The aim of the study is test the hypotheses that NO from nNOS or iNOS sensitises brain neurons to hypoxic damage, and if so whether this is mediated by NO/O2 competition at cytochrome c oxidase. The work will use isolated brain cells (neurons, astrocytes, and microglia) from neonatal rats, cultured together or separately, to test whether NO from glial iNOS or neuronal nNOS synergises with hypoxia to induce neuronal death. Nitric oxide (NO) inhibits mitochondrial cytochrome c oxidase (COX) in competition with oxygen. Thus, NO may sensitise cells to hypoxic damage, as inhibition of COX rapidly causes neuronal death (e. g. during stroke).
The brain produces low levels of NO from nNOS in neurons activated by glutamate, and produces high levels of NO from iNOS after inflammatory activation of glial cells. Activated glia can kill neurons in culture, and may do so in vivo in a wide range of CNS pathologies. This may be the common cause of neuronal death in many brain diseases. Inflamed glia can kill co-cultured neurons in part via NO from glial iNOS inhibiting neuronal COX. Because this NO inhibition is competitive with oxygen it follows that neurons surrounded by inflamed glia may be more sensitive to hypoxia.
This project thus tests whether NO from nNOS or iNOS sensitises neurons to hypoxic damage via NO/O2 competition at COX. Cultured neurons or brain slices will be exposed to either exogenous or endogenous NO, and at the same time exposed to hypoxia, in order to test whether NO sensitises neurons to hypoxia. The mechanism of such sensitisation will be investigated using NOS inhibitors and interventions such as light that block NO binding to COX.
The ability of inflammation induced by bacterial endotoxin, cytokines, ?-amyloid and hypoxia itself to sensitise neurons to subsequent hypoxia will be studied. A range of chemicals will be tested for their ability to block such death, and thus potentially be developed as therapeutic drugs or strategies.
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