CPPG ((RS)-CPPG) potently reversed both L-AP4 (IC50: 2.2 nM)- and L-CCG-I (IC50: 46.2 nM) -mediated inhibition of forskolin-stimulated cyclic AMP accumulation in adult rat cortical slices. CPPG has weak effects at the group I mGlu receptors in both the neonatal rat cortex and cultured cerebellar granule cells.