Blood flow increases in the skin of the anaesthetized rat that follow antidromic sensory nerve stimulation and strong mechanical stimulation.

In anaesthetized rats, punctate pressure using forces greater than or equal to 20 mN caused small transient rises in skin blood flow that were similar in normally innervated and chronically denervated skin. A force of 11 mN, sufficient to excite most C-fibres of the polymodal nociceptor class, failed to cause vasodilatation. Following short periods of low frequency electrical stimulation of the saphenous nerve at C-fibre strength, larger increases in blood flow ('antidromic vasodilatation') were seen. Antidromic vasodilation was unaffected by high frequency stimulation of A alpha beta axons or by simultaneous innocuous mechanical stimulation. The failure of pressure at levels suprathreshold for C-fibre nociceptors to cause neurogenic vasodilatation may mean that antidromic vasodilation in rat skin is due to activity restricted to a mechanically insensitive sub-population of C-fibres.