Abstract: The metabotopic glutamate receptors (mGluRs) constitute a new family of excitatory amino acid receptors, which modulates the synaptic transmission by coupling to second messengers through G-proteins.[1] To date, mGluRs have been distinguished into three groups, based on sequence homology, signal transduction mechanisms and agents pharmacology. In particular, receptors of group III (mGluR4 and mGluR6-8) are characterized by their selective response to several phosphonic acid derivatives. Thus, they are selectively activated by L-2-amino-4- phosphonobutanoic acid (L-AP4, 1 in scheme 1) and competitively antagonized by the a-methylated derivatives of LAP4 (MAP4, 2) and 4-phosphonophenylglycine (MPPG, 3).[2]