(S)-MCPG is the active isomer of (RS)-MCPG (Cat. No. HY-100371), non-selective group I/group II metabotropic glutamate receptor antagonist. In vivo: (S)-MCPG (20.8 μg) injected intraventricularly (i.c.v.) before testing impaired the performance of rats in the spatial version of the Morris water maze, but 1/10 of this dose did not. Memory retention, evaluated 24 hr post-training, is also affected by the high dose of MCPG.