Chronic pre-explant blockade of the NMDA receptor affects survival of cerebellar granule cells explanted in vitro

Rat pups were treated with the competitive NMDA antagonist CGP 39551 with daily injections on postnatal days 1 to 8. Cultures of cerebellar granule cells were prepared from these pups as well as from control pups of the same age and body weight. Granule neurons explanted from CGP 39551-treated pups showed a decreased survival, both at short (2 days) or longer (8 days) time in vitro, irrespective of trophic (high K+) or non-trophic (low K+) culture conditions. Granule cells from control or treated animals underwent apoptotic death when shifted from high to low K+ after maturation in vitro and were rescued by lithium (5 mM). Under the same experimental conditions, the block of protein synthesis through cycloheximide only partially protected from apoptotic death granule neurons from control rats, whereas it was totally effective on cultures derived from CGP 39551-treated animals. This suggests that a different balance between apoptotic/necrotic cell death may be the result of the same experimental conditions in the two types of cultures. Finally, the acquisition of excitotoxic sensitivity to glutamate and the protection given by MK-801 were the same in both types of cultures. The present results demonstrate that the previous block of the NMDA receptor negatively affects the subsequent survival of granule cells once they are explanted in vitro, whereas some features related to the maturation of these neurons in vitro are not impaired.