Scanning electron microscopy of capsaicin-pretreated trachea in the rat during postnatal development

The morphological changes of the tracheal surface were studied in neonatally capsaicin-pretreated rats by scanning electron microscopy. One week after neonatal capsaicin treatment, a sparse number of ciliated cells were dispersed among the microvilli-covered goblet cells similar to those of the sham-operated rats. Potential ciliated cells (progenitor cells) possessed a few long cilia and many short cilia. The ciliated cells possessed cilia with a smooth surface and a blunt end similar to that of the sham-operated rats. Two weeks after neonatal capsaicin treatment, numerous ciliated cells frequently in clusters were located among large patches of microvilli-covered goblet cells similar to those of sham-operated rats. Furthermore, the blunt ends of cilia and microvilli contained short star-shaped protrusions extending into the lumen of the trachea. One month after neonatal capsaicin treatment, the star-shaped protrusions became longer, and more irregular than those of sham-operated rats. The short cilia of the potential ciliated cells (progenitor cells) also became blunt and irregular in shape. The star-shaped protrusions of the microvilli of the goblet cells became larger and thicker than those observed at two weeks following capsaicin-pretreatment. Two months after neonatal capsaicin treatment, the tracheal surface was lined with a much greater population of the ciliated cells than that at one month. A striking characteristic at this age was that globular mucin-containing secretory products were trapped within the cilia of the ciliated cells. The results of this study suggest that mucus secretion is probably blocked by the capsaicin-pretreatment. Furthermore, the star-shaped protrusions of cilia and microvilli may indicate that the mucociliary clearance mechanism is interfered with by the capsaicin-pretreatment.