Kainate-induced seizures alter protein composition and N-methyl-D-aspartate receptor function of rat forebrain postsynaptic densities

The postsynaptic density is a highly dynamic structure, which is reorganize d in an activity-dependent manner. An animal model for temporal lobe epilep sy, i.e, kainate-induced limbic seizures in rats, was used to study changes in postsynaptic density composition after extensive synaptic activity. Six hours after kainate injection, the protein content of the postsynaptic den sity fractions from rats that developed strong seizures was increased three -fold compared to saline-treated controls. Immunoblot analysis revealed tha t the relative amounts of metabotropic glutamate receptor 1 alpha, N-ethyl- maleimide-sensitive fusion protein, protein kinases C, Fyn and TrkB, as wel l as the neuronal nitric oxide synthase, were significantly higher in seizu re-developing than in control rats. In contrast, the relative contents of t he kainate receptor KA2 subunit, beta -actin, alpha -adducin and the membra ne-associated guanylate kinase homolog SAP90/PSD-95 were decreased. The rel ative amounts of additional postsynaptic density proteins, including alpha -amino-3-hydroxy-5-methyl-4-isoxazolepropionate and N-methyl-D-aspartate re ceptor subunits, calcium/calmodulin-dependent kinase type II, casein kinase 2, tubulin, microtubule-associated protein 2B, the membrane-associated gua nylate kinase homolog SAP102, and proline-rich synapse associated protein 1 /cortactin binding protein 1/Shank2 remained essentially unchanged. To asse ss possible changes in postsynaptic performance, postsynaptic densities wer e isolated from control and epileptic rats, incorporated into giant liposom es and N-methyl-D-aspartate receptor currents were recorded. A significant reduction in the mean conductance was observed in patches containing postsy naptic densities from animals with high seizure activity. This was due to t he presence of reduced conductance levels in each membrane patch compared t o control postsynaptic density preparations. From these data, we suggest that intense synaptic activity associated with seizures modifies the composition of postsynaptic densities and has profoun d consequences on the function of the N-methyl-D-aspartate receptors presen t in them. This rearrangement may accompany impairment of synaptic plastici ty. (C) 2001 IBRO. Published by Elsevier Science Ltd. All rights reserved.