DISTRIBUTION OF NADPH-DIAPHORASE IN THE CEREBRAL BLOOD-VESSELS OF RATS - A HISTOCHEMICAL-STUDY

NADPH-diaphorase (neuronal nitric oxide synthase) activity in the cere bral blood vessels was investigated by light and electron microscopic histochemistry to elucidate the sites of nitric oxide production. Netw orks of adventitial nerves containing NADPH-diaphorase were distribute d in all parts of the circle of Willis. However, NADPH-diaphorase acti vity in adventitial nerves was much sparser in the region of the poste rior cerebral artery, and absent in the pial arteries smaller than 100 mum in diameter. Endothelial cells were intensely stained in arteries and arterioles. These results support the hypothesis that vascular to ne is regulated by nitric oxide, which is derived from endothelial cel ls and adventitial nerves.