Major depression/depressive disorder etiology

Explain the etiology and pathophysiology of major depressive disorder. 

In summary, many animal of models depressive disorders have been developed, each w ith relative advantages and disadvantages (Nestler et al., 2002). The validity of these models for human depressive disorders continues to be the subject of debate. Probably, this reflects the lack of comprehensive data on the molecular pathophysiology, genetic etiology, and relation to stress in human major depressive disorder. 

Bipolar disorder is characterized by episodes of mania or hypomania, which include hyperactivity, decreased need for sleep, and a euphoric or irritable mood. Additionally, persons with bipolar disorder may have episodes of depression similar to those seen in major depressive disorder. The lifetime prevalence of severe bipolar disorder is about 1% and 3-5% if milder cases are included, afflicting men and women equally. Both bipolar disorder and major depressive disorder tend to be episodic, and in the periods of time between episodes, persons may experience few or no symptoms. The etiology of bipolar disorder is predominately genetic, with a 70% concordance in monozygotic twins. The neurobiology of bipolar disorder is less well understood, and few animal models have been developed. Treatment of bipolar disorder usually involves mood stabilizer medications, including lithium, and the anticonvulsants valproate and carbamazepine. At times, antidepressant and antipsychotic medications are also used. 

In summary, the etiology of major depressive disorder suggests a genetic component, environmental influences, and other, as yet undetermined factors. 

---