[Pain reception in the skin studied with chemical agents]

Cutaneous C-fibre polymodal mechano-heat (CMH) sensory units of narcotized cats have been studied for their responses to the close-arterial injection of potassium, acetylcholine and methacholine to the saphenous artery in subnoxious and noxious concentrations. Subnoxious chemical stimulation has induced low-frequency excitation of CMH units. The parameters of CMH units firing during subnoxious and noxious chemical stimulation may be used for estimation of effects of local anesthetics. To achieve local anesthesia it is sufficient to inhibit only high frequency responses in CMH units without a complete block of these sensors. With that end in view the use-dependent blockers of nerve excitation are suggested. The use-dependent inhibition of CMH units was found during mechanical stimulation under the action of lidocaine or n-propylajmaline. The mathematical model of C-fibre has demonstrated the key role of slow changes of membrane ionic permeabilities in determining the firing rate elicited by chemical stimulation.