The GABAA-BZR complex as target for the development of anxiolytic drugs

Anxiety disorders have been linked to alterations in γ-aminobutyric acid (GABA) neurotransmission. GABA interacts with the ligand-gated ion channels, GABAA receptor (GABAA-R) subtypes, and regulates the flow of chloride into the cell, causing neuron hyperpolarization. GABAA-Rs are assembled from a family of 19 homologous subunit gene products and form mostly hetero-oligomeric pentamers. The major isoforms of the GABAA-Rs contain α, β and γ subunits and show a regional heterogeneity that is associated with distinct physiological effects. A variety of allosteric ligands can modulate the response to GABA by binding at different sites on the GABAA-R complex. The best characterized binding site is the benzodiazepine (BZ) one, which is located at the α/γ subunit interface. BZs are commonly used in therapy for their effects as anxiolytic, anticonvulsants, myorelaxants and hypnotics. The broad range of pharmacological effects of classical BZs are mediated by the selective activation of different GABAA-R subtypes: the α1 subunit containing BZ receptor (BZ-R) mediates sedation, the α2 and α3 subunit containing BZ-R mediates anxiolysis and myorelaxation, and the α5 subunit containing BZ-R mediates cognitive impairment. Based on the current understanding of the diversity of the GABAA-R family, different approaches have been employed to develop drugs that target the GABAA/BZ-R complex with selective anxiolytic action and improved profiles. In this review, we present current knowledge about the role of the GABAA/BZ-R complex in anxiety disorders, new insights into the molecular biology of the receptor complex, and the importance of this target in the development of new therapeutic agents in anxiety.