DIFFERENTIAL REGULATION OF SYNAPTIC INPUTS TO DENTATE HILAR BORDER INTERNEURONS BY METABOTROPIC GLUTAMATE RECEPTORS

Regulation of synaptic transmission by metabotropic glutamate receptor s (mGluRs) was examined at two excitatory inputs to interneurons with cell bodies at the granule cell-hilus border in hippocampal slices tak en from neonatal rats. Subgroup-selective mGluR agonists altered the r eliability, or probability of transmitter release, of evoked minimal e xcitatory synaptic inputs and decreased the amplitudes of excitatory p ostsynaptic currents (EPSCs) evoked with conventional stimulation. The group II-selective agonist, (2S,1R',2R',3R')-2-(2,3-dicarboxylcyclopr opyl) glycine (DCG-IV; 1 mu M), reversibly depressed the reliability o f EPSCs evoked by stimulation of the dentate granule cell layer. Howev er, DCG-IV had no significant effect on EPSCs evoked by CA3 stimulatio n in the majority (82%) of hilar border interneurons. Both the group I II-selective agonist, L-(+) -2-amino-4-phosphonobutyric acid (L-AP4; 3 mu M), and the group I-selective agonist, (RS)3,5-dihydroxyphenylglyc ine (DHPG; 20 mu M) reversibly depressed synaptic input to interneuron s from both CA3 and the granule cell layer. We conclude that multiple pharmacologically distinct mGluRs presynaptically regulate synaptic tr ansmission at two excitatory inputs to hilar border interneurons. Furt her, the degree of mGluR-meditated depression of excitatory drive is g reater at synapses from dentate granule cells onto interneurons than a t synapses from CA3 pyramidal cells.