Functional evidence for the differential control of superficial and deep blood vessels by sympathetic vasoconstrictor and primary afferent vasodilator fibres in rat hairless skin.

We quantitatively investigated sympathetic vasoconstriction and antidromic vasodilation mediated by small-diameter primary afferents on the plantar hairless skin of the hindpaws in Wistar rats using laser Doppler (LD) flowmetry and an infrared thermometer. Sympathetic vasoconstriction was elicited by electrical stimulation of the centrally cut ipsilateral lumbar sympathetic trunk (LST) with 50-s trains at 0.1-20 Hz. Antidromic vasodilation was evoked by electrical stimulation of the dorsal root (DR) L5 with 20-s or 50-s trains at 1-4 Hz. Cutting the LST resulted in increases in skin temperature (SKT) by 6.1 +/- 1.0 degrees C (mean +/- SEM) and in LD flow by 128 +/- 20%. Stimulation of the LST resulted in a graded decrease in LD flow and SKT that was most pronounced between 0 and 0.1 Hz. However, DR stimulation evoked a large increase in LD flow but only little change in SKT in rats with sectioned LST. When the DR was stimulated either in animals with intact LST or during continuous stimulation of vasoconstrictor fibres in the sectioned LST, i.e. while baseline temperature was relatively low (26.3 +/- 1.1 degrees C), DR stimulation still resulted in large increases in LD flow, but only minor changes in SKT. These results suggest that blood flow through both deep and superficial layers of rat hairless skin is regulated by activity in sympathetic postganglionic vasoconstrictor fibres, whereas small-diameter primary afferent fibres appear to influence predominantly the blood flow through superficial layers of rat plantar skin.