NMDA receptors mediate anoxia/aglycemia-induced release of eicosanoids in immature rat hippocampal slices: utility of an in vitro "ischemic" superfusion model with temporary arrest of medium flow.

Hippocampal slices of rats at postnatal day 7 were submitted to superfusion with Ca(2+)- and Mg(2+)-free, bicarbonate buffered ion balanced medium, and perfusate concentrations of eicosanoids: thromboxane B2 and 6-keto prostaglandin F1 alpha were determined by the radioimmunoassay. It was noted that the permanent presence of Ca2+ increased the basal eicosanoid level, and in these conditions modulation of eicosanoid production was lost, whereas temporary, a 20 min application of 1.3 mM Ca2+ did not influence significantly eicosanoid release. A 20 min application of the anoxic/aglycemic medium containing calcium did not change the content of eicosanoids in superfusates. A significant stimulation of the thromboxane B2 and 6-keto prostaglandin F1 alpha release was noted provided the application of the experimental medium was accompanied by a 10 min arrest of superfusion. This effect was inhibited by MK-801 and quinacrine, suggesting an involvement of NMDA receptors and phospholipase A2. We propose that a model of anoxic/aglycemic superfusion with a stop flow period allows retention of endogenous glutamate in the extracellular fluid, resembling a similar effect during in vivo ischemia, whereas during a continuous superfusion glutamate is immediately washed out. Consequently, an application of the anoxic/aglycemic medium accompanied by a temporary arrest of superfusion represents more adequate in vitro model of ischemia than a constant superfusion with this medium. In these conditions NMDA receptors mediate eicosanoid release.