Effects of experimental Neisseria meningitis W135 infection on serotoninergic parameters in mice

This study investigated the effects of Neisseria menigitidis W135 infection via intraperitoneal route on plasma free tryptophan concentration, brain serotonin and 5-hydroxyindole acetic acid (5-HIAA) levels in albino mice fed normal and tryptophan-enriched diets. The kinetics of appearance of viable bacteria in the blood, brain and liver following infection were also investigated. The serotoninergic parameters were determined by colorimetric and HPLC methods while colony counts were measured by plate count technique. Compared to normal diet, the tryptophan-enriched diet resulted in significantly (P<0.05) higher level of plasma free tryptophan level irrespective of infection but with time-point increase in death score (8.3–66.7%) in the infected mice. Despite dietary tryptophan enrichment, the infected mice were also observed to elicit a time-dependent significant (P < 0.05) decrease in brain serotonin (253.9–131.4 vs. 262.4–283.7 ng/g tissue) but increase in 5-HIAA (71.8–174.5 ng/g vs. 70.4– 79.6 ng/g tissue) compared to uninfected animals. Establishment of N. meningitidis W135 meningitis in mice and subsequent brain serotonin depletion was further found to display a dose-dependent effect at 6–12 h post infection when inoculation with 104 and 106–107 cfu/ml were compared. Viable bacteria also appeared at different time-points in the blood, brain and liver of the infected mice with growths in blood and brain exhibiting similar kinetics but a disparity of 0.2–1.2 logarithmic cfu/ml. The results of this study strongly support the involvement of altered serotoninergic activity in meningococcal infection due to N. meningitidis