Mood disorder is known to be caused by life events and psychosocial factors. Nevertheless, evidence has been found that strongly suggest that biological factors such as genes and neurotransmitters play a role in mood disorders such as bipolar depression and substance use disorders (cite). In this paper, a milder unipolar depression, dysthymia, will be examined as whether biological factors play a role in it. Dysthymia is defined as a mild chronic depression which last at least two years (cite). It must consist two of the following symptoms: appetite disturbances, sleeping problems, low energy, low self-esteem, low concentration, inability to make decisions and sense of hopelessness; the person must not have other disorders or consume pharmacological substances that have physiological effects (cite).
Little research has been conducted into investigating the genetic factors and no or weak evidence of the role of genetic factors in dysthymia was found up to this stage (cite, book).
Nevertheless, several studies found abnormalities in neurotransmitters activities and dysregulation of neuroendocrine (cite) in dysthymic patients. Rabindran, ........ have found higher cortisol (a certain type of hormones) levels and lower "platelet MAO activity" in dysthymic patients than that in control, and low pre-treatment serotonin levels was associated with high depression rates. (cite, p.). Furthermore, patients responded to the treatment were also found to have significantly lower pre-treatment but higher post-treatment serotonin levels compared to patients who didn't respond to the treatment. They have significantly different amount of urinary metabolites compared to nonresponders, suggesting the existence of a subgroup of dysthymic patients and a biological substrate.
Other than that, Knutson, D.J. (1998) has demonstrated response in terms of less negative emotions in normal volunteers without mood disorders after administration of an antidepressant, paroxetine. The decrease of negative emotions such as sadness and hostility is significantly large in the...