Differences in gene expression during sleep and wakefulness

Compared with our understanding of the electrophysiological correlates of s leep and wakefulness, the search for correlates at the molecular level is s till in its infancy. However, the evidence obtained so far supports the hyp othesis that reliable molecular correlates do exist. As will be summarized in this review levels of receptor binding, second messengers and protein ph osphorylation differ between sleep and wakefulness. Moreover, compelling da ta obtained in different animal species suggest that the transition between sleep and wakefulness is accompanied by significant changes in gene expres sion. Many immediate early genes, transcription factors, plasticity-related genes and mitochondrial genes are expressed at higher levels in wakefulnes s than in sleep, while a few still unknown genes are up-regulated during sl eep. The ongoing systematic screening of gene expression across behavioural states should prove crucial in elucidating the regulatory mechanisms of sl eep homeostasis and the functions of sleep.