Axon reflex vasodilatation in cat dental pulp elicited by noxious stimulation of the gingiva

Antidromic stimulation of sensory nerves has been shown to increase blood flow in the tissue they innervate. This study was designed to determine if antidromic vasomotor responses occur in feline dental pulp and if they are mediated by branched axons supplying both tooth pulp and gingiva. Dynamic changes in pulpal blood flow (PBF) elicited by electrical stimulation, pinching, heating, and capsaicin application to the gingivae were investigated in cat mandibular canine teeth by means of Laser Doppler Velocimetry. All inferior alveolar nerve bundles and the cervical sympathetic trunk had been previously sectioned to avoid the occurrence of brainstem reflexes, e.g., somato-autonomic vasomotor reflexes. Increases in PBF were observed in seven out of 12 cats when a restricted gingival area adjacent to the canine teeth was stimulated as described, but the increases were abolished after the sensitive gingival area was painted with lidocaine jelly, a surface anesthetic. These vasodilator responses, remarkably reduced following repeated application of 30 mM of capsaicin, are considered to be induced via antidromic activation of capsaicin-sensitive nociceptive nerve fibers, presumably by axon reflex mechanisms, suggesting that nerve terminals supplying the gingiva originate from parent axons which have collaterals that innervate the canine tooth pulp.