Abstract: Objective To study the effect of histamine in rat ventrolateral preoptic area on sleep-wakeful?ness cycle. Methods Histamine was microinjected into ventrolateral preoptic area through stereotaxic technique，sleeping and waking time phases were recorded and analyzed by electroencephalograph.Results Microinjection of 50 μmol/L histamine had no significant effect，but 100 μmol/L histamine decreased sleeping time and increased waking time significantly. Conclusion Histamine is involved in regulation of sleep-waking cycle and promotes wakefulness significantly in the ventrolateral preoptic area.

Key words: histamine, ventrolateral preoptic area, sleep-wakefulness cycle