Regulation of GABA(A) receptor subunit expression by pharmacological agents.

The gamma-aminobutyric acid (GABA) type A receptor system, the main fast-acting inhibitory neurotransmitter system in the brain, is the pharmacological target for many drugs used clinically to treat, for example, anxiety disorders and epilepsy, and to induce and maintain sedation, sleep, and anesthesia. These drugs facilitate the function of pentameric GABA(A) receptors that exhibit widespread expression in all brain regions and large structural and pharmacological heterogeneity as a result of composition from a repertoire of 19 subunit variants. One of the main problems in clinical use of GABA(A) receptor agonists is the development of tolerance. Most drugs, in long-term use and during withdrawal, have been associated with important modulations of the receptor subunit expression in brain-region-specific manner, participating in the mechanisms of tolerance and dependence. In most cases, the molecular mechanisms of regulation of subunit expression are poorly known, partly as a result of neurobiological adaptation to altered neuronal function. More knowledge has been obtained on the mechanisms of GABA(A) receptor trafficking and cell surface expression and the processes that may contribute to tolerance, although their possible pharmacological regulation is not known. Drug development for neuropsychiatric disorders, including epilepsy, alcoholism, schizophrenia, and anxiety, has been ongoing for several years. One key step to extend drug development related to GABA(A) receptors is likely to require deeper understanding of the adaptational mechanisms of neurons, receptors themselves with interacting proteins, and finally receptor subunits during drug action and in neuropsychiatric disease processes.