FUNCTIONAL EVIDENCE FOR THE DIFFERENTIAL CONTROL OF SUPERFICIAL AND DEEP BLOOD-VESSELS BY SYMPATHETIC VASOCONSTRICTOR AND PRIMARY AFFERENT VASODILATOR FIBERS IN RAT HAIRLESS SKIN

We quantitatively investigated sympathetic vasoconstriction and antidr omic vasodilation mediated by small-diameter primary afferents on the plantar hairless skin of the hindpaws in Wistar rats using laser Doppl er (LD) flowmetry and an infrared thermometer. Sympathetic vasoconstri ction was elicited by electrical stimulation of the centrally cut ipsi lateral lumbar sympathetic trunk (LST) with 50-s trains at 0.1-20 Hz. Antidromic vasodilation was evoked by electrical stimulation of the do rsal 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 resu lted 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. W hen 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 degree s C), DR stimulation still resulted in large increases in LD flow, but only minor changes in SKT. These results suggest that blood flow thro ugh both deep and superficial layers of rat hairless skin is regulated by activity in sympathetic postganglionic vasoconstrictor fibres, whe reas small-diameter primary afferent fibres appear to influence predom inantly the blood flow through superficial layers of rat plantar skin.