Fine structure of the carotid body of the dog.

Since STILLING proposed in 1892 that the carotid body contains cells which become brown after treatment in potassium dichromate, the chromaffinity of the carotid body has long been a matter of dispute (for a detailed discussion, see ADAMS 1958). The occurrence of catecholamines in every glomus cell has recently been identified by pharmacological and fluorescence methods (RAHN 1961, NIEMI and OJARA 1964, BLUMCKE, RODE and NIEDORF 1967, DEARNALEY, FILLENZ and WOODS 1968), and it may be expected that all glomus cells give a positive chromaffin reaction. In spite of the widely accepted view of light microscopists that true chromaffin cells are rather uncommon and the majority of the glomus cells are negative in chromaffin reaction (WATZKA 1943, SERAFINI-FRACASSINI and FRASSON 1966), electron microscope studies (LEVER and BOYD 1957, HOFFMAN and BIRREL 1958, GARNER and DUNCAN 1958, Ross 1959, LEVER, LEWIS and BOYD 1959) have revealed that every glomus cell contains numerous membrane bound granules similar in appearance to the secretory granules of adrenal medullary cells. The first purpose of the present paper is to describe the fine structure of the glomus cells with special reference to an electron microscopically detectable difference, if any, between the chromaffin and nonchromaffin glomus cells, which seems to have been examined by none of the previous authors. Although it seems to be generally accepted that the carotid body is a chemoreceptor for the concentration of carbondioxide in the blood, there has been a vague belief among morphologists that, it, like paraganglia (KOHN 1903) elsewhere, represents a gland of internal secretion. Although an afferent innervation of the glomus is prerequisite to the chemoreceptor hypothesis, there seems to be no electron microscopic work which has clearly demonstrated an afferent terminal in this organ. Some morphologists believed that the glomus cells are of two kinds, respectively innervated by the sympathetic and parasympathetic efferent nerve fibres. Several electron microscope studies on the denervated carotid body (LEVER, LEWIS and BOYD 1958, BISCOE and STEHBENS 1867, HESS 1968, DE KOCK and DUNN 1968) indicate that most nerve endings on the glomus cells arise from the sinus nerve rather than the sympathetic nerve. Thus, the elucidation of the innervation seems to provide at least one of the keys for resolving the real function of the carotid body. The second purpose of the present paper, then, is to reexamine the nature of nerve terminals with special reference to the afferent or efferent problem and to the sympathetic or parasympathetic problem. Some new informations on the synaptic vesicles will also be given. Additional descriptions on the fine structure