The role of Substance P in the axon reflex in the rat

Abstract

The increase in vascular permeability in small blood vessels of rat skin induced by antidromic stimulation of sensory roots, nerves, or single identified polymodal nociceptive fibers or by intra-arterial injection of substance P [SP] was examined by light microscopy and EM. The effects of local application of capsaicin (a SP-depleting agent) to both skin and muscle were also studied. Nerve-stimulation and SP induce leakage of a venular pattern similar to that caused by known permeability factors. Capasaicin causes leakage from both venules and capillaries in a pattern more characteristic of direct endothelial injury. Neurogenic leakage may be mediated by local liberation of SP, but caution is necessary in interpreting experiments involving the use of capsaicin because of its local toxic effects.