Synaptic activity and triphenyltetrazolium chloride metabolism are correlated after oxygen–glucose deprivation in acute, but not cultured, hippocampal slices

The importance of the hippocampus to learning and memory has attracted significant attention to how the structure responds to damage. Although many studies have used either the acute hippocampal slice preparation or organotypic hippocampal slice cultures, little work has been done to determine if the choice of model is an important variable. The present study examined whether differences exist in how each model responds to a commonly studied ischemic-like paradigm, oxygen–glucose deprivation. Following the insult, synaptic activity was examined by recording orthodromically evoked CA1 subfield responses, while mitochondrial activity was assessed by spectrophotometric measurement of formazan produced by metabolism of 2,3,5-triphenyltetrazolium chloride. The insult significantly decreased both synaptic and mitochondrial activity within acutely prepared slices, but a disparity existed between these measures in cultured slices. While evoked activity was greatly reduced by an insult of moderate duration, a much longer period was required to cause a comparable decrease in formazan production. Quantitative immunoblotting revealed that one possible explanation for the discrepancy was an elevated expression of astrocytes, which display resistance to hypoxia–aglycemia. Our data indicate that acutely prepared and cultured slices respond differently to ischemic-like challenge; therefore, assays examining viability in these models must consider their innate differences.