Approximately 15,000 cases of bacterial meningitis occur each year in the United States. The disease continues to be fatal in many patients and to cause neurologic sequelae in up to 30% of the survivors. Neonatal meningitis, caused in most cases by either group B Streptococcus or by Escherichia coli, has a particularly high mortality (15%-35%, depending on the age at onset) and morbidity (only 50% of survivors are neurologically normal). The spectrum of neurologic sequelae in neonates with meningitis and histopathologic studies indicate that injury to neurons is an important consequence of the disease, but little is known about the mechanisms that lead to neuronal injury. The long term goal of the proposed research is to understand in detail the processes that lead to neuronal injury during meningitis in order to be able to develop therapies that can preserve neuronal function. Based on preliminary experimental studies by us and others, the hypothesis has been formulated that soluble factors resulting from the inflammation and hypoxic/ischemic changes in the brain potentiate each other's harmful effects on neurons. In the present proposal this hypothesis will be tested by using both an animal model of neonatal meningitis caused by group B Streptococcus and an in vitro system using primary vortical neurons. In a first set of experiments, the histopathology of neonatal meningitis will be defined in an infant rat model. The brains of pups with acute meningitis and of pups surviving the disease after treatment with antibiotics will be studied by routine light microscopy and immunocytochemistry for evidence of brain injury, such as infiltration by inflammatory cells, loss of neurons, decreased density of synapses, and reactive changes of microglia and astrocytes. In a subsequent study, the same animal model will be used to examine whether inflammation associated with meningitis and hypoxia potentiate each other in causing brain damage. Brain damage will be measured again by light microscopy and by the expression of heat shock protein 72, a marker for neuronal stress caused by hypoxia/ischemia. The extent of brain damage will be compared in animals with meningitis, in animals subjected to hypoxia, and in animals subjected to both hypoxia and meningitis. An exacerbation of brain injury in the latter group beyond the extent expected based on animals subjected to meningitis or hypoxia alone would lend support to the hypothesis of an additive effect of inflammation and hypoxia. In the last set of experiments, primary cultures of rat cortical neurons will be used to study in vitro the effects of inflammation and hypoxia on neurons. Cultured neurons will be exposed to infected cerebrospinal fluid from animals with meningitis or to individual inflammatory and bacterial products in the absence or presence of simulated hypoxia/ischemia and cytotoxicity under these different conditions will be determined. Again, these studies will assess whether inflammatory products and hypoxia/ischemia have additive neurotoxic effects in vitro.
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