EFFECT OF EXPERIMENTAL ESCHERICHIA-COLI MENINGITIS ON CONCENTRATIONS OF EXCITATORY AND INHIBITORY AMINO-ACIDS IN THE RABBIT BRAIN - IN-VIVOMICRODIALYSIS STUDY

Excessive extracellular fluid concentrations of the amino acids glutam ate and aspartate play an important role in the pathogenesis of neuron al cell damage during hypoxia, hypoglycemia, and seizure. The purpose of these investigations was to test the hypothesis that bacterial meni ngitis causes progressive increase in excessive extracellular fluid co ncentrations of excitatory and inhibitory neurotransmitters. To test t his hypothesis, Escherichia coli was injected intracisternally in juve nile 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 t he excessive extracellular fluid of animals injected with E. coli comp ared with control animals injected with saline. However, concentration s of these excitatory and inhibitory amino acids rose late in the cour se of meningitis, at a time when the animals were hypotensive (mean bl ood pressure less-than-or-equal-to 40 mm Hg). These data show that the major increase in excitatory neurotransmitters during experimental me ningitis occurs in association with the cerebral ischemia produced by septic shock rather than being produced by the meningitis itself.