Selective inhibition of forskolin-stimulated cyclic AMP formation in rat hippocampus by a novel mGluR agonist, 2 R,4 R-4-aminopyrrolidine-2,4-dicarboxylate

Abstract

Metabotropic glutamate receptors (mGluRs) are a heterogeneous family of G-protein coupled receptors that are linked to multiple second messengers in the rat hippocampus. The compound 1 S,3 R-1-aminocyclopentane-1,3-dicarboxylic acid (1 S,3 R-ACPD) has been widely used to activate this class of receptors and study their functions in situ. However, 1 S,3 R-ACPD acts on multiple mGluR subtypes to produce multiple alterations in second messengers. We report here that the aza-substituted analog of 1 S,3 R-ACPD, 2 R,4 R-4-aminopyrrolidine-2,4-dicarboxylate (2 R,4 R-APDC), is a highly selective agonist for negatively-coupled cAMP-linked mGluRs in the rat hippocampus, with similar potency in mGluR2 expressing cells. 1 S,3 R-ACPD decreases forskolin-stimulated cAMP formation, increases basal cAMP formation, and increases phosphoinositide hydrolysis in the rat hippocampus. However, 2 R,4 R-APDC inhibited forskolin-stimulated cAMP, but had none of the other activities of 1 S,3 R-APDC. Furthermore, 2 R,4 R-APDC had no measurable ionotropic glutamate receptor affinity in rat hippocampus, as indicated by lack of effects on basal and glutamate agonist-evoked [ 3H]norepinephrine release. 2 R,4 R-APDC also inhibited forskolin-stimulated cAMP formation in human mGluR2 expressing cells with about three-fold greater potency than 1 S,3 R-APDC, but unlike 1 S,3 R-APDC, showed no appreciable activation of phosphoinostide hydrolysis in human mGluP1α expressing cells. Thus, 2 R,4 R-APDC should be a useful pharmacological agent to explore the functions of mGluRs coupled to inhibition of adenylate cyclase.