The Search of Vagal Pulmonary Pleural Innervation

The visceral pleura envelops the lung lobes. The visceral and parietal pleurae form the pleural cavity with negative pressure to keep the normal respiration possible. The lungs are complicatedly innervated by bilateral vagal and spinal nerves that have the sensory and motor components. Pulmonary vagal sensory receptors have been identified within the tissues in the extrapulmonary and intrapulmonary airways. However, vagal vs. spinal innervation in the pulmonary visceral pleura has been undecided. Mollgaard (1912) determined the neurons that innervate the lungs by whole or partial extirpation of the lung lobe. Larsell (1922) examined the vagal degeneration in the lungs and supported the vagal origin. However, Larsell and Coffey (1928) turned to the spinal origin when they inserted the balloon between the lung lobe and the chest wall or diaphragm and found no change in the rate and depth of inspiration. With vagotomy and excision of the second and third thoracic spinal ganglia, Honjin (1956) determined the vagal and rejected the spinal origin. With vagotomy, Pintelon and colleague (2007) identified non-vagal ＂visceral pleura receptors＂. Recently, we identified the classical hilar and novel non-hilar vagal pleural innervation pathways and two kinds of vagal nerve endings in the visceral pleura and triangular ligaments. Most of the areas that face the dorsal thoracic cavity have no vagal innervation, whereas the interlobar areas and those areas that face the heart receive bilateral or unilateral vagal innervation with a left-vagus-rostral-lung vs. right-vagus-caudal-lung lateralized innervation pattern. The experimental considerations and meanings for the vagal innervation pattern are discussed.