Nitric oxide-containing structures in the carotid body and superior cervical ganglion in rats

Abstract

Introduction: The carotid body (CB) is a major peripheral chemoreceptor organ that registers the arterial blood levels of pO2, pCO2, and pH, and responds to their changes by regulating respiration. It is dually innervated by sensory fibers from petrosal ganglion (PG) neurons, and autonomic fibers from postganglionic sympathetic neu­rons of the superior cervical ganglion (SCG) and parasympathetic vasomotor fibers of intrinsic ganglion cells in the CB. Aim and Methods: The presence and distribution of nitrergic structures in the adult rat CB and SCG have been examined by means of NADPH-d histochemistry, and NOS immunohistochemistry with antibodies against its constitutive isoforms. Results: Initially, we identified the sites of origin of afferent and efferent innervation of the CB by retrograde tracing with Fast Blue, and then by combining NADPH-d staining and immunohistochemical staining for NOS we demonstrated at the light microscopic level the presence of nitrergic structures in the rat CB and SCG. Our re­sults revealed that the majority of large- and medium-sized PG and SCG cells were NADPH-d positive and dis­played a strong NOS immunostaining. We also found that the glomus cells were surrounded in a basket-like man­ner by NADPH-d reactive as well as by nNOS- and eNOS-immunoreactive varicose nerve fibers of PG and SCG or­igin. A relatively small number (4.9%) of nitrergic SCG neurons projected to both the glomus cells and blood ves­sels in the rat CB. Conclusion: The present findings provide histochemical and immunohistochemical evidence that the rat glo­mus cells receive dense sensory and autonomic nitrergic innervation while CB blood vessels are exclusively sup­plied by sympathetic and parasympathetic postganglionic NOS-containing fibers. It is likely that NO is involved in CB inhibition by way of its direct action on chemosensory glomus cells through nNOS and indirectly on its vas­culature via both nNOS and eNOS.