NOS2 gene deficiency protects from sepsis-induced long-term cognitive deficits.

To date, long-term consequences of septic encephalopathy on cerebral metabolism, cognition, learning, and memory capabilities and factors involved are poorly understood. In this study, we used a murine sepsis model to demonstrate that bacterial lipopolysaccharide (LPS) causes long-term cognitive deficits in mice. Two months after LPS treatment, wild-type mice committed more working and reference memory errors than controls. The behavioral impairment was independent of the cerebral glucose uptake as evidenced by (18)F-Fluordeoxyglucose small animal positron emission tomography. In contrast, mice deficient for the inducible nitric oxide synthase gene (NOS2-/-) did not show any cognitive changes when challenged with LPS. Immunohistochemical analysis demonstrated that LPS did not lead to neuronal cell death but caused sustained microglial activation in wild-type as compared to NOS2-/- mice. Expression analysis showed that LPS-treated NOS2-/- mice had lower brain mRNA levels for proinflammatory factors compared with wild-type mice. Expression analysis demonstrated distinct changes in the content of synaptic proteins in wild-type mice, which were not observed in the NOS2-/- mice. Together, this data set outlines the importance of the NOS2 activation for long-term cerebral changes after severe sepsis.

Sepsis causes neuroinflammation and concomitant decrease of cerebral metabolism.

BACKGROUND: Septic encephalopathy is a severe brain dysfunction caused by systemic inflammation in the absence of direct brain infection. Changes in cerebral blood flow, release of inflammatory molecules and metabolic alterations contribute to neuronal dysfunction and cell death. METHODS: To investigate the relation of electrophysiological, metabolic and morphological changes caused by SE, we simultaneously assessed systemic circulation, regional cerebral blood flow and cortical electroencephalography in rats exposed to bacterial lipopolysaccharide. Additionally, cerebral glucose uptake, astro- and microglial activation as well as changes of inflammatory gene transcription were examined by small animal PET using [18F]FDG, immunohistochemistry, and real time PCR. RESULTS: While the systemic hemodynamic did not change significantly, regional cerebral blood flow was decreased in the cortex paralleled by a decrease of alpha activity of the electroencephalography. Cerebral glucose uptake was reduced in all analyzed neocortical areas, but preserved in the caudate nucleus, the hippocampus and the thalamus. Sepsis enhanced the transcription of several pro- and anti-inflammatory cytokines and chemokines including tumor necrosis factor alpha, interleukin-1 beta, transforming growth factor beta, and monocot chemoattractant protein 1 in the cerebrum. Regional analysis of different brain regions revealed an increase in ED1-positive microglia in the cortex, while total and neuronal cell counts decreased in the cortex and the hippocampus. CONCLUSION: Together, the present study highlights the complexity of sepsis induced early impairment of neuronal metabolism and activity. Since our model uses techniques that determine parameters relevant to the clinical setting, it might be a useful tool to develop brain specific therapeutic strategies for human septic encephalopathy.