Extrasynaptic receptors have been identified also in other brain regions. In the forebrain it is assumed that they are predominantly composed of α4βδ. Experiments indicating that tonic conductance sometimes can also be enhanced by benzodiazepines suggest that tonic inhibition can also be produced by gamma subunit-containing receptors. In the forebrain evidence has accumulated that such receptors might be composed of α5βγ2 subunits. But it can be assumed that receptors with other subunit composition also can occur extrasynaptically (Semyanov et al., 2004). Due to the much larger cell surface area, the charge carried by the activation of tonically active GABAA-R can be more than three times larger than that produced by phasic inhibition (Nusser and Mody, 2002; Rossi et al., 2003).
