Cortical Excitatory Amino Acid Release and Cell Function during Hypotension in Near-Term Born Lambs

Abstract

Background: Energy failure due to insufficient cerebral O₂-supply leads to excess accumulation of calcium ions in presynaptic neurons, followed by excess release of excitatory amino acids, which are potent neurotoxins, into the synaptic cleft. Aim:To investigate whether electrocortical brain activity (ECBA) can provide an adequate measure for excitatory amino acid release due to hemorrhagic hypotension. Methods: Ten near-term lambs were delivered at 127 days of gestation (term: 147 days). After a stabilization period, hypotension was induced by stepwise withdrawal of blood. Cerebral microdialysis was used to measure the concentrations of glutamate and aspartate. Results:During hypotension, mean arterial blood pressure, cerebral O₂-supply and ECBA decreased and the extracellular concentration of glutamate increased significantly. ECBA was significantly related to glutamate (R²: 0.67, p < 0.001) and aspartate (R²: 0.57, p < 0.001) concentrations. Conclusion:The extracellular release of glutamate and aspartate in the cerebral cortex increases after hemorrhagic hypotension in near-term born lambs. The extracellular overflow of glutamate and aspartate were significantly inversely related to ECBA.