DIFFERENTIAL DISTRIBUTION OF NICOTINAMIDE ADENINE-DINUCLEOTIDE PHOSPHATE-DIAPHORASE AND NEURAL NITRIC-OXIDE SYNTHASE IN THE RAT CHOROID-PLEXUS - A HISTOCHEMICAL AND IMMUNOCYTOCHEMICAL STUDY

This study used NADPH diaphorase (NADPHd) histochemistry and neuronal nitric oxide synthase immunocytochemistry to examine the localization of nitric oxide synthase in the choroid plexus of the lateral ventricl es and the fourth ventricle of rat brain. That the NADPHd reaction pro duct in choroid plexus was specific to nitric oxide synthase was evalu ated: (i) by comparison to immunocytochemical labelling for nitric oxi de synthase; and (ii) by comparing NADPHd histochemical staining in ch oroid plexus and brain (rich in nitric oxide synthase-positive and NAD PHd-positive neurons) in the presence or absence of iodonium diphenyl or dichlorophenolindophenol, two potent albeit non-selective inhibitor s of nitric oxide synthase activity. In brain, NADPHd histochemistry h omogeneously stained neuronal cell bodies, axons and dendrites, while it produced particulate cytoplasmic staining of all epithelial cells i n the choroid plexuses of the lateral and fourth ventricles. Within th e choroid plexus of the lateral ventricles, NADPHd-positive nerve fibr es were also observed around blood vessels and coursing among the epit helial cells. The distribution of immunoreactivity for nitric oxide sy nthase in brain and in nerve fibres in the choroid plexuses of the lat eral ventricles resembled the distribution of histochemical labelling for NADPHd. Choroid plexus epithelial cells were, however, devoid of n itric oxide synthase immunoreactivity. Consistent with this, iodonium diphenyl and dichlorophenolindophenol (0.1 mM) inhibited NADPHd histoc hemical staining in brain neurons and in choroid plexus nerve fibres, but not in choroid plexus epithelial cells. These results demonstrate that the choroid plexus of the lateral ventricles in rat brain is inne rvated by nitric oxide synthase-positive nerve fibres. These nitric ox ide synthase-positive nerve fibers may have an important role in the r egulation of cerebrospinal fluid balance. Although choroid plexus epit helial cells contain an enzyme with NADPHd activity, this enzyme is no t nitric oxide synthase.