ONTOGENY OF ENDOCRINE-CELLS IN THE RESPIRATORY SYSTEM OF SYRIAN GOLDEN-HAMSTERS .1. LARYNX AND TRACHEA

The ontogeny of protein gene product 9.5 (PGP 9.5), serotonin (5-HT), calcitonin gene-related peptide (CGRP), and calcitonin (CT) immunoreac tivity was evaluated in small-granule endocrine cells of hamster laryn gotracheal epithelium from fetal day 11 to adulthood. Two centrifugal (proximal-to-distal) patterns of differentiation occur. The first patt ern begins during fetal life. Endocrine cells, single and clustered in groups (presumptive- or protoneuroepithelial bodies, pNEBs), initiall y colocalize immunostaining for PGP 9.5, 5-HT, and CGRP in the larynx and proximal 2/3 of the trachea on day 12 and spread to the caudal tra chea on day 13.5-HT disappears fleetingly during the 24 h preceding bi rth; otherwise immunoreactivity for all three substances persists into adulthood. The clusters of endocrine cells survive beyond birth but a re so diluted by expansion of the nonendocrine epithelium as to become inconspicuous. Since innervation was not actually observed, these clu sters may persist as pNEBs, without developing connections to afferent or efferent nerve fibers. The second pattern concerns single small-gr anule cells stainable for CGRP but not for 5-HT. These cells first app ear in the larynx and cartilaginous part of the cranial trachea on pos tnatal day 3, and in the middle and caudal trachea, on day 5. The cell s increase in number on day 7. In adults, they predominate among endoc rine cells of the cartilaginous region. A subset of these cells begins to co-express CT proximally on postnatal day 10, reaching the caudal end of the trachea by 3 weeks. A few elements of the older 5-HT-positi ve population may also become immunoreactive for CT in juvenile hamste rs.