The neurochemistry of the sleep-wakefulness cycle and Parkinson's disease

Parkinson's disease (PD) is one of the most socially relevant illnesses. Sleep disturbances in PD are common and manifold; they are present, according to different data, in 45-98% of all patients and include insomnia, parasomnia, hypersomnia, and other symptoms. Many of these symptoms appear several years before the development of movement disorders and may be regarded as early predictors of PD. We review the possible roles of the dopaminergic, orexin/hypocretinergic, and melaninergic cerebral structures in the development of PD sleep disorders, such as excessive daytime sleepiness, rapid eye movement sleep behavior disorders (RBD), and restless legs syndrome.