Nitric oxide synthase in reactive astrocytes adjacent to beta-amyloid plaques

This study provides the first evidence that nitric oxide is released by astrocytes surrounding beta-amyloid plaques. Nitric oxide is involved in many neuropathological conditions and can have either a neuroprotective or a neurotoxic function depending on its concentration and the redox state of the tissue. It is produced by the enzyme nitric oxide synthase, which can be located by a simple histochemical technique for demonstrating NADPN diaphorase. Using tills method we examined tissue from EO brains where there were varying numbers of beta-amyloid plaques in the cerebral cortex, In the 6 brains with moderate or high densities of plaques, primitive and cored plaques were associated with between 1 and 10 reactive astrocytes that contained NADPH diaphorase or were immunoreactive for the inducible form of nitric oxide synthase. In the 4 brains which had only low densities of plaques, the plaques were not associated with diaphorase-containing astrocytes. The percentage of plaques associated with 1 or more NADPH diaphorase-containing astrocyte varied between 1 and 21% and was col-related with the density of plaques. Astrocytes were the only for-m of NADPN diaphorase-positive glial cell associated with the plaques. There was no evidence of any nitric oxide synthase occurring in microglia. (C) 1997 Academic Press.