CPPG ((RS)-CPPG) is a potent group II/III mGlu receptor antagonist. CPPG exhibits some selectivity (approximately 20 fold) for group III (IC₅₀=2.2 nM) over group II (IC₅₀=46.2 nM) mGlu receptors in the rat cerebral cortex. CPPG has weak effects at group I mGlu receptors^[1]. In Vitro: 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 is a potent antagonist against group II/III mGlu receptors in the adult rat cortex and shows moderate selectivity for group III mGlu receptors. Conversely, CPPG has weak effects at group I mGlu receptors in both the neonatal rat cortex and cultured cerebellar granule cells^[1].