Fifty years of progress in carotid body physiology--invited article.

Research on arterial chemoreceptors, particularly on the carotid body, has been fruitful in the last fifty years, to which this review is addressed. The functional anatomy of the organ appears to be well established. The biophysical bases by which glomus cells transduce chemical changes in the milieu intérieur (hypoxia, hypercapnia, acidosis) into electrical and biochemical changes in glomus cells have received much attention. Physical changes (in temperature, flow and osmolarity) are also detected by the carotid body. Electrical coupling between glomus cells themselves appears as very extensive. Sustentacular cells classically considered as ensheathing glia for glomus cells and nerve endings now appear to behave as stem cells precursors for glomus cells under chronic hypoxic conditions. Many papers have been devoted to transmitters released from glomus cells (acetylcholine, dopamine, ATP) and well as to their effects upon chemosensory nerve activity. Chemosensory neurons have been explored from generation of action potentials at peripheral nerve endings, passing to properties of perikarya at petrosal ganglia and finally at characterization of synaptic transmission at solitary tract nuclei. There is abundant literature on ventilatory and cardiovascular reflexes elicited from arterial chemoreceptors. The transient effects of sudden and brief withdrawal of chemosensory discharges by hyperoxia also provide clues on the role played by carotid bodies in the homeostasis of full organisms.