Cholinergic nerves in the parietal pleura

Identification and properties of parietal pleural afferents in rabbits

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 degrees 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 cmH2O) 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.

Nerve fibers--mast cells correlation in the rat parietal pleura

Our results show that a morphological correlation exists between catecholaminergic nerve fibers and mast cells in the rat parietal pleura. Mast cells are found in proximity to catecholaminergic nerve fibers. Moreover we have demonstrated that mast cells and nerve fibers in the perivascular areas of rat parietal pleura show the same formaldehyde fluorescence. In rats previously sympathectomized with neurotoxin 6-OHDA the nerve fibers appear disarranged and poorly fluorescent and related mast cells show a low fluorescence. The importance of this correlation and the possible role of mast cells are discussed.