Neuroendocrine cells of the lung, occurring singly or in clusters known as neuroepithelial bodies, contain a variety of biologically active compounds, including several neuropeptides. We have investigated the localization of calcitonin and calcitonin gene-related peptide (CGRP) within single and grouped neuroendocrine cells in the respiratory epithelium of rats by an immunohistochemical double-staining technique which uses specific antisera raised in heterogeneous animal species. Calcitonin- and CGRP-immunoreactivities were nearly totally co-localized in both single neuroendocrine cells and neuroepithelial bodies. CGRP-immunoreactivity was also present in neurons in the jugular, nodose and dorsal root ganglia. The calcitonin-immunoreactivity in neuroendocrine cells, as in thyroid parafollicular (C) cells, was abolished by preincubation of the anticalcitonin serum with synthetic calcitonin. The CGRP-immunoreactivity in neuroendocrine cells and in the neuronal cells was abolished by preincubation of anti-CGRP serum with synthetic CGRP. Thus, while the calcitonin gene is expressed exclusively or predominantly as either calcitonin or CGRP in all other tissues except thyroid C-cells, our results strongly suggest that both peptides are expressed in the rat bronchopulmonary neuroendocrine cells.
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