The daily rhythmicity of biological rhythms and the sleep wake cycle is regulated by the day night cycle that synchronizes the internal circadian clock to environmental 24 hour conditions. The circadian clock, located in the suprachiasmatic nucleus of the hypothalamus, in turn regulates a wide range of physiological and behavioral functions including hormone synthesis, gene expression, immune function and metabolism. The regulation and deregulation of circadian rhythmicity has important consequences for health and well being. Misalignment of the internal circadian timing system with the light dark cycle, for example in shift work, frequent trans-meridian travel but also during neurodegenerative disease and aging, significantly increases risks of cardiovascular disease, cancer and obesity, and decreases immune function and cognitive performance. In many cases, appropriate use of light therapies as a counter measure to resynchronize the circadian timing system can improve health and increase performance. Thus, understanding the neural networks and mechanisms involved in the light synchronization of circadian rhythms and sleep is crucial for progress towards clinical applications. The presentations during this symposium will illustrate recent studies in this area of research, for example on sleep regulation in rhythmic and arrhythmic species of an African rodent model. The mechanisms of daily and seasonal control of hormones, clock gene function and activity will also be analyzed in a seasonally hibernating species from northern Africa . The interactions between the light-dark cycle, serotonin and corticosterone that modulate gene expression in brain regions involved in mood regulation and their possible consequences in seasonal affective disorder (SAD) will also be examined. We will also review the physiological roles of melanopsin, a novel photopigment recently discovered in the human retina, and new applications that aim to use melanopsin to restore vision in the blind.
A study of sleep in a microphthlamic species of rodent
Adhil Bhagwandin, University of Witswatersrand , South Africa
Mechanisms of encoding photoperiod information in the suprachiasmatic nucleus of a desert hibernator the Jerboa Jaculus orientalis
Nouria Lakhdar-Ghazal, University Mohammed V, Morocco
Reducing retinal input to the circadian clock alters entrainment and dampens corticosterone rhythms: implications regarding seasonal affective disorder
Gary E. Pickard, University of Nebraska , USA
New perspectives for a new circadian photopigment in the human retina
Howard M Cooper, INSERM U846-University of Lyon, France