Glia
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The primary olfactory nerves provide uninterrupted conduits for neurotropic pathogens to access the brain from the nasal cavity, yet infection via this route is uncommon. It is conceivable that olfactory ensheathing cells (OECs), which envelope the olfactory nerves along their entire length, provide a degree of immunological protection against such infections. We hypothesized that cultured OECs would be able to mount a biologically significant response to bacteria and pathogen-associated molecular patterns (PAMPs). ⋯ Immunostaining for the chemokine Gro demonstrated a functional response that was consistent with NF kappaB activation. OECs expressed mRNA for Toll-like receptors (TLRs) 2 and 4, but only TLR4 protein was detected by Western blotting and immunohistochemistry. The results demonstrate that OECs possess the cellular machinery that permits them to respond to certain bacterial ligands, and may have an innate immune function in protecting the CNS against infection.
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Aquaporin-4 (AQP4), a water channel protein, is abundantly expressed in astrocytes and plays a key role in the development of brain edema. However, it is not clear whether AQP4 contributes to astrocytic swelling in hypoxia-ischemia (HI). To investigate the roles of AQP4 in astrocytic swelling during HI and reoxygenation, we measured AQP4 expression and astrocytic cellular volume in cultured rat astrocytes following HI and reoxygenation. ⋯ The different roles of AQP4 during HI and reoxygenation suggest that AQP4 knockdown may protect against water influx in the formation of astrocyte swelling during HI, and may also delay water clearance in the resolution of astrocyte swelling during reoxygenation. In conclusion, AQP4 mediates bidirectional transport of water across astrocytes during HI and reoxygenation. AQP4 manipulation may serve as a novel therapeutic strategy during different periods of hypoxic-ischemic brain edema in neonates.