Hyperoxia, during development in rats, results in hypoxic chemosensitivity ablation, carotid body hypoplasia, and reduced chemoafferents. We hypothesized that hyperoxia increases reactive oxygen species (ROS) in cell bodies of chemoafferents. Organotypic slices of petrosal-nodose ganglia from rats at day of life (DOL) 5-6 and 17-18 were exposed to 8%, 21%, or 95% O 2 for 4 h in the presence or absence of the ROS-sensitive fluorescent indicator, CM-H 2 DCFDA, and propidium iodide was used to determine the relationship between cell death and oxygen tension. In tissue slices from DOL 5-6 rats, fluorescence intensity was 182.5 Ϯ 2.9 for hypoxia, 217.5 Ϯ 3.3 for normoxia, and 336.6 Ϯ 3.8 for hyperoxia, (mean Ϯ SEM, p Ͻ 0.001, ANOVA). Normoxia increased ROS levels by 19.2% from hypoxia (p Ͻ 0.01) with a further increase of 54.8% from normoxia to hyperoxia (p Ͻ 0.001). In tissue slices from DOL 17-18 rats, ROS levels increased with increasing oxygen tension but were less than in younger animals (p Ͻ 0.01, ANOVA). The antioxidants, NAC and TEMPO-9-AC, attenuated ROS levels and cell death. Electron microscopy demonstrated that hyperoxia damages the ultrastructure within petrosal ganglion neurons. Hyperoxic-induced increased levels of ROS in petrosal ganglion neurons may contribute to loss of hypoxic chemosensitivity during early postnatal development. N umerous studies in mammalian species support a role for peripheral arterial chemoreceptors in stabilizing ventilation at a critical period during early postnatal development, which establishes rhythmogenesis that is sustained throughout life (1,2). The components of the peripheral arterial chemoreceptors are found within the carotid body that is located in the bifurcation of the carotid artery and consists of three major neuronal components that include: 1) type I chemosensory cells, also known as glomus cells, which contain neurotransmitters and autoreceptors; 2) type II cells, which are similar to supportive glial cells; and 3) chemoafferent nerve fibers from the carotid sinus nerve, a branch of the IX cranial nerve, with cell bodies in the petrosal ganglion (PG) (3,4).Exposure to chronic hyperoxia, during the first weeks of postnatal development, depresses ventilatory responses to subsequent acute hypoxia in newborn animals and in premature infants (5-7). Hyperoxic exposure in newborn rat pups is cytotoxic to peripheral arterial chemoreceptors as evidenced by hypoplasia of the carotid body and a 41% reduction in the number of chemoafferent neurons (8). The mechanisms leading to cytotoxic changes in the carotid body and the reduction in chemoreflexes after hyperoxicexposure during early postnatal development are unknown. In other model systems, hyperoxia is associated with increased production of ROS, including superoxide, hydroxyl radical, and hydrogen peroxide, which can contribute to cellular damage via lipid peroxidation, enzyme inactivation, and protein and nucleic acid oxidation, resulting in apoptosis or necrosis (9). Using a novel ex vivo organotypic s...
