Seizure-related changes in the glutamate R2 and R5 receptor genes expression in the rat hippocampal formation.

The expression of mRNA coding for AMPA selective glutamate (Glu) R2 receptor and kainate selective GluR5 receptor was studied in the rat hippocampal formation in two animal models of limbic seizures evoked by systemic administration of pilocarpine (400 mg/kg i.p.) or kainate (15 mg/kg i.p.). As shown by an in situ hybridization study, pilocarpine decreased the GluR2 flip mRNA level in CA1 and CA3 areas of the hippocampus after 3h and kainate after 24h, e.g. at the time preceding neuronal degeneration. No changes in the GluR2 flop or GluR5 mRNA level were found in those regions. In the dentate gyrus, resistant to neurodegeneration, pilocarpine and kainate differentially affected the expression of GluR2 and GluR5 mRNAs. After 72h pilocarpine, but not kainate, increased the GluR2 flop mRNA level and decreased the flip one, which suggests attenuation of the GluR2 sensitivity. On the other hand, kainate, elevated the GluR2 flip and GluR5 mRNA level in the dentate gyrus after 72h. All in all the above data suggest that changes in the GluR2 gene expression may play some role in the neuronal damage to vulnerable areas (CA1, CA3). However, differences in the kainate-and pilocarpine-induced changes in the dentate gyrus at the late time points indicate that alterations in the stoichiometry of GluR2 forms of GluR5 gene expression in this brain region are not a common causal factor responsible for delayed neuronal hyperexcitability.