Differential alteration of NMDA receptor subunits in the gerbil dentate gyrus and subiculum following seizure

In the present study, a chronological and comparative analysis of the immunoreactivities of N-methyl-D-aspartate (NMDA) receptor subunits in hippocampus of both seizure resistant (SR) and seizure sensitive (SS) gerbils was made in order to clarify the temporal and spatial alterations of NMDA receptor subunit expressions in the hippocampus complex. The changes in NMDA receptor immunoreactivity in the hippocampi of SS gerbils were restricted to both the dentate gyrus and the subiculum. At 30 min postictal, a decline in NMDA receptor subunit 1 (NR1) immunoreactivity in the suprablade of dentate gyrus was observed. This is in contrast to the enhancement of its immunodensity in the infrablade. At 3 h postictal the NR1 immunoreactivity in the infrablade also declined significantly. At 12 h postictal, its immunoreactivity in the hilar neurons was reduced. The NMDA receptor subunit 2A/B (NR2A/B) immunoreactivity did not alter until 12 h following seizure-onset, when it was slightly decreased in the granule cells and hilar neurons. In the subiculum, NR1 immunoreactivity was significantly decreased, and was almost undetectable in this region until 12 h postictal; in contrast the NR2A/B immunoreactivity in this region increased significantly in this time point. These results suggest that the altering NMDA receptor expression in both the dentate gyrus and subiculum may affect tissue excitability and have an important role in regulating seizure activity in SS gerbils.