MGLUR-II AGONIST INHIBITION OF LTP INDUCTION, AND MGLUR-II ANTAGONISTINHIBITION OF LTD INDUCTION, IN THE DENTATE GYRUS IN-VITRO

THE effects of the metabotropic glutamate receptor (mGluR) group II ag onist 1'R,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)glycine (DCG-IV) and the antagonist ,1S',2S'-2-methyl-2-(2'-carboxycyclopropyl)glycine (MCC G) on the induction of long-term potentiation (LTP) and long-term depr ession (LTD) of the field excitatory postsynaptic potential (epsp) in the dentate gyrus of the rat hippocampus were investigated in vitro. I n control media, high frequency stimulation (I-IFS) consisting of a se ries of trains of stimuli at 200 Hz induced LTP, and low frequency sti mulation (LFS) consisting of 900 stimuli at 1 Hz induced LTD. DCG-IV ( 50 nM) strongly inhibited the induction of LTP. The block of LTP induc tion was not caused by a frequency-dependent inhibition of the epsp du ring HFS, as the epsps evoked during HFS were not altered by DCG-IV. M CCG (500 mu M) did not inhibit the induction of LTP, but did prevent t he block of LTP by DCG-IV. MCCG (500 mu M) strongly inhibited the indu ction of LTD. DCG-IV (50 nM) did not inhibit LTD induction.