Research reportThe sedative but not the memory-blocking properties of ethanol are modulated by α5-subunit-containing γ-aminobutyric acid type A receptors

The precise mechanisms underlying the memory-blocking properties of ethanol are unknown, in part because ethanol targets a wide array of neurotransmitter receptors and transporters. The aim of this study was to determine whether the memory loss caused by ethanol is mediated, in part, by α5 subunit-containing γ-aminobutyric acid subtype A receptors. These receptors have been implicated in learning and memory processes and are targets for a variety of neurodepressive drugs. Also, since these receptors generate a tonic inhibitory current in hippocampal pyramidal neurons, we examined whether concentrations of ethanol that block memory in vivo increased the tonic current using whole-cell patch-clamp recordings in hippocampal neurons. Null mutant mice lacking the α5 subunit (Gabra5−/−) and wild-type mice were equally impaired in contextual fear conditioning by moderate (1 mg/kg) and high (1.5 mg/kg) doses of ethanol. The higher dose of ethanol also reduced auditory delay fear conditioning to the same extent in the two genotypes. Interestingly, wild-type mice were more sensitive than Gabra5−/− mice to the sedative effects of low (0.5 mg/kg) and moderate (1 mg/kg) doses of ethanol in the open-field task. Concentrations of ethanol that impaired memory performance in vivo did not increase the amplitude of the tonic current. Together, the results suggest that the α5-subunit containing γ-aminobutyric acid subtype A receptors are not direct targets for positive modulation by ethanol nor do they contribute to ethanol-induced memory loss. In contrast, these receptors may contribute to the sedative properties of ethanol.

Research highlights▶ Ethanol does not exert its memory-impairing effects through α5GABAA receptors. ▶ Behaviorally-relevant concentrations of ethanol do not enhance an α5GABAA receptor-mediated tonic inhibitory current in cultured hippocampal pyramidal neurons. ▶ The sedative properties of ethanol may be in part generated by ethanol's action on α5GABAA receptors.