Immunohistochemical localization of nitric oxide synthase in rat anterior choroidal artery, stromal blood microvessels, and choroid plexus epithelial cells.

Nitric oxide (NO) has recently been shown to regulate blood flow to choroid plexus, a specialized brain structure responsible for production of most of cerebrospinal fluid. In the present study, we used a specific polyclonal rabbit antibody against the neuronal isoform of NO synthase (NOS), a synthetic enzyme for NO, to determine the localization of NOS in the choroid plexus of adult male Sprague-Dawley rats. NOS-containing nerve fibers were found in the anterior choroidal artery and its branches, and in stromal blood microvessels. Chronic denervation experiments indicated that these nerve fibers originate predominantly from the sphenopalatine ganglion. NOS-immunopositive staining was also detected in the cytoplasm of choroidal epithelial cells. NADPH-diaphorase, a histochemical marker for NOS, was found to colocalize with NOS-immunoreactive product in both nerve fibers and choroidal epithelium. Both neuronal and epithelium-derived NO may regulate secretory function and hemodynamics of choroidal tissue.