LOCALIZATION OF NITRIC-OXIDE SYNTHASE IN THE MOUSE OLFACTORY AND VOMERONASAL SYSTEM - A HISTOCHEMICAL, IMMUNOLOGICAL AND IN-SITU HYBRIDIZATION STUDY

The distribution of nitric oxide synthase (NOS) in the mouse olfactory bulb and olfactory epithelium, including the vomeronasal organ, was s tudied using an anti-NOS antibody, NADPH diaphorase histochemistry and in situ hybridization with NOS specific antisense oligonucleotide pro bes. Interneurons containing NOS protein and mRNA, and exhibiting NADP H diaphorase activity were detected in the plexiform layer of the main olfactory bulb and the granule cell layer of main and accessory olfac tory bulbs. Periglomerular cells and granule cells in the main olfacto ry bulb were also NOS positive with diaphorase and immunostaining for NOS. In contrast, no evidence for NOS expression was found either in t he main olfactory epithelium or in the vomeronasal organ, in spite of the strong diaphorase staining of the surface of the main olfactory ep ithelium. Polymerase chain reaction amplification experiments for dete ction of NOS gene expression further indicated that NOS is expressed i n the olfactory bulb but not in either the main olfactory epithelium o r vomeronasal organ. Use of an antibody raised against another enzyme, NADPH-P450 oxidoreductase, showed that this protein was strongly expr essed in the olfactory epithelium, Activity of this enzyme may account for the diaphorase histochemical staining of the epithelia. An involv ement of neuronal nitric oxide synthase in signalling in olfactory rec eptor neurons is therefore doubtful, although NOS is clearly expressed in neurons in both main and accessory olfactory bulbs.