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The Journal of Neuroscience, March 18, 2009, 29(11):3497-3507; doi:10.1523/JNEUROSCI.5447-08.2009

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Neurobiology of Disease
Cellular Plasticity for Group I mGluR-Mediated Epileptogenesis

Riccardo Bianchi, Shih-Chieh Chuang, Wangfa Zhao, Steven R. Young, and Robert K. S. Wong

The Robert F. Furchgott Center for Neural and Behavioral Science and Department of Physiology and Pharmacology, State University of New York Downstate Medical Center, Brooklyn, New York 11203

Correspondence should be addressed to Riccardo Bianchi, Department of Physiology and Pharmacology, Box 29, State University of New York Downstate Medical Center, 450 Clarkson Avenue, Brooklyn, NY 11203. Email: rbianchi{at}downstate.edu

Stimulation of group I metabotropic glutamate receptors (mGluRs) by the agonist (S)-dihydroxyphenylglycine in the hippocampus transforms normal neuronal activity into prolonged epileptiform discharges. The conversion is long lasting in that epileptiform discharges persist after washout of the inducing agonist and serves as a model of epileptogenesis. The group I mGluR model of epileptogenesis took on special significance because epilepsy associated with fragile X syndrome (FXS) may be caused by excessive group I mGluR signaling. At present, the plasticity mechanism underlying the group I mGluR-mediated epileptogenesis is unknown. I_mGluR(V), a voltage-gated cationic current activated by group I mGluR agonists in CA3 pyramidal cells in the hippocampus, is a possible candidate. I_mGluR(V) activation is associated with group I mGluR agonist-elicited epileptiform discharges. For I_mGluR(V) to play a role in epileptogenesis, long-term activation of the current must occur after group I mGluR agonist exposure or synaptic stimulation. We observed that I_mGluR(V), once induced by group I mGluR agonist stimulation in CA3 pyramidal cells, remained undiminished for hours after agonist washout. In slices prepared from FXS model mice, repeated stimulation of recurrent CA3 pyramidal cell synapses, effective in eliciting mGluR-mediated epileptiform discharges, also induced long-lasting I_mGluR(V) in CA3 pyramidal cells. Similar to group I mGluR-mediated prolonged epileptiform discharges, persistent I_mGluR(V) was no longer observed in preparations pretreated with inhibitors of tyrosine kinase, of extracellular signal-regulated kinase 1/2, or of mRNA protein synthesis. The results indicate that I_mGluR(V) is an intrinsic plasticity mechanism associated with group I mGluR-mediated epileptogenesis.

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Received Nov. 11, 2008; revised Feb. 10, 2009; accepted Feb. 15, 2009.

Correspondence should be addressed to Riccardo Bianchi, Department of Physiology and Pharmacology, Box 29, State University of New York Downstate Medical Center, 450 Clarkson Avenue, Brooklyn, NY 11203. Email: rbianchi{at}downstate.edu

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