A Pharmacogenetic 'Restriction-of-Function' Approach Reveals Evidence for Anxiolytic-Like Actions Mediated by α5-Containing GABAA Receptors in Mice.

Benzodiazepines have been widely used for their anxiolytic actions. However, the contribution of GABAA receptor subtypes to anxiolysis is still controversial. Studies with mutant mice harboring diazepam-insensitive α-subunits α1, α2, α3, or α5 have revealed that α2-containing GABAA receptors (α2-GABAARs) are required for diazepam-induced anxiolysis, with no evidence for an involvement of any other α-subunit, whereas TP003, described as a selective modulator of α3-containing GABAA receptors, was shown to be anxiolytic. Here, we describe a novel, systematic approach to evaluate the role of positive allosteric modulation of each of the four diazepam-sensitive α-subtypes in anxiety-related behavioral paradigms. By combining H to R point mutations in three out of the four diazepam-sensitive α-subunits in mice with a 129X1/SvJ background, diazepam becomes a subtype-specific modulator of the remaining non-mutated α-subtype. Modulation of α5-GABAARs, but not of α2-GABAARs, increased the time in the light side of the light-dark box as well as open-arm exploration in the elevated plus maze. In contrast, modulation of α3-GABAARs decreased open-arm exploration, whereas modulation of α2-GABAARs increased time in the center in the open-field test. Modulation of any single α-subtype had no effect on stress-induced hyperthermia. Our results provide evidence that modulation of α5-GABAARs elicits anxiolytic-like actions, whereas our data do not provide evidence for an anxiolytic-like action of α3-GABAARs. Thus, α5-GABAARs may be suitable targets for novel anxiolytic drugs.