Rationale: Although convergent evidence exists for a role of glutamate in the regulation of anxiety, the involvement of specific glutamate receptor subtypes has yet to be defined.
Objective: To evaluate the potential for blockade of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)/kainate receptors to produce anxioltyic-like effects with the AMPA/GLU(K5) (kainate) antagonist (3S,4aR,6R,8aR)-6-[2-(1(2)H-tetrazole-5yl)ethyl]decahydroisoquinoline-3carboxylic acid (LY293558)
Materials and methods: Punished responding of rats was used to determine the efficacy of LY293558. Other in vivo and in vitro studies further characterized the specificity of LY293558 for AMPA/kainate receptors.
Results: LY293558 had a rank order of potency of GLU(K5) > or = GLU(K5/6) approximately GLU(A2i) approximately GLU(K2/5) approximately GLU(A1i) approximately GLU(A2o) approximately GLU(A3i) approximately GLU(A1o) > or = GLU(A3o) > or = GLU(A4i) approximately GLU(A4o) and >100 microM affinity for rat cortical GABA(A) receptors. Comparison of the blockade of AMPA- vs N-methyl-D-aspartate (NMDA)-induced inward currents demonstrated that LY293558 was five-fold more potent as an antagonist at AMPA vs NMDA receptors in vitro. In keeping with the low affinity of LY293558 for NMDA receptors, LY293558 was not effective in preventing NMDA-induced seizures in mice. LY293558 increased punished responding, a preclinical predictor of anxiolytic efficacy, at a dose that decreased unpunished responding (10 mg/kg, i.p.). Chlordiazepoxide produced comparable increases in both punished and unpunished responding. The NMDA antagonist dizocilpine [(+)-MK-801] also increased both punished and unpunished responding.
Conclusions: These data along with those in the literature suggest that AMPA and/or kainate receptor blockade may be an important component to producing anxiolytic-like effects and may therefore be a target for compounds with efficacy in the therapeutic treatment of anxiety disorders.