Intracerebral microdialysis of glutamate and aspartate in two vascular territories after aneurysmal subarachnoid hemorrhage

CEREBRAL ISCHEMIA ASSOCIATED with subarachnoid hemorrhage may have severe consequences for neuronal functioning. The excitatory amino acid neurotransmitters glutamate and aspartate have been shown to be of particular importance for ischemia and ischemic neuronal damage. For seven patients who underwent early surgery for ruptured intracranial aneurysms, intracerebral microdialysis of glutamate and aspartate was performed to monitor local metabolic changes in the medial temporal (all seven patients) and subfrontal cortex (Patients 4 through 7). Samples were collected every 30 or 60 minutes, using an autosampler. The results show that extracellular glutamate and aspartate concentrations can rise to very high levels after surgery for subarachnoid hemorrhage and aneurysm. These increased levels of excitatory amino acids correlated well with the clinical course and neurological symptoms of the patients. Simultaneous sampling from two vascular territories (middle cerebral artery and anterior cerebral artery) also showed that a rise in extracellular glutamate and aspartate in one territory is not necessarily parallel with a rise in the other. The application of the microdialysis technique with an on-line assay system might be of value in the future for continuous monitoring of ischemic events to optimize treatment with, for example, blockers of glutamatergic neurotransmission.