Immunohistochemical distribution of 7B2 and colocalization with calcitonin gene-related peptide in rat lung.

The novel pituitary protein 7B2 has a widespread distribution in neurons and paraneurons and is known to be associated with endocrine disorders. In the mammalian lung, solitary neuroendocrine cells (NECs) and their innervated aggregates, termed neuroepithelial bodies (NEBs), are scattered along the bronchopulmonary tree; however, presence of 7B2 in these structures has not previously been reported. Bouin fixed, paraffin embedded rat lungs were cut and stained for 7B2, using a polyclonal antibody and a streptavidin biotin immunoperoxidase method. The identity of NEBs was confirmed on adjacent serial sections by the immunocytochemical reaction for calcitonin gene-related peptide (CGRP). NEBs selectively labelled for 7B2 are distributed throughout bronchi, bronchioli and alveolar ducts, whereas NECs are always negative. Likewise, 7B2 immunoreactivity is not detected in intrapulmonary ganglion cells nor in nerve fibers. Immunoreactivity for CGRP, on the other hand, occurs in NECs, NEBs, nerve fibers and neuronal somata. Colocalization of both peptides is demonstrated in almost all NEBs. This study presents the first immunohistochemical demonstration and morphological mapping of 7B2 in the rat lung. The finding that only NEBs are stained suggests biochemical and functional variations between NEBs and NECs as well as the absence of a role for 7B2 in the pulmonary nervous system.