Cholinergic nerve development in fetal lung

Cholinergic nerve development in rat fetal lung can be monitored effectively using acetylcholine esterase histochemical staining techniques on frozen sections. Neuroblasts were detected first by these techniques on fetal Day 13 in the indifferent mesenchyme surrounding the trachea. Subsequently, they migrated to the level of the third tracheal branch and matured progressively to ganglia. Neither nerve fibers, ganglia, nor nerve endings of cholinergic variety were detected further in the periphery of the lung. Neuroepithelial cells with lightly staining cytoplasmic acetylcholine esterase-positive granules were first seen on Day 17, after which they were found along the epithelial lining of the entire tracheobronchial tree. These epithelial cells may be potential intrapulmonary chemoreceptors.