CSF markers in sleep neurobiology

The cerebrospinal fluid has been used in the study of normal and pathological conditions of the central nervous system for more than a century. CSF analysis has also been applied to the study of sleep and its disorders but methodological aspects have often limited the results. The discovery of the hypocretin system (also known as orexin system) and its involvement in the pathophysiology of narcolepsy has opened a new field in the diagnosis of hypersomnia by CSF analysis and has revived the interest on this subject in sleep medicine. Older and new lines of research involving CSF measurement of hypocretin and other neurotransmitters in sleep and its disorders are reviewed.