Metabotropic glutamate 7 receptor agonist AMN082 inhibits glutamate release in rat cerebral cortex nerve terminal

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AMN082 is a selective metabotropic glutamate mGlu7 receptor agonist reported to exhibit antidepressant activity. Considering that excessive glutamate release is involved in the pathogenesis of depression, the effect of N,N′-dibenzyhydryl-ethane-1,2-diamine dihydrochloride (AMN082) on glutamate release in rat cerebrocortical nerve terminals and the possible underlying mechanism were investigated. In this study, we observed here that AMN082 inhibited 4-aminopyridine-evoked glutamate release and this phenomenon was blocked by the metabotropic glutamate mGlu7 receptor antagonist MMPIP. Moreover, western blot analysis and immunocytochemistry confirmed the presence of presynaptic metabotropic glutamate mGlu7 receptor proteins. The effect of AMN082 on the 4-aminopyridine-evoked release of glutamate was prevented by chelating the extracellular Ca2+ ions and the vesicular transporter inhibitor; however, the effect of AMN082 was unaffected by the glutamate transporter inhibitor. AMN082 reduced the elevation of 4-aminopyridine-evoked intrasynaptosomal Ca2+ concentration, but did not alter the synaptosomal membrane potential. In the presence of the Cav2.2 (N-type) and Cav2.1 (P/Q-type) channel blocker, the adenylate cyclase inhibitor, and the protein kinase A inhibitor, the action of AMN082 on the 4-aminopyridine-evoked glutamate release was markedly reduced. These results suggest that the activation of the metabotropic glutamate mGlu7 receptors by AMN082 reduces adenylate cyclase/protein kinase A activation, which subsequently reduces the entry of Ca2+ through voltage-dependent Ca2+ channels and decreases evoked glutamate release. Additionally, fluoxetine, a clinically effective antidepressant, completely occluded the inhibitory effect of AMN082 on glutamate release, thus indicating the existence of a common intracellular mechanism for these two compounds to inhibit glutamate release from the cerebrocortical nerve terminals.

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