Intramural granular cells in the arteries of the carotid body region of the domestic fowl.

The major blood vessels of the carotid body region of the domestic fowl were examined with both the light and electron microscope. With the light microscope, argyrophilic cells were found in the wall of the common carotid artery, carotid body artery, oesophagotracheobronchial artery, and the common trunk for the latter two arteries. With the electron microscope, cells containing granular vesicles were found in all the above mentioned arteries. In the wall of the common carotid artery two types of granular cell were found, one with small granular vesicles (60-140 nm) and the other with large granular vesicles (100-300 nm). Capillaries were not present amongst these cells, apposed axonal endings were infrequently seen, and there were no synapses. It is concluded that these cells do not have a chemoreceptor function but may secrete amines or peptides with a local action. Since the cells are located in the baroreceptor zone of the common carotid artery their secretions may modulate baroreceptor activity. In the other three arterial sites and on the distal vagal ganglion there were groups of granular cells characterised by small (60-140 nm) granular vesicles. These granular cells, together with their associated fenestrated capillaries, apposed axonal endings with synapses, and cells resembling carotid body Type II cells were interpreted as aberrant carotid body tissue, presumably with a chemoreceptor function.