INTERACTIONS BETWEEN SYMPATHETIC VASOCONSTRICTOR OUTFLOW AND C-NOCICEPTOR-INDUCED ANTIDROMIC VASODILATATION

The interaction between orthodromic sympathetic vasoconstrictor and an tidromic vasodilator effects of C-fiber stimulation was studied in nor mal human volunteers. Excitation of C fibers was achieved through admi nistration of intermittent painful intraneural microstimulation to upp er limb nerves, while recording cutaneous thermal emission profiles in the projected fields of cutaneous sensation. During initial stimulati on, when both systems are co-activated, skin temperature decreased. Te mperature increased after termination of the stimulus. Eventually, tem perature decreased again upon renewed stimulation. Thus, sympathetic v asoconstriction was found to override the antidromic vasodilator effec t induced by stimulation of C nociceptors. When interpreting abnormal deviations of skin temperature in patients with peripheral nerve disor ders, the dynamic interplay between opposing vasomotor effects driven by sympathetic and somatic systems must be taken into consideration.