title: Increase in hippocampal water diffusion and volume during experimental pneumococcal meningitis is aggravated by bacteremia.
abstract: BACKGROUND
  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.
  
  
  METHODS
  Experimental 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.
  
  
  RESULTS
  Both 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).
  
  
  CONCLUSIONS
  In experimental meningitis increase in volume and water diffusion of the hippocampus are significantly associated with accompanying bacteremia.
authors.affiliation: Department of Infectious Diseases, Copenhagen University Hospital Hvidovre, Kettegaard Alle 30, Hvidovre, Copenhagen 2650, Denmark. tiljon@hotmail.com.
authors.forename: Jon G
authors.initials: JG
authors.lastname: Holler
authors.forename: Christian T
authors.initials: CT
authors.lastname: Brandt
authors.forename: Stephen L
authors.initials: SL
authors.lastname: Leib
authors.forename: Ian J
authors.initials: IJ
authors.lastname: Rowland
authors.forename: Christian
authors.initials: C
authors.lastname: Østergaard
mesh_terms: D000818:Animals; D017209:Apoptosis; D016470:Bacteremia / Q000378:metabolism* / Q000382:microbiology / Q000473:pathology; D002540:Cerebral Cortex / Q000378:metabolism; D002552:Cerebral Ventricles / Q000473:pathology; D004058:Diffusion; D004195:Disease Models, Animal; D006624:Hippocampus / Q000378:metabolism* / Q000473:pathology; D008279:Magnetic Resonance Imaging; D008297:Male; D008586:Meningitis, Pneumococcal / Q000378:metabolism* / Q000473:pathology; D051381:Rats; D017208:Rats, Wistar; D013296:Streptococcus pneumoniae; D014867:Water / Q000378:metabolism*
chemical_list: D014867:Water