ELECTRON-MICROSCOPIC LOCALIZATION OF NITRIC-OXIDE-I-SYNTHASE IN THE ORGAN OF CORTI OF THE GUINEA-PIG

Nitric oxide synthase (NOS) activity has been detected previously in t he mammalian cochlea at a light microscopic level. Here we present res ults of electron microscopic analysis for post-embedding immunoreactiv ity of neural-type NOS I in the cochlea of the guinea pig. Strong enzy me immunoreactivity was identified in the cytoplasm of inner and outer hair cells. Gold-labeled NOS I antibodies were mainly located in elec tron-dense areas of the cytoplasm, whereas electron-lucent regions of tile receptor cells were nearly free from any immunoreactivity. In bot h types of hair cells anti-NOS I antibodies were also visible in the c uticular plates, hair bundles end nuclei. Further ultrastructure analy sis revealed that the submembranous cisternae of the outer hair cells were nearly free from any reaction product, demonstrating that the who le cytoplasm of this hair cell was nor immunoreactive. Other NOS I imm unoreactivity was identified in the cuticular plates of the inner and outer pillar cells and in the cytoskeletal elements located in the api cal parts of Deiter cells, forming the lamina reticularis or in cytosk eletal-containing regions in basal Deiter cells. Anti-NOS antibodies w ere visible in the nuclei of various cell types. Our findings suggest that nitric oxide produced by NO I synthase in the organ of Corti may act as a modulator of hair cell physiology during the processes of sig nal transduction with frequence selectivity.