Circadian rhythms have evolved in almost all organisms enabling them to anticipate alternating changes in the environment. As a consequence, the circadian clock controls a broad range of bodily... Show moreCircadian rhythms have evolved in almost all organisms enabling them to anticipate alternating changes in the environment. As a consequence, the circadian clock controls a broad range of bodily functions including appetite, sleep, activity and cortisol levels. The circadian clock synchronizes itself to the external world mainly by environmental light cues and can be disturbed by a variety of factors, including shift-work, jet-lag, stress, ageing and artificial light at night.Interestingly, mood has also been shown to follow a diurnal rhythm. Moreover, circadian disruption has been associated with various mood disorders and patients suffering from depression have irregular biological rhythms in sleep, appetite, activity and cortisol levels suggesting that circadian rhythmicity is crucially involved in the etiology and pathophysiology of depression.The aim of the present review is to give an overview and discuss recent findings in both humans and rodents linking a disturbed circadian rhythm to depression. Understanding the relation between a disturbed circadian rhythm and the etiology of depression may lead to novel therapeutic and preventative strategies. Show less
The suprachiasmatic nucleus (SCN) functions as a circadian clock that drives 24-hour rhythms in physiology and behavior. The SCN neurons function as cell-autonomous oscillators, and the... Show more The suprachiasmatic nucleus (SCN) functions as a circadian clock that drives 24-hour rhythms in physiology and behavior. The SCN neurons function as cell-autonomous oscillators, and the production of a coherent SCN rhythm is dependent upon synchronization among single cells. We investigated how changes in phase-synchronization between individual cells effect the ability of the SCN to phase-shift its rhythm. Empirical and modelling studies revealed larger phase-shifts in synchronized SCN than in desynchronized SCN. The major external stimulus affecting the SCN is light. We explored the ability of melanopsin and rod- and cone photoreceptors to mediate the effects of light on SCN discharge, and found that melanopsin and cones are able to mediate light responses of the SCN. Studies performed in nocturnal species have indicated that the SCN’s rhythmicity is also influenced by the animal’s own behavioral activity. We assessed the effect behavioral activity on the amplitude of the circadian rhythm in SCN electrical discharge rate in the day-active Arvicanthis ansorgei. The results showed acute enhancements of SCN discharge during episodes of behavioral activity. The studies described in this thesis indicate that the SCN is part of a brain network that includes the retina and areas involved in behavioral activity and sleep. Show less
