A Confocal Microscopic Study of the Formation of Ganglia in the Airways of Fetal Pig Lung

Fetal airway smooth muscle contracts to neural stimulation from early gestation. This study aimed to document the development of the nerves and ganglia within the bronchial tree of the fetal pig lung as the structural correlates for this function. The formation of these structures during lung development (pseudoglandular stage, canalicular stage, and saccular stage) was followed through to the postnatal period, using antibodies to protein gene product 9.5, a nonspecific nerve marker; synaptic vesicle protein 2, a marker of synaptic vesicle membranes; and neurofilament, a marker of filaments in the neuronal cytoskeleton. Glial cells were stained for glial fibrillary acidic protein (GFAP) and S-100, and the airway smooth muscle for a-actin. Whole mounts of the bronchial tree were imaged using confocal microscopy. The formation of ganglia commences in the pseudoglandular stage with patches of neuroblasts in the wall of the epithelial tubules. These ganglionic precursors are supplied with an abundance of nerve trunks and fibers that arise from the vagus and extend to the growing tips of the airways. These trunks show profiles of Schwann cells. As the airways grow, the ganglionic precursors condense at the nerve junctions. Nerve bundles in trunks and neurons in ganglia become increasingly enveloped by GFAP-positive sheaths. From midterm onward (canalicular stage), ganglia contain cholinergic neurons. In the third trimester (saccular stage) and postnatally, ganglia further increase in size and contain mainly nerve fibers in the center. Thus, neural tissue is a dominant feature of the primordial lung, which is enveloped by nerves and ganglia through gestation into postnatal life.