Molecular mechanisms of antiseizure drug activity at GABAA receptors

The GABA(A) receptor (GABA(A)R) is a major target of antiseizure drugs (ASDs). A variety of agents that act at GABA(A)Rs s are used to terminate or prevent seizures. Many act at distinct receptor sites determined by the subunit composition of the holoreceptor. For the benzodiazepines, barbiturates, and loreclezole, actions at the GABA(A)R are the primary or only known mechanism of antiseizure action. For topiramate, felbamate, retigabine, losigamone and stiripentol, GABA(A)R modulation is one of several possible antiseizure mechanisms. Allopregnanolone, a progesterone metabolite that enhances GABA(A)R function, led to the development of ganaxolone. Other agents modulate GABAergic "tone" by regulating the synthesis, transport or breakdown of GABA. GABA(A)R efficacy is also affected by the transmembrane chloride gradient, which changes during development and in chronic epilepsy. This may provide an additional target for "GABAergic" ASDs. GABA(A)R subunit changes occur both acutely during status epilepticus and in chronic epilepsy, which alter both intrinsic GABA(A)R function and the response to GABA(A)R-acting ASDs. Manipulation of subunit expression patterns or novel ASDs targeting the altered receptors may provide a novel approach for seizure prevention. (C) 2013 British Epilepsy Association. Published by Elsevier Ltd. All rights reserved.