The influence of chronic caffeine administration on sleep parameters in the cat.

Caffeine (20 mg/kg/day) was administered per os to 5 cats for 21 days and sleep parameters were measured both during drug administration and over the withdrawal phase. The initial effect of caffeine was a marked increase in waking. As the animal habituated to the stimulant action of the methylxanthine, however, total sleep time normalized, although time spent in Stage II slow wave sleep (S2) remained below, and Stage I slow wave sleep (S1) above, control levels throughout the period of drug administration. In contrast, a significant increase in the S2/S1 ratio was recorded as soon as caffeine treatment ended, and this parameter remained elevated for about 30 days. Chronic caffeine administration has been previously shown to increase the number of central adenosine receptors, and it has also been reported that adenosine agonists increase S2 at the expense of S1. The present data were thus interpreted as indicating that the action of caffeine on sleep may be mediated at a central adenosine receptor site. Results also imply that changes induced in this receptor population by chronic caffeine administration last for at least 30 days after the drug is withdrawn.