Group 1 metabotropic glutamate receptor 5 is involved in synaptically-induced Ca(2+)-spikes and cell death in cultured rat hippocampal neurons

Group 1 metabotropic glutamate receptors (mGluRs) can positively affect postsynaptic neuronal excitability and epileptogenesis. The objective of the present study was to determine whether group 1 mGluRs might be involved in synaptically-induced intracellular free Ca(2+) concentration ([Ca(2+)](i)) spikes and neuronal cell death induced by 0.1 mM Mg(2+) and 10 µM glycine in cultured rat hippocampal neurons from embryonic day 17 fetal Sprague–Dawley rats using imaging methods for Ca(2+) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays for cell survival. Reduction of extracellular Mg(2+) concentration ([Mg(2+)](o)) to 0.1 mM induced repetitive [Ca(2+)](i) spikes within 30 sec at day 11.5. The mGluR5 antagonist 6-Methyl-2-(phenylethynyl) pyridine (MPEP) almost completely inhibited the [Ca(2+)](i) spikes, but the mGluR1 antagonist LY367385 did not. The group 1 mGluRs agonist, 3,5-dihydroxyphenylglycine (DHPG), significantly increased the [Ca(2+)](i) spikes. The phospholipase C inhibitor U73122 significantly inhibited the [Ca(2+)](i) spikes in the absence or presence of DHPG. The IP(3) receptor antagonist 2-aminoethoxydiphenyl borate or the ryanodine receptor antagonist 8-(diethylamino)octyl 3,4,5-trimethoxybenzoate also significantly inhibited the [Ca(2+)](i) spikes in the absence or presence of DHPG. The TRPC channel inhibitors SKF96365 and flufenamic acid significantly inhibited the [Ca(2+)](i) spikes in the absence or presence of DHPG. The mGluR5 antagonist MPEP significantly increased the neuronal cell survival, but mGluR1 antagonist LY367385 did not. These results suggest a possibility that mGluR5 is involved in synaptically-induced [Ca(2+)](i) spikes and neuronal cell death in cultured rat hippocampal neurons by releasing Ca(2+) from IP(3) and ryanodine-sensitive intracellular stores and activating TRPC channels.