(1S,2S,5R,6S)-2-Aminobicyclo[3.1.0]hexane-2,6-dicarboxylic acid (LY354740) is a potent and selective agonist for group II metabotropic glutamate (mGlu2 and mGlu3) receptors, with anxiolytic-like activity in animal and human models, and efficacy in anxiety patients. However, the lack of mGlu2 or mGlu3 receptor specific agonists has prevented in vivo characterization of individual functions of these two receptors in mediating the anxiolytic-like effects of LY354740.To utilize mGlu2 receptor and mGlu3 receptor knockout animals and the mGlu2/3 selective antagonist (2S,1'S,2'S)-2-(9-xanthylmethyl)-2-(2'-carboxycyclopropyl)glycine (LY341495) to further investigate the roles of mGlu2 and mGlu3 receptors in mediating the anxiolytic-like actions of LY354740 in a mouse model of anxiety [elevated plus maze (EPM) test].To confirm that mGlu2/3 receptors are responsible for anxiolytic-like activity in the EPM under these test conditions, mice were pretreated with LY341495 at 30 min prior to s.c. administered LY354740. Subsequently, saline vehicle or LY354740 was administered (s.c.) 30 min before the EPM testing in wild-type, mGlu2 receptor knockout, and mGlu3 receptor knockout mice.LY354740 reduced in a dose-dependent manner anxiety-related behavior on the EPM in wild-type mice with a maximally effective dose of 10--20 mg/kg s.c. Pretreatment with LY341495 potently prevented the anxiolytic-like effects of LY354740 (20 mg/kg, s.c.) in mice. Although the mGlu2 receptor knockout and mGlu3 receptor knockout mice were grossly normal, the anxiolytic-like activity of LY354740 (20 mg/kg, s.c.) was not evident in either mGlu2 or mGlu3 receptor knockout mice, when compared to their wild-type controls.The activation of both mGlu2 and mGlu3 receptors by LY354740 appears to be required for anxiolytic-like activity in the EPM test in mice. These studies serve as a foundation for additional studies on underlying circuits, brain structures, and receptor subtypes involved in the anxiolytic-like actions of mGlu receptor active agents, and the design of future drugs for anxiety disorders in humans.