Activation of Metabotropic Glutamate Receptors in the Hippocampus Increases Cyclic AMP Accumulation

The selective metabotropic glutamate receptor agonist trans-1-aminocyclopentane-1,3-dicarboxylic acid (trans-ACPD) stimulates phosphoinositide hydrolysis and elicits several physiological responses in rat hippocampal slices. However, recent studies suggest that the physiological effects of trans-ACPD in the hippocampus are mediated by activation of a receptor that is distinct from the phosphoinositide hydrolysis-linked receptor. Previous experiments indicate that cyclic AMP mimics many of the physiological effects of trans-ACPD in hippocampal slices. Furthermore, recent cloning and biochemistry experiments indicate that multiple metabotropic glutamate receptor subtypes exist, some of which are coupled to yet unidentified effector systems. Thus, we performed a series of experiments to test the hypothesis that ACPD increases cyclic AMP levels in hippocampal slices. We report that 1S,3R- and 1S,3S-ACPD (but not 1R,3S-ACPD) induce a concentration-dependent increase in cyclic AMP accumulation in hippocampal slices. This effect was blocked by the metabotropic glutamate receptor antagonist L-2-amino-3-phosphonoproprionic acid but not by selective antagonists of ionotropic glutamate receptors. Furthermore, our results suggest that 1S,3R-ACPD-stimulated increases in cyclic AMP accumulation are not secondary to increases in cell firing or to activation of phosphoinositide hydrolysis.