Antagonism of the presumed presynaptic action of L-AP4 on GABAergic transmission in the ventrobasal thalamus by the novel mGluR antagonist MPPG.

The metabotropic glutamate receptor (mGluR) agonists CCG-I and L-AP4, acting at Group II and Group III mGluRs respectively, can reduce GABAergic synaptic inhibition on single neurones in the rat thalamus in vivo via a presumed presynaptic mechanism. The actions of L-AP4 were antagonized by (+/-)-alpha-methyl-4-phosphonophenylglycine (MPPG), whereas CCG-I was significantly less affected. Thus MPPG may be a useful tool for detecting physiological roles for Group III mGluRs.