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Current developments in Seasonal Affective Disorder/Depression

Introduction
Seasonal affective disorder (SAD) is a mood disorder which is common in temperate climates. It consists of recurrent major depressive episodes mainly during the winter season when the levels of light are reduced. Otherwise known as the winter depression or winter blues, SAD can lead to major clinical depression (Welberg 2007). It is characterised by typical and atypical symptoms, which include lowered mood and hypersomnia, respectively (Michalak, et al., 2001). Depression in the winter is usually followed by remission through spring and summer, with SAD said to be more popular amongst females than males with a ratio of 3.5:1, and even 9:1 in some samples (Monteleone & Maj 2008) (Winkler et al., 2002). A range of aetiologies for SAD have been suggested including a link to serotonin and melatonin. In this essay I will explore these mechanisms, and treatments they have inspired. 

Circadian rhythm
Humans have a circadian rhythm which applies to most physiological and behavioural functions, a system which is adapted to deal with variations in the environment. For that reason, it is sensitive to changes in the endogenous circuitry that monitors circadian oscillations, which could affect the mental and physical state.

Selective serotonin reuptake inhibitors (SSRI) are in use as anti-depressants and have been shown to be useful in the treatment of SAD; these include fluoxetine and sertraline. Finally, noradrenaline has also been related to the pathogenesis of SAD. But the differential beneficial value of SSRI and selective noradrenaline reuptake inhibitors (NARI) in SAD is yet to be confirmed (Pjerk, et al., 2009)
Conclusion

In conclusion, SAD is cyclic disorder, and therefore signs and symptoms come and go according to seasonal changes. It occurs regularly at a certain time in the year but it is unknown how seasonal variations cause depression. Nonetheless, research into the mechanisms and treatments of SAD has shown there to be changes in the levels of circulating brain chemicals: serotonin and melatonin (in response to differing exposures to light and dark). Treatment for SAD includes both non-pharmacological (BLT) and pharmacological (SSRI and melatonin) methods.

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