Adenosine and caffeine modulate circadian rhythms in the Syrian hamster

Extracellular adenosine accumulates in some brain areas during sleep deprivation. In Syrian hamsters, both sleep deprivation and adenosine Al agonists can inhibit phase shifts of circadian rhythms to light at night. Sleep deprivation in the day (sleep period) can shift circadian phase. We examined whether the Al agonist N-CHA mimics this effect. N-CHA (i.p. or i.c.) in the mid-sleep period induced dose-dependent shifts similar to those induced by 3 h sleep deprivation. The adenosine antagonist caffeine administered systemically at the mid-sleep period induced arousal without shifts, and dose-dependently attenuated shifts to a 3 h sleep deprivation procedure (running in a novel wheel). Adenosine may participate in resetting of the circadian clock by manipulations of behavioral state. NeuroReport 12:2901-2905 (C) 2001 Lippincott Williams & Wilkins.