Postsynaptic activity of metabotropic glutamate receptors in the piriform cortex

Effects of some glutamate receptor antagonists on signal propagation elicited by stimulation of association fibers in guinea pig piriform cortex slices were investigated using optical imaging. During simultaneous application of both NMDA and non-NMDA receptor antagonists (D-2-amino-5-phosphonopentanoic acid and 6-cyano-7-nitroquinoxaline-2,3-dione, respectively) the postsynaptic activity was largely suppressed, and a weak although distinct late propagation component was found to survive. This latter component was reversibly suppressed by application of low Ca(2+) solution or a group I/II specific metabotropic glutamate receptor (mGluR) antagonist (+)-alpha-methyl-4-carboxyphenylglycine. These results suggest that mGluRs mediate postsynaptic excitation, which would play a crucial role in activating the reverberating positive feedback circuit effectively.