Carotid bodies of amphibia (Cynops pyrrhogaster pyrrhogaster, Rana nigromaculata, Rana catesbeiana, Bufo bufo japonicus), a lizard (Eumeces latiscutatus), birds (Uroloncha domestica, Gallus domesticus) and mammals (rat, mouse, dog) including three human fetuses (6, 7 and 9 months) were studied with reference to the occurrence of monoamine-storing cells. The methods used were light microscopic chromaffin reaction after fixation in dichromate containing fluids and Falck and Hillarp's fluorescence histochemical technique.
In the amphibia, dog and human fetus, some parenchymal cells showed a positive chromaffin reaction, while in the lizard, birds, rat and mouse no chromaffin cell was recognized at all. This finding confirmed the previous descriptions of the irregular occurrence of chromaffin cells in the carotid bodies in various vertebrates.
In fluorescence microscopy of freeze-dried and formaldehyde-treated specimens, the cytoplasm of all the chief cells of the avian and mammalian carotid bodies showed green or yellow-green fluorescence. In the lizard, fluorescent cells were found singly or in small groups in the adventitia of the carotid arch where the internal carotid artery arises. In the amphibian carotid bodies cells with intense yellow fluorescence occurred within the interstitial tissue of the capillary plexus. These findings indicated the presence of monoamine-storing cells in the carotid bodies of all vertebrate species examined.
It was concluded that the absence of chromaffin reaction in the carotid body did not always mean the non-existence of monoamines in the cells, but it may imply the presence of small amounts of them. The carotid body could not be classified into non-chromaffin paraganglion on the basis of its chromaffin reaction.
Possible functional role and possible mode of the presence of monoamines in the carotid body were briefly discussed.