Article

Daily rhythms in physiological and behavioural processes are controlled by a
network of circadian clocks. In mammals, at the top of the network is a master
clock located in the suprachiasmatic nuclei (SCN) of the hypothalamus. The
nocturnal synthesis and release of melatonin by the pineal gland are tightly
controlled by the SCN clock. Several roles of melatonin in the circadian system
have been identified. As a major hormonal output, melatonin distributes temporal
cues generated by the SCN to the multitude of tissues expressing melatonin
receptors. In some target tissues, these melatonin signals can drive daily
rhythmicity that would otherwise be lacking. In other target structures,
melatonin signals are used for the synchronization (i.e., adjustment of the
timing of existing oscillations) of peripheral oscillators. Due to the expression
of melatonin receptors in the SCN, endogenous melatonin is also able to feedback
onto the master clock. Of note, pharmacological treatment with exogenous
melatonin can synchronize the SCN clock. From a clinical point of view, provided
that the subject is not exposed to light at night, the daily profile of
circulating melatonin provides a reliable estimate of the timing of the human
SCN. During the past decade, a number of melatonin agonists have been developed.
These drugs may target the SCN for improving circadian timing or act indirectly
at some downstream level of the circadian network to restore proper internal
synchronization.
CI - Copyright (c) 2014 Elsevier Masson SAS. All rights reserved.

Langue : ANGLAIS