Crush injury induces NMDA-receptor-dependent delayed nerve cell death in rat entorhinal-hippocampal slice cultures

The aim of the present study was to develop an in vitro model that produces an injury-induced delayed nerve cell death. We used entorhinal-hippocampal slices from 12-day-old rats, which were cultured for 14 days before experiments prior to a crush injury in the middle layers of the entorhinal cortex. Crush injury increased specific propidium iodide (PI) fluorescence at the site of primary injury at day 1. Specific PI fluorescence decreased over the following days, with a slower decrease taking place at days 4-7. At days 4-7, PI fluorescence increased in CA1 and CA3. Treatment with 30 microM MK-801 for 2 h at the time of crush injury prevented the increase in PI fluorescence at days 4-7 at the site of injury, in CA1, and in CA3. Crush injury induced TUNEL-positive cells at the site of injury at days 1 and 5. MK-801 markedly reduced the number of TUNEL-positive cells observed at day 5, but had no effect on the number of TUNEL-positive cells at day 1. The present data indicate that crush injury may induce two types of secondary cell death. The first, early, type of cell death is induced quickly and is maximal at day 1, after which the dead cells are gradually removed. The second, delayed, type of cell death appears at day 4. NMDA receptor antagonism prevents the induction of the delayed cell death but has no effect on the early cell death.