Effect of Experimental Escherichia coli Meningitis on Concentrations of Excitatory and Inhibitory Amino Acids in the Rabbit Brain: In Vivo Microdialysis Study

Abstract

Excessive extracellular fluid concentrations of the amino acids glutamate and aspartate play an important role in the pathogenesis of neuronal cell damage during hypoxia, hypoglycemia, and seizure. The purpose of these investigations was to test the hypothesis that bacterial meningitis causes progressive increase in excessive extracellular fluid concentrations of excitatory and inhibitory neurotransmitters. To test this hypothesis, Escherichia coli was injected intracisternally in juvenile rabbits after which neurotransmitter concentrations were measured with in vivo microdialysis. The data showed significant elevation of the excitatory amino acids aspartate and glutamate, as well as of the inhibitory neurotransmitters gamma-amino butyric acid and taurine in the excessive extracellular fluid of animals injected with E. coli compared with control animals injected with saline. However, concentrations of these excitatory and inhibitory amino acids rose late in the course of meningitis, at a time when the animals were hypotensive (mean blood pressure < or = 40 mm Hg). These data show that the major increase in excitatory neurotransmitters during experimental meningitis occurs in association with the cerebral ischemia produced by septic shock rather than being produced by the meningitis itself.