Pneumococcal meningitis induced neuronal injury in Wistar rats - a study on neurodegenerative changes in the sub-regions of the hippocampus

Background Bacterial meningitis is known to cause neurodegenerations in the hippocampus, motor cortex and cerebellum. The aim of the present study was to investigate quantitatively the effect of pneumococcal meningitis on hippocampal sub-regions in Wistar rats. Method Thirty-day 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 (colony forming units/ml). The rats were kept under observation for 18 hours for clinical symptoms of meningitis to develop. After 18-24 hours of incubation, 10-50μl of the CSF (cerebrospinal fluid) sample was collected. Gram's staining of the CSF smear was done and observed under oil immersion objective (100X) for Gram positive, lanceolate diplococci. The rats were perfused transcardially with saline followed by 10% formalin. Brains were removed, processed for paraffin sectioning and stained with cresyl violet stain. Neurodegeneration in the hippocampal CA1, CA3 and dentate hilus were quantified. Results The hippocampal sub-regions showed neurodegeneration. 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. Conclusion Meningitis affects the hippocampal subregions equally and may be the neural basis of cognitive deficit. The mechanism of such neurodegeneration could have been due to necrosis or apoptosis.