Effects of postnatal age and of thymectomy on hamster pulmonary neuroendocrine system and aspects of programmed cell death.

Effects of postnatal age and neonatal thymectomy on the numbers and characteristics of pulmonary neuroepithelial bodies (NEB) were investigated in 14-day- compared with 2.5-month-old hamsters. Left lung sections were stained for the marker PGP 9.5 and used for light-microscopic quantification, while the right lungs were processed for an electron-microscopic survey of the NEB ultrastructural features. For the first time, it is clearly demonstrated that, depending on the sampling method, the number of NEB may rise or fall with age; when considering the entire lung volume, the actual number of NEB doubles, whereas when studying a constant surface area, their number apparently decreases. Also, the proportion of alveolar NEB as well as luminal contact increase on normal development. In neonates, in contrast to older animals, apoptosis is clearly present in NEB, and approximately 10% of the NEB are associated with inflammatory cells. In some cases, the dead cells have properties of both apoptosis, disintegration and cytoplasmic degeneration. The presence of intracorpuscular neutrophilic granulocytes correlates with cellular death and innervation of the NEB. Thymectomy causes only minor effects on the pulmonary neuroendocrine system. It is argued that development of the NEB and of their innervation continue during the postnatal period.