Abstract
BackgroundThe hippocampus undergoes apoptosis in experimental pneumococcal meningitis leading to neurofunctional deficits in learning and memory function. The aim of the present study was 1) to investigate hippocampal apparent diffusion coefficient (ADC) and volume with MRI during the course of experimental pneumococcal meningitis, 2) to explore the influence of accompanying bacteremia on hippocampal water distribution and volume, 3) and to correlate these findings to the extent of apoptosis in the hippocampus.MethodsExperimental meningitis in rats was induced by intracisternal injection of live pneumococci. The study comprised of four experimental groups. I. Uninfected controls (n = 8); II. Meningitis (n = 11); III. Meningitis with early onset bacteremia by additional i.v. injection of live pneumococci (n = 10); IV. Meningitis with attenuated bacteremia by treatment with serotype-specific anti-pneumococcal antibodies (n = 14). T2 and diffusion weighted MR images were used to analyze changes in hippocampus volume and water diffusion (ADC). The results were correlated to ADC of the cortex, to ventricular volume, and to the extent of hippocampal apoptosis.ResultsBoth ADC and the volume of hippocampus were significantly increased in meningitis rats compared to uninfected controls (Kruskal-Wallis test, p = 0.0001, Dunns Post Test, p < 0.05), and were significantly increased in meningitis rats with an early onset bacteremia as compared to meningitis rats with attenuated bacteremia (p < 0.05). Hippocampal ADC and the volume and size of brain ventricles were positively correlated (Spearman Rank, p < 0.05), whereas no association was found between ADC or volume and the extent of apoptosis (p > 0.05).ConclusionsIn experimental meningitis increase in volume and water diffusion of the hippocampus are significantly associated with accompanying bacteremia.
Highlights
The hippocampus undergoes apoptosis in experimental pneumococcal meningitis leading to neurofunctional deficits in learning and memory function
We have previously studied the role of accompanying bacteremia in detail in experimental pneumococcal meningitis and have demonstrated that this complication resulted in an attenuated Cerebrospinal fluid (CSF) pleocytosis [2], an interrupted cerebral autoregulation [3], and an increased mortality [4] as well as hippocampal apoptosis [5]
magnetic resonance imaging (MRI)-findings in the hippocampus A significant difference in Apparent diffusion coefficient (ADC) covering the total hippocampus area was demonstrated between the four experimental groups (Kruskal-Wallis test, p = 0.0001) with a significantly increased ADC in meningitis rats as compared to uninfected controls (Dunn’s post test, p < 0.05)
Summary
The hippocampus undergoes apoptosis in experimental pneumococcal meningitis leading to neurofunctional deficits in learning and memory function. The aim of the present study was 1) to investigate hippocampal apparent diffusion coefficient (ADC) and volume with MRI during the course of experimental pneumococcal meningitis, 2) to explore the influence of accompanying bacteremia on hippocampal water distribution and volume, 3) and to correlate these findings to the extent of apoptosis in the hippocampus. We have previously studied the role of accompanying bacteremia in detail in experimental pneumococcal meningitis and have demonstrated that this complication resulted in an attenuated CSF pleocytosis [2], an interrupted cerebral autoregulation [3], and an increased mortality [4] as well as hippocampal apoptosis [5]. In a study by de Jonge et al [14], MRI alterations 8–14 years after the disease were sparse, and no correlation between learning deficits and hippocampal MRI-findings could be demonstrated
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