Vasomotor adjustments in the rabbit's ear during REM sleep

In the rabbit auricolar vessels constrict during REM sleep at high ambient temperatures (26-30 degrees C) and dilate a low ambient temperatures (0-5 degrees C). These opposite vasomotor adjustments during REM sleep are inconsistent with the logic of a thermoregulatory mechanism; they can only be understood as new equilibria of the vessels calibre to the drop in sympathetic vasoconstrictor tone and fall in transmural pressure during REM sleep. By cutting the sympathetic nerve supply to the ear we can rule out the neurogenic origin of ear vasoconstriction during REM sleep.