CHANGES IN THE DISTRIBUTION OF NITRIC-OXIDE SYNTHASE IMMUNOREACTIVE NERVE-FIBERS IN THE CHRONICALLY HYPOXIC RAT CAROTID-BODY

The distribution of nitric oxide synthase (NOS) immunoreactive nerve f ibers in the carotid body was compared between normoxic and chronicall y hypoxic rats (10% O-2 and 3.0-4.0% CO2 for 3 months). NOS immunoreac tive fibers appeared as thin processes with many varicosities. They we re distributed predominantly around small arteries and arterioles, and around clusters of glomus cells. When expressed by the density of var icosities per unit area in the parenchyma, the density of NOS fibers a ssociated with the vasculature and with the glomus cells in the chroni cally hypoxic carotid bodies was significantly decreased. Because nitr ic oxide (NO) is an inhibitory neuronal messenger in the normoxic caro tid body, the present findings suggest that the sensory mechanisms in the hypoxic carotid body may be involved in 'disinhibition' resulting from reduced NO synthesis. (C) 1998 Elsevier Science B.V. All rights r eserved.