TBPS binding is also bicuculline-sensitive. Thus, omega 1 recognition site stimulation (e.g., by zolpidem) is sufficient to produce potent pharmacological effects and modulation of the GABAA receptor-gated chloride ionophore.