Anatomic and Functional Sites of Receptor Location

Autoradiographic studies of human and guinea-pig airways have demonstrated the presence of tachykinin receptors on vascular smooth muscle, airway epithelium and submucosal glands, with a particularly hi density on airway smooth muscle from the trachea to small bronchioles (Castairs and Barnes, 1986 Hoover and Hancock, 1987). In contrast, in rat airways, there is no labelling of airway smooth muscle (Sertl et al., 1988). 

Adcock et al. (1993) reported increased levels of Nkl receptor mRNA in airway tissue obtained from asthmatic subjects compared to normal subjects. However, these authors did not evaluate the cellular distribution of receptor protein. In contrast, Bai et al. (1994) reported no difference between levels of Nkl receptor mRNA in lung tissue from non-asthmatic subjects and that in lung tissue from asthmatic patients these investigators did find that the level of Nk2 receptor mRNA was increased in the asthmatic individuals. The medications used for the treatment of asthma may explain this discrepancy Adcock et al. (1993) have shown that treatment with glucocorticoids decreases Nkl receptor expression in asthmatic airways. 

Histologic evidence shows a close anatomic correspondence between mast cells and G-fibers in peripheral organs (Skofitsch et al., 1985 Stead et al., 1987) and in the nodose ganglia (Undem and Weinrich, 1993). There is both functional and structural evidence for innervation of mast cells by C-fibers. Stimulation of the trigeminal nerve causes mast cells in the rat dura mater to degranu-late. This effect, which is apparent on histologic evaluation, is abolished by treatment with neonatal capsaicin and this may be mediated by C-fibers (Dimitriadou etal., 1991). 

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