Distribution of capsaicin-sensitive nerve fibres containing immunoreactive substance P in cutaneous and visceral tissues of the rat.

Treatment of newborn rats with capsaicin causes a selective and permanent degeneration of unmyelinated sensory fibres, some of which contain immunoreactive substance P (ISP). Following treatment of newborn rats with capsaicin (50 mg/kg), the ISP content was decreased by 66-75% in various skin areas and in the oral and nasal mucosae as measured at the age of 3-4 months. There was no significant depletion of ISP in the mucosa of the tongue. The ISP content of trachea, lungs, myocardium, hepatic duct, ureter and urinary bladder, was decreased by 60-84%. The ISP concentrations in stellate and mesenteric ganglia were reduced by 54 and 81%, respectively. These results indicate a widespread innervation of cutaneous and visceral tissues by sensory nerve fibers containing ISP.