Ultrastructural analysis of the mouse nasal septum. Respiratory cilia prior to an after birth. A quantitative freeze-fracture study.

Respiratory cilia of mice from 3 days prior to birth till 21 days after birth were examined by freeze-fracture preparations for the determination of the frequency and size of the intramembranous particles (IMPs). Dependent on the age of the animals different numbers and sizes of IMPs were found. A significant drop in total number of IMPs in all diameter classes was most evident from the 19th day of gestation to the 20th day (1 day prior to birth), followed by a marked rise between embryonal day 20 and the 1st postnatal day. The results were discussed with regard to morphological and functional changes in the respiratory system prior to and after birth.