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 Ba ´lint Laszto ´czi * , Zsuzsa Emri, E ´ va Sza ´rics, La ´szlo ´ He ´ja, A ´ gnes Simon, Lajos Nyikos, Julianna Kardos Department of Neurochemistry, Institute of Biomolecular Chemistry, Chemical Research Center, Hungarian Academy of Sciences, 1025 Pusztaszeri u ´t 59-67, Budapest, Hungary Received 25 October 2005; received in revised form 19 December 2005; accepted 20 December 2005 Available online 21 February 2006 Abstract 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 mM), but not a-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)/Kainate receptor antagonists blocked low-[Mg 2+ ]-induced seizure-like events (SLE) in the CA3 region. Q5 (100 mM) decreased Glu- induced [ 35 S]guanosine 5 0 -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 mM) 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 Ca 2+ 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 1 mM 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. # 2006 Elsevier Ltd. All rights reserved. Keywords: 2-Methyl-4-oxo-3H-quinazoline-3-acetyl piperidine; Seizure-like events; Network excitability; Cytosolic Ca 2+ ion transients; Glutamate binding targets; Metabotropic glutamate receptors 1. Introduction Compounds characterised by the substituted 4-oxo-3H- quinazoline skeleton had previously been shown to inhibit metrazole-induced convulsions in rats (Misra et al., 1982) suggesting that 2-methyl-4-oxo-3H-quinazoline-3-acetyl piperidine (Q5; Sza ´rics et al., 2001) may also have antic- onvulsant properties. Indeed, Q5 (50 mM) specifically blocked low-[Mg 2+ ]-induced seizure-like events (SLEs) in the CA3 region of hippocampal slices from adolescent (P28-34) rats without affecting the interictal activity (Laszto ´ czi et al., 2002). By contrast, the antagonist of a-amino-3-hydroxy-5- methylisoxazole-4-propionic acid (AMPA)/Kainate receptors, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) blocked both, SLEs as well as the interictal activity (Laszto ´czi et al., 2002). The specific seizure-inhibitory property of Q5 challenged us to delineate the mechanism and the target of its action, which may provide a clue for the design of pathomechanism-selective antiepileptic drugs (AEDs). Ionotropic Glu receptors (iGluR) of AMPA-, Kainate- and N-methyl-D-aspartate (NMDA)-type (Dingledine et al., 1999) as well as groups I–III metabotropic Glu receptors (mGluR; Pin and Acher, 2002) and excitatory amino acid transporters (EAATs) are known to be involved in the generation of epileptiform activity (Zhang et al., 1994; Meldrum et al., 1999; Doherty and Dingledine, 2002; Demarque et al., 2004). Most probably due to major psychological side-effects, toxicity and poor blood–brain barrier penetration, however, there is no AED targeting the Gluergic system on the market at present (Lo ¨scher, 2002; Moldrich et al., 2003). Therefore, any new molecules acting www.elsevier.com/locate/neuint Neurochemistry International 49 (2006) 41–54 * Corresponding author. Tel.: +36 1 3257530x263; fax: +36 1 3257554. E-mail address: laszto@chemres.hu (B. Laszto ´czi). 0197-0186/$ – see front matter # 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.neuint.2005.12.017