Low-dose alcohol actions on α4β3δ GABAAreceptors are reversed by the behavioral alcohol antagonist Ro15-4513

Publisher Website
Google Scholar
Abstract
Although it is now more than two decades since it was first reported that the imidazobenzodiazepine Ro15-4513 reverses behavioral alcohol effects, the molecular target(s) of Ro15-4513 and the mechanism of alcohol antagonism remain elusive. Here, we show that Ro15-4513 blocks the alcohol enhancement on recombinant “extrasynaptic” α4/6β3δ GABAAreceptors at doses that do not reduce the GABA-induced Cl−current. At low ethanol concentrations (≤30 mM), the Ro15-4513 antagonism is complete. However, at higher ethanol concentrations (≥100 mM), there is a Ro15-4513-insensitive ethanol enhancement that is abolished in receptors containing a point mutation in the second transmembrane region of the β3 subunit (β3N265M). Therefore, α4/6β3δ GABA receptors have two distinct alcohol modulation sites: (i) a low-dose ethanol site present in α4/6β3δ receptors that is antagonized by the behavioral alcohol antagonist Ro15-4513 and (ii) a site activated at high (anesthetic) alcohol doses, defined by mutations in membrane-spanning regions. Receptors composed of α4β3N265Mδ subunits that lack the high-dose alcohol site show a saturable ethanol dose-response curve with a half-maximal enhancement at 16 mM, close to the legal blood alcohol driving limit in most U.S. states (17.4 mM). Like in behavioral experiments, the alcohol antagonist effect of Ro15-4513 on recombinant α4β3δ receptors is blocked by flumazenil and β-carboline-ethyl ester (β-CCE). Our findings suggest that ethanol/Ro15-4513-sensitive GABAAreceptors are important mediators of behavioral alcohol effects.