Characterization and regional distribution of nitric oxide synthase in thehuman brain during normal ageing

Nitric oxide (NO) is a highly diffusible cellular mediator generated from L -arginine by the enzyme nitric oxide synthase (NOS). As little is known abo ut the regional distribution of NOS in the human brain, we examined the dis tribution pattern of nitric oxide synthase activity in 28 regions of the hu man brain using the [H-3]L-citrulline formation assay. To elucidate which i soforms contribute to the total NOS activity we performed Western blot anal ysis of neuronal, inducible and endothelial NOS. We further determined brai n levels of arginine and citrulline as a potential index of NOS activity pr e mortem. NOS activity appears to remain unaltered during ageing and is ind ependent of post mortem delay,,gender or sample storage time. We identified a regional pattern of NOS distribution with highest levels of NOS activity in the substantia innominata, cerebellar cortex, nucleus accumbens and sub thalamicus, whereas lowest levels were measured in the corpus callosum, tha lamus, occipital cortex, and dentate nucleus, nNOS was measured throughout the brain, in contrast iNOS and eNOS were not detectable. We therefore conc lude that primarily nNOS is responsible for NOS activity in the human brain . Levels of citrulline were higher than those of arginine, but did not corr elate with the enzyme activity, suggesting that these parameters are unsuit able for testing NOS activity premortem. The characterization and topograph ical pattern of NOS in the human brain during normal ageing may assist our understanding of the physiological role of NO and its relevance in Parkinso n's and Alzheimer's disease, alcoholism, schizophrenia and AIDS. (C) 1999 E lsevier Science B.V. All rights reserved.