Class I metabotropic glutamate receptor agonists do not facilitate the induction of long-term potentiation in the dentate gyrus of the rat in vitro

The possibility that activation of class I (phospholipase C-coupled) metabotropic glutamate receptors (MGluRs) can facilitate the induction of long-term potentiation (LTP) was investigated in the dentate gyrus of rat hippocampal slices. In the presence of picrotoxin, a weak tetanus led to a short-term potentiation (STP) lasting 10-15 min. Application of the class I mGluR agonists trans-azetidine-2,4-dicarboxylic acid (tADA, 100 mu M) or 3,5-dihydroxyphenylglycine (DHPG, 100 mu M) for 15 or 30 min before the weak tetanus did not affect baseline synaptic transmission or the magnitude of the subsequent potentiation. DHPG (70 mu M) did, however, reduce accommodation of neuronal firing in response to depolarizing current injection. These results suggest that at the medial perforant path-granule cell synapse, class I mGluR activation by exogenous agonist application does not facilitate the induction of LTP.