Unilateral cervical vagotomy decreases the magnitude of neurogenic inflammation induced by capsaicin in the ipsilateral bronchial tree of rats.

Abstract

Electrical stimulation of a single cervical vagus nerve produces neurogenic inflammation on the stimulated side of the bronchial tree, including the first (main) to the 4th order bronchi. In the contralateral bronchial tree, in contrast, only the proximal part of the main bronchus exhibits inflammatory changes, suggesting that vagal sensory axons present in the bronchi largely originate from the ipsilateral vagus nerve. Intravenous administration of capsaicin can evoke neurogenic inflammation in bilateral bronchial trees. Sensory axons from various sources are thought to be stimulated by this irritant. The extent to which neurogenic inflammation in both bronchial trees might be reduced by unilateral vagotomy is not known. In the present study, we sought to characterize the effect of unilateral cervical vagotomy on capsaicin-induced changes in plasma extravasation and secretory activity of goblet cells in the bronchial trees of both sides. To quantify the magnitude of neurogenic plasma extravasation, Evans blue was used as a tracer dye to measure spectrophotometrically its amount in the bronchial wall. Another tracer dye, Monastral blue, was used to localize the distribution of leaky blood vessels and to measure morphometrically their area density in the whole mounts. To investigate cell and tissue responses of the mucosa, histological methods were employed. After 2 or 4 postoperative weeks, the rats were intravenously administered with a single dose of capsaicin, 150 μg/kg. This resulted in different magnitudes of Evans blue extravasation in the bronchi of the two sides in vagotomized rats. Extravasation of Evans blue dye in the bronchial tree ipsilateral to vagotomy was one-half to two-thirds of that of the contralateral bronchial tree. For the distal region of the main stem bronchus, the area density of Monastral blue-labeled blood vessels in the operated side was one-half of that in the unoperated side, and for the secondary bronchus, the area density of these blood vessels in the operated side was one-quarter of that in the unoperated side. Histological study indicated that in the bronchial mucosa ipsilateral to vagotomy edematous change was not obvious, and most goblet cells were not responsive to stimulation by capsaicin, in contrast to the contralateral side where edematous change was very prominent and goblet cells were very sensitive to capsaicin. It is concluded that unilateral cervical vagotomy could selectively desensitize the mucosa of the ipsilateral bronchial tree to capsaicin, and therefore, decrease the magnitude of neurogenic inflammation.