Functional downregulation of GluR2 in piriform cortex of kindled animals

We have previously shown kindling-induced downregulation of the AMPA recept or GluR2 subunit in piriform cortex, as measured by Western blotting. In th e present studies, we performed whole-cell patch clamp analysis of AMPA rec eptor-mediated currents from kindled and control animals to determine if th e downregulation observed previously had any functional significance. These experiments were done in the absence and presence of N-hydroxyphenylpropan oyl spermine (HPPS), a polyamine that blocks currents through AMPA receptor s lacking GluR2. We report that AMPA receptor-mediated currents recorded fr om piriform cortex layer II pyramidal cells in slices from animals kindled to 10 fully generalized seizures were blocked by HPPS. In contrast, applica tion of HPPS had no effect on current amplitude in control animals, or in a nimals that had not been fully kindled. Western blotting revealed that decr eases in GluR2 were seen in animals that had experienced at least one fully generalized seizure, but were not observed at earlier stages of kindling d evelopment. The increased polyamine sensitivity of AMPA receptor-mediated c urrents in kindled animals is consistent with the hypothesis that kindling induces formation of AMPA receptors that lack GluR2 in piriform cortex pyra midal cells. It has been demonstrated that polyamine sensitivity is directl y correlated with the calcium permeability of the AMPA receptor, suggesting that kindling results in the formation of AMPA receptors that are calcium- permeable. Increases in intracellular calcium through these receptors could act as a second messenger and play a role in the initiation of long-term c hanges that contribute to the pathogenesis of kindling-induced epilepsy. (C ) 2000 Wiley-Liss, Inc.