Benzodiazepines in perspective (II): The GABAA-Benzodiazepine Receptor Ligands.

A huge number of natural and synthetic compounds modulate the function of the γ-aminobutyric acid type A receptor (GABAA-R) by interacting with several allosteric binding sites which may differ in the various GABAA-R subtypes. The benzodiazepine receptor (BDZ-R) is the most intensively studied allosteric site. It is the first allosteric modulatory site on a neurotransmitter receptor that has been found to mediate two opposite functions: facilitation and depression of GABAA-R function. The effects of BDZ-R ligands on behavior range from agonistic (anxiolytic, anticonvulsant, myore-laxant/ataxic and hypno-sedative effects) to inverse-agonistic (anxiety and panic, hypervigilance and convulsions). Of particular interest for the future are BDZ-R partial agonists, as they lack several of the undesired properties of classic full agonists. Furthermore the GABAA-R system shows a high plasticity. This polymorphism raises the possibility that ligands selective for distinct subtypes of BDZ-R may emerge as useful drugs. In both cases the possibility exists of achieving very subtle manipulations of GABAA-R function by using allosteric modulators.