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

Abstract

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 capsaicinpretreatment. 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.