Role of tachykinins in neurogenic inflammation

Recent observations on the distribution, release, and biologic properties of neuropeptides connected to sensory neurons have added new information about the mechanism of hyperemia, plasma extravasation, and increase in smooth muscle tone induced by sensory nerve stimulation and by mechanical, physical, or chemical stimuli. To date, Substance P (SP) is the best characterized of these peptides. Using the skin, eye, and respiratory tract as experimental models, it has been shown that: 1) SP is widely distributed in primary sensory neurons as well as in afferent sensory fibers in the vagus, 2) SP is released from sensory nerve terminals during antidromic stimulation, 3) local administration of SP mimics the effect of sensory nerve stimulation, and 4) hyperemia, plasma leakage, and smooth muscle contractions, normally induced by nerve stimulation or noxious stimuli, are absent in tissues pretreated with the SP depleting agent capsaicin or with SP antagonists. These findings indicate that peptidergic nerve fibers are involved in the local regulation of blood flow, vascular permeability, and the tone of smooth muscles. In addition, they give new insights in the pathophysiology of hyperreactive disorders and neurogenic inflammation.