Central and reflex regulation of sympathetic vasoconstrictor activity to limb muscles during desynchronized sleep in the cat.

Desynchronized sleep (DS) in the cat is accompanied by a long-lasting (tonic) constriction of muscle blood vessels (conductance decrease 5-30%), on which are superimposed short-lasting (phasic) vasoconstrictor waves that occur simultaneously with bursts of rapid eye movements and body twitches. Both the tonic and the phasic vasoconstrictions are abolished after regional sympathectomy (conductance increase 5-10%). Tonic vasoconstriction can also be prevented by hind-limb deafferentation (bilateral section of the dorsal roots from L5 down) or by transection of the spinal cord at L4 in such a way as to separate sympathetic innervation from afferent input from the hind limbs. These procedures do not affect the phasic vasoconstrictions. After lumbar sympathectomy or hind-limb deafferentation, iliac blood flow decreases during the tonic fall in blood pressure associated with DS by exactly the amount (1-2 ml/min) predicted by pressureflow relationships observed during artificial lowering of iliac blood pressure. We conclude that tonic and phasic vasoconstrictions are both due to sympathetic discharges. However, phasic sympathetic discharges are driven by central descending influences, and tonic sympathetic vasoconstriction depends on reflex influences originating from the limbs themselves. When tonic sympathetic vasoconstriction is prevented, muscle blood vessels exhibit autoregulatory behavior during DS.