Immunoelectron microscopic localization of nitric oxide synthase III in the guinea pig organ of Corti

Nitric oxide synthase III (NOS III) was identified in the guinea pig cochle a on an ultrastructural level using a post-embedding immunolabeling procedu re. Ultrathin sections of London Resin (LR) White-embedded specimens were i ncubated with various concentrations of a commercially available antibody t o NOS III and the immunoreactivity visualized by a gold-labeled secondary a ntibody. Analysis of ultrathin sections of the organ of Corti in the second turn of the cochlea showed that NOS III could be localized in the endothel ial cells of the blood vessels under the basilar membrane, which was compar able to its location in similar cells types in various biological systems. Besides this, NOS III was also found in the cytoplasm and in the nuclei of inner and outer hair cells. Immunoreactivity was not distributed homogeneou sly within receptor cells. Numerous gold particles could be identified at t he border of the cuticular plates, in the middle parts of the stereocilia a nd in the cytoplasm. Gold-labeled anti-NOS III antibodies in these sites we re seen mostly on the cytoplasmic side of the submembranous cisterns in the vicinity of mitochondria and in the central parts of the hair cells, where as the cisterns were nearly free from any immunoreactivity. NOS III was als o detected in the efferent and afferent nerve endings that were located at the basal and basolateral side of the outer hair cells. Some immunoreactivi ty was visible in different nerve fibers of the inner and outer spiral tunn els. Besides this, gold-labeled antibodies were also present in the cuticul ar plate of inner and outer pillar cells, in the cytoskeletal elements loca ted in the apical parts of Deiters cells, forming the lamina reticularis, a nd in the cytoskeletal-containing region of the cytoplasm of those Deiters cells located at the basal side of the outer hair cells. The role of the NO S III immunoreactivity identified in the organ of Corti was consistent with respect to hair cell and tissue modulation.