Periventricular leukomalacia (PVL) is the main cause of neurologic handicap in pre-term infants. The understanding of cellular and molecular mechanisms leading to white matter damage is critical for development of innovative therapeutic strategies for PVL. The pathogenesis of PVL remains unclear but possibly involves glutamate excitotoxicity as an important molecular pathway. We previously described a neonatal mouse model of excitotoxic white matter lesion mimicking human PVL. In the present study, we used this experimental tool to investigate the cellular populations and the glutamate receptor subtypes involved in excitotoxic white matter lesions. Combined immunohistochemical, electron microscopic, and cell death detection data revealed that microglial activation and astrocytic death were the primary responses of white matter to excitotoxic insult. In vitro experiments suggested that microglia activated by ibotenate released soluble factors that kill astrocytes. The use of selective agonists and antagonists of glutamate receptors revealed that N-methyl-D-aspartate (NMDA) receptor activation was essential and sufficient to produce cystic white matter lesions. NMDA receptor immunohistochemistry labeled microglial cells in the neonatal periventricular white matter. The developing white matter displayed a window of sensitivity to excitotoxic damage that was paralleled by the transient presence of NMDA receptor-expressing white matter cells. Assuming that similar pathophysiologic mechanisms are present in human pre-term infants, microglia and NMDA receptors could represent key targets for treatment of PVL.ibotenate was administered at post-natal day (P) 0 to P2. In contrast, ibotenate injected at P5 or P10 killed neurons in all cortical layers. Furthermore, ibotenate at P2 and P5 induced periventricular white matter cystic lesions mimicking several aspects of human cystic PVL.Using our mouse paradigm of excitotoxic white matter lesions, the present study aimed to determine the cellular cascade leading to periventricular cystic lesions. The contribution of the different glutamate receptors was also addressed. Materials and MethodsAnimals and drug administration. Swiss pups (n = 456) and transgenic C57bl / 6xDBA 2 pups (n = 47) expressing the lacZ reporter gene under the control of plp regulatory sequences were used for the experiments. The plp gene encodes the proteolipid proteins and its alternatively spliced product DM-20, which are major proteins of central nervous system myelin. Previous work with this transgenic line indicates that, both in vivo and in vitro, the transgene is expressed by O4-positive pre-oligodendrocytes and by RIP-positive differentiated oligodendrocytes, but not by neuronal cells, astrocytes, or radial glial cells (46). Furthermore, the pattern of beta-galactosidase expression is similar and superimposable on the expression pattern of endogenous plp/dm-20 (46). These transgenic mice were used to study the outcome of the oligodendroglial lineage following ibotenate injections.

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Natriuretic peptides of various forms are present in animals and plants, and display structural similarities to cyclic antibacterial peptides. Pretreatment of Pseudomonas aeruginosa PAO1 with brain natriuretic peptide (BNP) or C‐type natriuretic peptide (CNP) increases bacterium‐induced glial cell necrosis. In eukaryotes, natriuretic peptides act through receptors coupled to cyclases. We observed that stable analogs of cAMP (dibutyryl cAMP) and cGMP (8‐bromo‐cGMP) mimicked the effect of brain natriuretic peptide and CNP on bacteria. Further evidence for the involvement of bacterial cyclases in the regulation of P. aeruginosa PAO1 cytotoxicity by natriuretic peptides is provided by the observed doubling of intrabacterial cAMP concentration after exposure to CNP. Lipopolysaccharide (LPS) extracted from P. aeruginosa PAO1 treated with both dibutyryl cAMP and 8‐bromo‐cGMP induces higher levels of necrosis than LPS extracted from untreated bacteria. Capillary electrophoresis and MALDI‐TOF MS analysis have shown that differences in LPS toxicity are due to specific differences in the structure of the macromolecule. Using a strain deleted in the vfr gene, we showed that the Vfr protein is essential for the effect of natriuretic peptides on P. aeruginosa PAO1 virulence. These data support the hypothesis that P. aeruginosa has a cyclic nucleotide‐dependent natriuretic peptide sensor system that may affect virulence by activating the expression of Vfr and LPS biosynthesis.