Rat Hippocampal Kindling Induces Changes in the Glutamate Receptor mRNA Expression Patterns in Dentate Granule Neurons

The expression level of the mRNAs encoding the Flip and Flop versions of the AMPA-selective glutamate receptor subunits A, B, C and D was studied using in situ hybridization in the hippocampus of rats kindled by Schaffer collateral/commissural fibre stimulation. The expression levels of the Flip variant of GluR-A, B and C mRNAs were bilaterally enhanced in the dentate granule neurons of fully kindled animals 24 h after the last seizure. These changes were already observed after the sixth kindling stimulation (preconvulsive-stage), but not after a single afterdischarge. Four weeks after the last seizure, when the animals were still hypersensitive to kindling stimulations, only GluR-A Flip expression was enhanced. These results suggest that kindling epileptogenesis is accompanied by an increased number and enhanced sensitivity of the expressed AMPA type glutamate receptors in the fascia dentata, leading to an enhanced excitatory synaptic transmission which may contribute to the process of kindling epileptogenesis.