Norepinephrine-containing glomus cells in the rabbit carotid body. II. Immunocytochemical evidence of dopamine-beta-hydroxylase and norepinephrine.

The presence of noradrenergic glomus cells in the rabbit carotid body was investigated at the light and electron microscope levels, using dopamine-beta-hydroxylase and norepinephrine immunocytochemistry as well as the chromaffin reaction. Frozen and semi-thin plastic sections showed some dopamine-beta-hydroxylase immunoreactive glomus cells either isolated in the connective tissue or, more frequently, mixed with unreactive cells. At the ultrastructural level immunopositive cells differed from immunonegative ones by the larger size of most of their dense-cored vesicles. Similar observations were made after using anti-norepinephrine antibodies. Immunoreactive cells to anti-dopamine-beta-hydroxylase and anti-norepinephrine antibodies were relatively few although their number varied from carotid body to carotid body. The immunolabelling intensity was very variable from cell to cell. Consecutive frozen sections processed for norepinephrine- and dopamine-immunocytochemistry showed many cell clusters containing both norepinephrine and dopamine-immunoreactive glomus cells. Some chromaffin glomus cells were clearly identifiable by the very strong electron opacity of their dense-cored vesicles; most of these vesicles were characterized by their large size, as the dense-cored vesicles observed in dopamine-beta-hydroxylase- and norepinephrine-immunopositive cells. These results demonstrated that dopamine-beta-hydroxylase and norepinephrine-immunopositive, as well as chromaffin cells, were identical to the cells which take up exogenous norepinephrine, described in part I of this study. However, many intermediate levels were found between norepinephrine-immunonegative and strongly norepinephrine-immunopositive glomus cells, suggesting that the distinction between these two kinds of cells is not clearcut.