Effect of clonidine and yohimbine on sleep in man: polygraphic study and EEG analysis by normalized slope descriptors.

An all-night polygraphic study of sleep was carried out in 6 healthy volunteers acutely medicated with clonidine (225 micrograms), yohimbine (15 mg), a combination of both drugs or with placebo at random order under simple blind conditions. The conventional scoring of sleep stages was extended by an on-line analysis of the EEG according to Hjorth. Clonidine, an agonist at alpha2 receptors, induced increases of the stages 2 and 3 + 4 but a decrease of REM sleep; the reduction of the parameters mobility and complexity during non-REM sleep signified synchronization of the EEG. Yohimbine, an antagonist at the same receptor sites, enhancing noradrenaline release, increased stage 1 and REM sleep, but decreased the stages 2 and 3 + 4; increases of mobility during REM and non-REM sleep signified desynchronization. The combined treatment with clonidine + yohimbine reduced REM sleep, but not as extensively as clonidine alone; the Hjorth parameters were without significant alterations compared to placebo. The physiological hypotonia was enhanced by clonidine and the combined treatment with clonidine + yohimbine. These results favour the hypothesis of a noradrenergic facilitation of REM sleep.