The mood-stabilizer lithium prevents hippocampal apoptosis and improves spatial memory in experimental meningitis.

Pneumococcal meningitis is associated with high morbidity and mortality rates. Brain damage caused by this disease is characterized by apoptosis in the hippocampal dentate gyrus, a morphological correlate of learning deficits in experimental paradigms. The mood stabilizer lithium has previously been found to attenuate brain damage in ischemic and inflammatory diseases of the brain. An infant rat model of pneumococcal meningitis was used to investigate the neuroprotective and neuroregenerative potential of lithium. To assess an effect on the acute disease, LiCl was administered starting five days prior to intracisternal infection with live Streptococcus pneumoniae. Clinical parameters were recorded, cerebrospinal fluid (CSF) was sampled, and the animals were sacrificed 42 hours after infection to harvest the brain and serum. Cryosections of the brains were stained for Nissl substance to quantify brain injury. Hippocampal gene expression of Bcl-2, Bax, p53, and BDNF was analyzed. Lithium concentrations were measured in serum and CSF. The effect of chronic lithium treatment on spatial memory function and cell survival in the dentate gyrus was evaluated in a Morris water maze and by quantification of BrdU incorporation after LiCl treatment during 3 weeks following infection. In the hippocampus, LiCl significantly reduced apoptosis and gene expression of Bax and p53 while it increased expression of Bcl-2. IL-10, MCP-1, and TNF were significantly increased in animals treated with LiCl compared to NaCl. Chronic LiCl treatment improved spatial memory in infected animals. The mood stabilizer lithium may thus be a therapeutic alternative to attenuate neurofunctional deficits as a result of pneumococcal meningitis

Cyto-/chemokine concentrations in cerebrospinal fluid samples of rats with pneumococcal meningitis and treated with NaCl or LiCl were measured 18 h after infection.

<p>All cyto-/chemokines measured were elevated in infected animals receiving LiCl compared to their littermates receiving NaCl. For TNF (<b>A</b>), IL-10 (<b>B</b>), and MCP-1 (<b>C</b>) this difference reached statistical significance. (TNF, tumor necrosis factor; IL, interleukin; MCP-1, monocyte chemoattractant protein 1; boxes extend from the 25th to 75th percentiles and include median; +, mean; whiskers, minimum to maximum value; *, p<0.05; **, p<0. 01).</p

Cortical damage was quantified 42 h after induction of bacterial meningitis in cryosections.

<p>(<b>A</b>) LiCl treatment reduced cortical injury without reaching statistical significance when compared to littermates treated with NaCl. (<b>B</b>) The effect was below statistical significance when comparing animals with lithium serum concentrations ≥0.4 mmol/l to NaCl treated littermates. (Boxes extend from the 25th to 75th percentiles and include median; +, mean; whiskers, minimum to maximum value).</p

At the time of sacrifice, lithium concentrations in serum and cerebrospinal fluid (CSF) of infected animals show a significant correlation (r = 0.91; p<0.0001; n = 15).

<p>At the time of sacrifice, lithium concentrations in serum and cerebrospinal fluid (CSF) of infected animals show a significant correlation (r = 0.91; p<0.0001; n = 15).</p

Cyto-/chemokine levels were measured in cerebrospinal fluid samples of infant rats 18 h after infection.

a<p>values are mean ± standard deviation (median, min., max.);</p>b<p>lithium serum conc. 0.4 mmol/l – 1.5 mmol/l;</p>c<p>non-parametric distribution; *, p<0.05; **, p<0.01; TNF, tumor necrosis factor; IL, interleuki n; MCP-1, monocyte chemoattractant protein 1; MIP-1α, macrophage inflammatory protein 1 α; IFN-γ, interferon gamma.</p><p>Cyto-/chemokine levels were measured in cerebrospinal fluid samples of infant rats 18 h after infection.</p

Three weeks after infection, the effect of chronic lithium treatment was evaluated in a water maze.

<p>In training trials, the treatment had no effect on time and distance to reach the platform on day 4.</p>a<p>values are median (25% percentile, 75% percentile);</p>b<p>Mann-Whitney test; PM, pneumococcal meningitis.</p><p>Three weeks after infection, the effect of chronic lithium treatment was evaluated in a water maze.</p

Learning capacity was assessed in the Morris water maze after 4 training days.

<p>In probe trials, the mean distance of the animals to the previous location of the platform was calculated. LiCl led to a significantly improved learning capacity compared to NaCl on day 5 (2way ANOVA). In post-hoc analysis, the effect of LiCl treatment was significant in infected animals (PM+) while it remained below statistical significance in mock-infected animals (PM−). (Boxes extend from the 25th to 75th percentiles and include median; +, mean; whiskers, minimum to maximum value; *p<0.05).</p

Apoptosis in the hippocampal dentate gyrus of survivors of bacterial meningitis was quantified in cryosections 42 h after infection.

<p>(<b>A</b>) LiCl treatment reduced apoptosis significantly compared to littermates treated with NaCl. (<b>B</b>) Hippocampal apoptosis was significantly attenuated in animals with lithium serum concentrations ≥0.4 mmol/l compared to NaCl treated littermates. (<b>C</b>) A dose-dependent effect of LiCl on hippocampal apoptosis is observed (r = −0.43, p<0.001, n = 55). (<b>C</b>) Lithium serum concentration and apoptosis in infected rats treated with 2–63 mg/kg LiCl correlate weakly (r = −0.28, p = 0.04, n = 55). (Boxes extend from the 25th to 75th percentiles and include median; +, mean; whiskers, minimum to maximum value; *, p<0.05).</p

A significant effect of chronic lithium treatment was observed in a water maze after 4 training days.

<p>In a probe trial on day 5 animals treated with lithium swum closer to the previous location of the platform.</p>a<p>values are mean ± SD;</p>b<p>2way ANOVA;</p>c<p>Sidak’s multiple comparisons test;</p>d<p>median (minimum, maximum); PM, pneumococcal meningitis;</p><p>*p<0.05;</p><p>**p<0.01.</p><p>A significant effect of chronic lithium treatment was observed in a water maze after 4 training days.</p

Gene expression of proteins involved in apoptotic pathways was analyzed in hippocampi of 13 days old rats.

<p>In mock-infected animals (PM−), gene expression of Bax, Bcl-2, and p53 was not significantly altered by LiCl treatment during 5 days. LiCl treatment significantly reduced gene expression of pro-apoptotic proteins Bax and p53 42 h after induction of meningitis (PM+). Gene expression of the anti-apoptotic Bcl-2 was increased in the LiCl group compared to NaCl. (Boxes extend from the 25th to 75th percentiles and include median; whiskers, minimum to maximum value; <i>bcl2</i>, B-cell lymphoma protein-2; <i>bax</i>, Bcl-2-associated X protein; <i>tp53</i>: tumor protein p53; *, p<0.05; **, p<0.01).</p