Identification and properties of parietal pleural afferents in rabbits

Abstract

Although pain and dyspnoea are common symptoms in pleural diseases, there are few studies on the sensory innervation of the pleura. Using rabbits, after removal of all muscles in the intercostal space to be studied, we investigated the afferents of the internal intercostal nerve by applying to the internal thoracic wall pieces of gauze soaked in warmed (37 • C), buffered saline (mechanical stimulation) or solutions containing lactic acid, inflammatory mediators or capsaicin (chemical stimulation). The afferent conduction velocity ranged from 0.5 to 14 m s −1 . Most units (97%) were activated by mechanical stimulation of the pleura (local positive pressure range = 4.5-8.5 cmH 2 O) and we found a linear relationship between the discharge rate of afferents and the force applied to the thoracic wall. The majority of mechanosensitive units (70%) also responded to one or several chemical agents. Thus, the afferents were activated by lactic acid (49%) and/or a mixture of inflammatory mediators (50%). Local application of capsaicin elicited an initial increased or decreased background afferent activity in 57% of the afferents, a delayed decrease in firing rate being noted in some units initially activated by capsaicin. Capsaicin blocked the afferent response to a further application of inflammatory mediators but did not affect the mechanosensitive units. Thus, sensory endings connected with thin myelinated and unmyelinated fibres in the internal intercostal nerve detect the mechanical and chemical events of pleural diseases.

Is TRPV1 a useful target in respiratory diseases?

“…Recently, parietal pleura afferents were found in the intercostal nerves of rabbits, and these myelinated and unmyelinated fibers had multi-modal properties [40]. In addition, a very recent study demonstrated the presence of acid-sensitive channels, TRPV1 and acid sensing ion channel-3 (ASIC3) in rat DRG neurons projecting to the pleura.…”

Respiratory and circulatory effects of parietal pleural afferent stimulation in rabbits

“…The composition of this mixture was the same as in our previous study (19) and also that by Wedekind (36). The contact of the pleura with the inflammatory mixture solution was maintained for a 30-s period.…”

“…We concluded that an acute mechanical distension of the parietal pleura as well as its chemical stimulation by lactic acid elicit a marked inhibition of phrenic motoneurons combined to a reduction of the sympathetic outflow to the circulatory system. pleura; sensory innervation; phrenic activity; circulatory control IN A PREVIOUS STUDY IN RABBITS, we identified afferents in internal intercostal nerves that were activated by mechanical and/or chemical stimulation of the thoracic pleura (19). The nerve responses were attributed to the selective activation of pleural afferents because they existed after complete removal of all muscles covering the studied intercostal spaces.…”

“…On the basis of our previous data of the behavior of pleural afferents in internal intercostal nerves (19), we conducted an experimental study in the same species to explore the consequences of mechanical or chemical stimuli applied to the parietal pleura on the breathing pattern (phrenic discharge) and the circulatory function (blood pressure, heart rate). Some data exist in the literature on the respiratory effects of internal intercostal nerve stimulation, but they are only based on electrical stimulation of the whole nerve trunk or mechanical activation of nerve endings, but not on their chemical activation.…”

Effect of histamine on the electrophysiology of the human parietal pleura

“…Furthermore, commonly used anti-histaminic agents can suppress this effect, a fact which, although at experimental level, may provide new treatment options for exudation or other histamine-mediated adverse effects throughout the body (Tepetes et al 2009). Finally, it has been suggested that histamine and other inflammatory mediators stimulate sensitive nerve endings positioned on the mesothelial surface of the parietal pleura which participate in respiratory and circulatory control (Jammes et al 2005, Jammes andDelpierre, 2006).…”