Immunohistochemical demonstration of tyrosine hydroxylase, serotonin and neuropeptide tyrosine in the epithelioid cells within arterial walls and carotid bodies of chicks.

By immunolight and electron microscopy, the epithelioid, granule-containing cells within the wall of circumscribed portions of the thoracic aorta, the common carotid artery, the carotid body artery and those composing the carotid body itself of newly hatched chicks were shown to contain serotonin (5-HT), neuropeptide tyrosine (NPY) and tyrosine hydroxylase (TH). No nerve fibres immunoreactive for any of these three substances were found in relation to the granule-containing cells. All the granule-containing cells were immunoreactive for 5-HT. The proportion of 5-HT cells simultaneously immunoreactive for NPY or TH in the total cell population varied in different portions of the arteries and the carotid body: NPY-immunoreactive cells were more numerous in the thoracic and common carotid arterial walls, while TH-immunoreactive cells were much more numerous in the carotid body. Since the granule-containing cells within the arterial wall, because of similarities in their anatomical features to the carotid body, are presumed to function as the arterial chemoreceptor, the difference in content of the amines and peptides among the granule-containing cells in different locations may reflect some differences in the chemoreceptive mechanism between the cells in different locations along the thoracocervical arterial tree.