235 Role of metabotropic glutamate receptors on epileptiform activities in the rat cortical slice

Abstract

Since group II metabotropic glutamate (mGlu) receptors are a potential target for the amelioration of neuronal injury, we evaluated the ability of group II mGlu receptor agonists to attenuate toxicity induced by various insults in cortical, striatal and cerebellar granular (CGCs) pure neuronal cultures. The three cultures, when maintained under serum-free, anti-oxidant rich conditions for up to 13 days in vitro (div) were shown by immunocytochemistry to contain a maximum of 2–7% glia. At 6, 9 and 13 div a graded pattern of injury to cortical and striatal cultures was achieved with either hydrogen peroxide (60–110 μM), staurosporine (1 μM), N-methyl-D-aspartate (NMDA, 70 μM), α-amino-3-hydroxy-methylisoxazole-4-propionate (AMPA, 100 μM) or kainate (100 μM) over either 4, 24 or 48 h. CGCs were similarly exposed to low K+ (5.4 mM KCl). Cell viability was examined via phase-contrast microscopy and assessed by a 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide assay. Treatment with group II mGlu receptor agonists (1–300 μM), 2R,4R-4-aminopyrrolidine-2,4-dicarboxylate ((2R,4R)-APDC), (2S,1′S,2′S)-2-(carboxycyclopropyl)glycine (L-CCG-I), (2S,2′R,3′R)-2-(2′,3′-dicarboxycyclopropyl)glycine (DCG-IV) and N-acetylaspartylglutamate (NAAG) failed to attenuate the toxicity. Pretreatment of cultures with the agonists and treatment following acute insult also failed to attenuate toxicity. Further investigations demonstrated the presence of second messenger activation whereby (2R,4R)-APDC reduced forskolin-stimulated production of cAMP in each culture. Thus, despite receptor coupling to intracellular signaling cascades, and regardless of culture development, agonist concentration, extent and mode of injury, group II mGlu receptor agonists were unable to protect against injury induced in cortical, striatal and cerebellar granular pure neuronal cultures. This result is in contrast to mixed cultures of neurones and glia and implies an important role for glia in the neuroprotective effects of group II mGlu receptor agonists.