Nitric oxide synthase expression in the medullary respiratory related nuclei and its involvement in CO-mediated central respiratory effects in neonatal rats

The present study was conducted in order to observe the potential participation of the nitric oxide synthase–NO pathway in CO-mediated regulation of respiration of neonatal rats. An immunofluorescent histochemical technique was used to examine the existence of the neuronal nitric oxide synthase, a key enzyme of synthesizing NO, in medullary respiratory nuclei. The rhythmic respiratory-like discharges of hypoglossal rootlets of medullary slices were recorded to test the role of the nitric oxide synthase in CO-mediated respiratory effects. We observed neuronal nitric oxide synthase expressed in the medullary respiratory nuclei in conjunction with CO lengthened expiratory duration, decreased respiratory frequency, and increased inspiratory amplitude. These CO-mediated respiratory effects could be partially eliminated by prior treatment of the slices with Nω-nitro-l-arginine methyl ester, an inhibitor of nitric oxide synthase. The results suggest that nitric oxide synthase–NO pathway might be involved in the CO-mediated central regulation of respiration at the level of medulla oblongata in neonatal rats.