MECHANISMS OF ALLODYNIA - INTERACTIONS BETWEEN SENSITIVE MECHANORECEPTORS AND NOCICEPTORS

WE examined whether stimulation of sensitive mechanoreceptors from an area of allodynia evokes nociceptor activity expressed as axon reflexe s. Experiments were conducted on human volunteers. Cutaneous blood flo w was measured with a laser Doppler flowmeter. Allodynia was induced w ith mustard oil (25-100%) or by intradermal injections of capsaicin (2 5-50 mu g) in the skin of the forearm or the hand. Tactile stimulation of normal skin or outside zones of allodynia did not evoke axon refle xes. The same stimulation in areas of allodynia evoked pain as well as axon reflexes. Cooling the area of primary hyperalgesia or blocking t he A fibres in the nerve that innervated the allodynia area abolished the allodynia and the axon reflex. These results demonstrate central i nteractions between sensitive mechanoreceptors and nociceptors concomi tant with the development of allodynia.