Dim light melatonin onset in psychiatric disorders

Introduction In 1999, Lewy proposed that the dim light melatonin onset (DLMO) was the most useful marker for human circadian phase position and that the DLMO was optimally obtained by sampling blood or saliva in the evening at intervals of 30 minutes or less under conditions of less than 30 to 50 lux. The DLMO is now commonly used both experimentally and in clinical practice for objectively assessing the functioning of the body's biological clock. Biological clock disturbances are reflective of more general sleep–wake rhythm disturbances, but are being increasingly used for diagnosing broader conditions, such as several psychiatric disorders, that are associated with it. Furthermore, DLMO has been used for identifying optimal application times for treatments, such as bright light therapy and exogenous melatonin treatment. In this chapter the role of DLMO in the diagnosis and treatment of psychiatric disorders is discussed. Circadian pacemaker and dim light melatonin onset Circadian pacemaker Molecular mechanisms regulating the mammalian biological clock are present in all cells. These mechanisms consist of gene–protein–gene feedback loops in which proteins downregulate their own transcription and stimulate the transcription of other clock proteins. The mammalian biological clock consists of a hierarchy of oscillators, the central coordinator of which is found in the brain, formed by the cells of the suprachiasmatic nuclei (SCN) within the anterior hypothalamus [1].