Carotid-body-like tissue within the recurrent laryngeal nerve: an endoneural chemosensitive micro-organ?

Paraganglia associated with the ninth and tenth cranial nerves have been observed in several locations in the head and neck region. The most studied of these organs, both morphologically and functionally, is the carotid body, a chemoreceptor organ located in the carotid bifurcation. In the present study a microglomus (microparaganglion) composed of islands of carotid-body-like cells was found in the endoneural space of the recurrent laryngeal nerve of rats, 5 to 10 mm from the nerve entrance into the larynx. This microglomus was surrounded by bundles of myelinated and unmyelinated nerve fibers. Fenestrated blood vessels were observed between cells. The cells were characterized by their cytoplasmic membrane-bound granules and dense-core vesicles. Ultrastructurally, these cells seemed to be identical to carotid body chemoreceptor cells and thus to indicate that the cells of the microglomus store catecholamines. Nerve terminals impinging on the cells, classified as both afferent and efferent, were also identified. The recurrent laryngeal endoneural microglomus may have a chemosensitive function influencing the laryngeal physiologic reflex mechanisms.