Role of pyruvate in ischaemia-like conditions on cultured neurons.

In vitro, it is known that neurons in serum free mediums survive in the absence of glucose if pyruvate is present. We exposed cultured neurons on poly-L-lysine coated dishes to 6 different concentrations of pyruvate ranging from 0 to 1000 microM combined with glucose-supplement and normoxia (controls), glucose-deprivation and normoxia (hypoglycaemia), glucose-supplement and hypoxia (hypoxia), and glucose deprivation and hypoxia (ischaemia-like conditions) for 4 h. In all these conditions, lowering pyruvate below 250 microM led to a significant decrease of neuronal survival. Even in controls, there was no surviving neurons exposed to 0 microM of pyruvate. Glucose deprivation alone did not essentially influence the survival rate. Regardless of glucose deprivation, hypoxia led to an additional 23%-100% decrease of neuronal survival. When neurons were cultured above the astrocyte layers, neurons were much more tolerant with exposure to 0 microM of pyruvate for 4 h as compared to neurons on poly-L-lysine. The results indicate that pyruvate rather than glucose is essential for the energy supply to cultured neurons, probably because these neurons are immature and possess yet little capability to gain energy from glycolysis. Astrocytes may protect neurons from pyruvate deprivation by providing energy to neurons. In neuron rich culture, ischaemia is much better simulated by hypoxia-pyruvate deprivation rather than hypoxia-glucose deprivation.