more negative than the reversal potential of GABAA receptor-mediated currents. In other words, activation of GABAA receptors may not change the membrane potential or even generate a depolarization and still reduce neuronal excitability. Membrane pumps, by setting intracellular Cl− concentration, play a critical role in regulating the reversal potential of GABAA receptor-mediated currents (Blaesse et al., 2009). In certain instances, for example in immature neurons (Ben-Ari et al., 2007) or in specialized neuronal compartments (Gulledge and Stuart, 2003; Szabadics et al., 2006; Woodruff et al., 2009), the reversal potential for Cl− is so depolarized that it may lead to an excitatory action of GABAA receptors. Although intriguing, still too little is known about how excitatory actions of GABA might impact processing in adult cortex to be discussed here.
