NEURONS SYNTHESIZING NITRIC-OXIDE INNERVATE THE MAMMALIAN CAROTID-BODY

The carotid body is an arterial chemoreceptor organ sensitive to blood levels of O2, CO2 and pH. The present immunocytochemical and neuroche mical study has demonstrated the presence of an extensive plexus of ni tric oxide (NO)-synthesizing nerve fibers in this organ. These nitric oxide synthase (NOS)-containing axons are closely associated with pare nchymal type I cells and with blood vessels in the carotid body. Dener vation and retrograde tracing experiments have revealed that these fib ers arise from NOS-immunoreactive and nicotinamide adenine dinucleotid e phosphate (NADPH) diaphorase-positive neuronal cell bodies located i n the petrosal ganglion and the carotid body, and dispersed along the glossopharyngeal and carotid sinus nerves (CSN). Within the petrosal g anglion, these neurons are topographically segregated from the catecho laminergic cells, and they contain the neuropeptide, substance P. NOS- positive autonomic microganglial cells in the carotid body and CSN als o exhibit choline acetyltransferse (ChAT) immunoreactivity. Our result s suggest that nitric oxide may be a novel neuronal messenger in the m ammalian carotid body involved in the modulation of chemosensory trans duction and transmission in this organ. (C) 1993 Wiley-Liss, Inc.