Suppression of neuronal network excitability and seizure-like events by 2-methyl-4-oxo-3H-quinazoline-3-acetyl piperidine in juvenile rat hippocampus: involvement of a metabotropic glutamate receptor.

We present data on the antiepileptic potency of 2-methyl-4-oxo-3H-quinazoline-3-acetyl piperidine (Q5) in juvenile (P9-13) rat hippocampal slices and in particular Q5's action mechanism and target. Q5 (200-500 microM), but not alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)/Kainate receptor antagonists blocked low-[Mg2+]-induced seizure-like events (SLE) in the CA3 region. Q5 (100 microM) decreased Glu-induced [35S]guanosine 5'-O-(3-thiotriphosphate) binding enhancement in brain homogenates, without interaction with ionotropic Glu receptor sites and Glu transport. In voltage-clamped CA3 pyramidal cells, Q5 (500 microM) depressed activities of spontaneous excitatory and inhibitory postsynaptic currents without affecting miniature inhibitory currents. Metabotropic Glu receptor (mGluR) subtype antagonists affected network excitability dissimilarly. Intracellular Ca2+ ion transients induced by the mGluR agonist (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD) were suppressed by Q5. Agreeing predictions obtained by modelling Q5 binding to different experimental conformations of mGlu1, Q5 was bound partially to an mGluR binding site in the presence of 1mM ACPD. Findings suggest the apparent involvement of a novel phenotype of action or a new mGluR subtype in the specific suppression of epileptiform activity by Q5 through the depression of network excitability.