Meningitis induced by Streptococcus pneumoniae elicits cellular damage but not DNA damage during the acute phase of infection in the hippocampus of Wistar rats

摘要

Pneumococcal meningitis is associated with high mortality and morbidity. Great majority of survivors are affected by neurological sequelae due to a wide spectrum of brain injury mainly affecting the cortex and hippocampus. Published data suggest histomorphological observations of these sequelae indicating a pattern of brain damage characterized by necrotic tissue damage in the cerebral cortex and apoptosis of neurons in the hippocampal dentate gyrus. Aim of the present study was to investigate and correlate data for any DNA damage due to the effect of pneumococcal meningitis on the hippocampus in Wistar rats, during the acute phase of the infection. Thirty days old rats were divided into normal control (NC) and meningitis (M) groups. Rats in the meningitis group were infected with Streptococcus pneumoniae, intracisternally on postnatal day 31. The concentration of the bacterial suspension in phosphate-buffered saline (PBS) was 1×106 CFU/ml. The rats were kept under observation for 18 hrs for clinical symptoms of meningitis to develop. 10-50μl of the CSF sample was collected for confirmation by gram's staining and culture. The rats were perfused transcardially with saline followed by 10% formalin. Brains were removed, processed for paraffin sectioning and stained with cresyl violet staining. Neurodegeneration in the hippocampal CA1, CA3 and dentate hilus were quantified. DNA damage was assessed by the alkaline single-cell gel electrophoresis "comet assay" method. The hippocampal sub-regions showed neurodegeneration in the form of cellular damage. Significant fractions of neurons in the above regions were darkly stained and were irregular in shape. There was 56-81% neuronal loss in these regions. The surviving neurons showed 34-45% decrease in cell diameter and 28-29% decrease in the cross-sectional area in the hippocampal sub regions. But there were no DNA damage observed in all the regions of the hippocampus as a whole. Pneumococcal meningitis that was induced in the 30 days old rats conformed to the clinical parameters observed for meningitis and the histological analysis showed cellular damage likewise; but most interestingly there was no DNA damage in the hippocampus. This could be due to the fact that the rats were only in the acute phase of infection. Most probably, the time required for the DNA damage to occur would require that the rats proceed to a chronic phase. This finding could very well hold hope for meningitis cases that could be salvaged during the acute phase itself, thereby curtailing the neurological sequelae commonly observed after recovering from an untreated or chronic pneumococcal infection.