Innervation of rabbit fetal lungs

Nerve fibers, autonomic ganglia, and neuroepithelial bodies of the lungs of rabbit fetuses, 17 to 31 days gestational age, were studied with neurohistological techniques including silver impregnation, acetylcholinesterase histochemistry, and glyoxylic-acid-induced histofluorescence for monoamines. The silver impregnation method showed that nerve fibers and ganglia accompanied the bronchi and large pulmonary blood vessels to enter the developing lungs by the 17th day of gestation. Cholinergic and adrenergic nerves began to appear in the walls of the bronchi on the 21st day. The developing pulmonary arteries had accompanying adrenergic nerves on the 25th day. Acetylcholinesterase-positive parasympathetic ganglia were seen on the 27th day. Silver-impregnated nerve fibers in the developing alveolar walls and pleura were found on the 25th day. Neuroepithelial bodies and specialized single cells which were argyrophilic, acetylcholinesterase-positive, and fluorescent could be demonstrated in 19--21-day-old and older fetuses; and some of these structures were innervated by sensory and autonomic motor fibers. These observations indicated that nervous tissue and neuroepithelial bodies appeared in the lungs during the glandular stage of the lung development and that differentiation of adrenergic and cholinergic nerves began in the late glandular stage.