Objective　To investigate the effect of extragenous adenosine (AD) by microinjection in the orexinergic area of rat lateral hypothalamus (LH) on the sleep-wake cycle. 　Methods　A total of 14 male SD rats were given 1

10 or 20 nmol AD and artificial cerebrospinal fluid (aCSF) as own control through three different models of microinjections into the LH. Their electroencephalogram (EEG) and electromyogram (EMG) were recorded by a polygraph recording instrument to observe the changes of sleep-wake after microinjections. 　Results　AD administration to LH at doses of 1

10 and 20 nmol decreased the total amount of wakefulness by 84%

62% and 60% fold during that first 3-hour recording period and concomitantly increased non rapid eye movement (NREM) and REM sleep

when compared with aCSF treatment. The sleep-inducing effect was maintained even in 3 hour after the 20 nmol AD microinjection. The maximal sleep-inducing effect was obtained at the 20 nmol dose of AD administration into the orexinergic LH (P0.05). 　Conclusion　Unilateral microinjection of AD into orexinergic zone of LH promotes NREM/REM sleep of rats.