Characteristics of vagal afferent activity in rats: three types of pulmonary receptors responding to collapse, inflation, and deflation of the lung.

To elucidate the characteristics of vagal afferent fibers arising from rat lungs, single-unit activity from pulmonary stretch receptors and two other types of pulmonary receptors was recorded. In the latter, one type of receptor, termed deflation-sensitive receptors in this study, was stimulated only in the expiratory phase of normal respiration. Moreover, this type of receptor exhibited persistent discharges resulting in a train or burst of impulses with collapse and forced deflation, respectively. The decrease of discharge frequency during collapse was slow and the average adaptation index was 20%, indicating a slowly adapting characteristic. Upon forced deflation, the discharge frequency increased with increasing negative pressure to -158 mm H2O intratracheal pressure. The other type of receptor, termed irritant-like receptors, responded to both deflation and inflation. In addition, they displayed rapidly adapting and irregular discharges during maintained inflation. These results indicate that rat vagus nerves deliver afferent information from at least three types of pulmonary receptors: pulmonary stretch and lung irritant-like receptors and the receptors specifically sensitive to expiration or lung deflation. Furthermore, the possibility is postulated that vagal deflation-sensitive receptors are related to the peripheral mechanism in normal respiration and Hering-Breuer deflation reflex in rats.