COMPARATIVE DISTRIBUTION OF NITRIC-OXIDE SYNTHASE-CONTAINING AND SEROTONIN-CONTAINING NEURONS IN THE RAPHE NUCLEI OF 4 MAMMALIAN-SPECIES

Monoclonal antibodies were generated against serotonin (5-HT) and the C-terminal portion of the neuronal form of nitric oxide synthase (nNOS ), the enzyme producing nitric oxide in neurons. These antibodies were used to compare the distribution of 5-HT- and nNOS-containing neurons in the raphe nuclei of four animal species (rat, mouse, guinea pig, a nd cat). It was found that the rat was the only species in which the r aphe nuclei contain a substantial number of nNOS-immunoreactive (IR) c ell bodies. In this species and as observed by other authors, all mese ncephalic raphe nuclei contained nNOS-IR cells, the largest group bein g located in the nucleus raphe dorsalis. The coexistence of nNOS and 5 -HT immunoreactivities in these nuclei was visualized by double labeli ng. In the medulla, the nuclei raphe magnus and obscurus displayed a r ather low number of nNOS-IR neurons. In the other species, nNOS-IR cel l bodies were found in very low numbers, whatever raphe nucleus was co nsidered. The rostral pole of the nucleus raphe dorsalis and the nucle i raphe magnus and obscurus contained a few nNOS-IR neurons which did not show any coincidence with the 5-HT neurons. In addition, nNOS-IR a xons were rare. It is concluded that in the mouse, guinea pig, and cat the involvement of nitric oxide in functions subserved by 5-HT within the raphe nuclei might be minimal.