The δ subunit-containing GABAA receptors, partnered with the α4, or α6 subunits, and especially with β3, are more sensitive than γ2-containing receptors to general anesthetics, neurosteroids, GABA analogs like THIP (Gaboxadol) (Wohlfarth et al., 2002; Brown et al., 2002; Chandra et al., 2006), as well as taurine (Jia et al., 2008) and ethanol (Wallner et al., 2003; Hanchar et al., 2005).The α4β2δ and α4β3δ receptors differ in sensitivity to modulators when recombinantly expressed in cells and both clearly occur naturally, because some brain areas express α4 and δ but not β2, or β3, subunits and display a pharmacology that distinguishes between these receptors. Thus, thalamic relay nuclei mainly express the β2 subunit and the moderately ethanol-sensitive α4β2δ receptor definitely mediates the tonic current (Chandra et al., 2006). Dentate granule cells express high levels of highly ethanol-sensitive, presumably α4β3δ isoforms (Liang et al., 2006), but additionally express the etomidate-sensitive α4β2δ isoforms (Herd et al., 2008). Partnering of either β2, or β3, with both the α4δ and α6δ subunits thus appears highly likely, even conclusive. Therefore, we added α4β2δ and α4β3δ, α6β2δ and α6β3δ subtypes to the list of “receptors identified”, replacing the generic α4βδδand α6βδ.
