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Non-selective benzodiazepines, such as diazepam, interact with equivalent affinity and agonist efficacy at GABAA receptors containing either an α1, α2, α3 or α5 subunit. However, which of these particular subtypes are responsible for the anticonvulsant effects of diazepam remains uncertain. In the present study, we examined the ability of diazepam to reduce pentylenetetrazole (PTZ)-induced and maximal electroshock (MES)-induced seizures in mice containing point mutations in single (α1H101R, α2H101R or α5H105R) or multiple (α125H→R) α subunits that render the resulting GABAA receptors diazepam-insensitive. Furthermore, the anticonvulsant properties of diazepam, the α1- and α3-selective compounds zolpidem and TP003, respectively, and the α2/α3 preferring compound TP13 were studied against PTZ-induced seizures. In the transgenic mice, no single subtype was responsible for the anticonvulsant effects of diazepam in either the PTZ or MES assay and neither the α3 nor α5 subtypes appeared to confer anticonvulsant activity. Moreover, whereas the α1 and α2 subtypes played a modest role with respect to the PTZ assay, they had a negligible role in the MES assay. With respect to subtype-selective compounds, zolpidem and TP003 had much reduced anticonvulsant efficacy relative to diazepam in both the PTZ and MES assays whereas TP13 had high anticonvulsant efficacy in the PTZ but not the MES assay. Taken together, these data not only indicate a role for α2-containing GABAA receptors in mediating PTZ and MES anticonvulsant activity but also suggest that efficacy at more than one subtype is required and that these subtypes act synergistically. [ABSTRACT FROM AUTHOR]

The GABAA receptor subtypes responsible for the anxiolytic effects of nonselective benzodiazepines (BZs) such as chlordiazepoxide (CDP) and diazepam remain controversial. Hence, molecular genetic data suggest that α2- rather than α3-containing GABAA receptors are responsible for the anxiolytic effects of diazepam, whereas the anxiogenic effects of an α3-selective inverse agonist suggest that an agonist selective for this subtype should be anxiolytic. We have extended this latter pharmacological approach to identify a compound, 4,2′-difluoro-5′-[8-fluoro-7-(1-hydroxy-1-methylethyl)imidazo[1,2-á]pyridin-3-yl]biphenyl-2-carbonitrile (TP003), that is an α3 subtype selective agonist that produced a robust anxiolytic-like effect in both rodent and non-human primate behavioral models of anxiety. Moreover, in mice containing a point mutation that renders α2-containing receptors BZ insensitive (α2H101R mice), TP003 as well as the nonselective agonist CDP retained efficacy in a stress-induced hyperthermia model. Together, these data show that potentiation of α3-containing GABAA receptors is sufficient to produce the anxiolytic effects of BZs and that α2 potentiation may not be necessary. [ABSTRACT FROM AUTHOR]