Antidromic vasodilatation and neurogenic inflammation.

Antidromic stimulation of the lumbosacral dorsal roots of the rat 1.) evokes a long-lasting increase in cutaneous microcirculation of the paw as detected by the laser Doppler flowmeter, and 2.) induces plasma extravasation in the innervated skin areas and various pelvic organs. Both responses are strongly inhibited or abolished by systemic or local capsaicin desensitization. Cutaneous vasodilatation is evoked already by 1-2 pulses. Desensitization of the volar skin of the forearm abolishes the flare reaction both in the "afferent" and "efferent" side of the axon reflex. A dual sensory-efferent function for capsaicin-sensitive nociceptors is suggested. This local neuroregulatory mechanism mediates neurogenic inflammation, cutaneous vasodilatation and flare reaction not only when the receptors are activated by antidromic stimuli, but also when their orthodromic excitation by chemical means occurs.