Animal models of depression

Animal models of depression are research tools used to investigate depression and action of antidepressants as a simulation to investigate the symptomatology and pathophysiology of depressive illness or used to screen novel antidepressants.

Major depressive disorder, also called "clinical depression" or often simply "depression", is a common, long-lasting and diverse psychiatric syndrome that significantly affects a person's thoughts, behavior, feelings and sense of well-being. Symptoms include low mood and aversion to activity. Depressed people may also feel sad, anxious, empty, hopeless, worried, helpless, worthless, guilty, irritable, hurt, or restless. They may lose interest in activities that once were pleasurable, experience loss of appetite or overeating, have problems concentrating, remembering details, or making decisions, and may contemplate or attempt suicide. Insomnia, excessive sleeping, fatigue, loss of energy, or aches, pains, or digestive problems that are resistant to treatment may also be present.

About one in six people in the U.S will succumb to depression at some point during their life span, and according to the World Health Organization, depression is projected to reach second place as leading contributor to the global burden of disease by the year 2020. The effects of current antidepressant drugs are often significantly delayed, with improvements beginning around 3–6 weeks after treatment is started. Despite the clinical success of many antidepressant drugs, such as tricyclic antidepressants (TCAs), monoamine oxidase inhibitors (MAOIs), and serotonin reuptake inhibitors (SRIs), many individuals' symptoms are not adequately alleviated by medication alone, and other methods of treatment may be recommended.

It is difficult to develop an animal model that perfectly reproduces the symptoms of depression in patients. Many animals lack self-consciousness, self-reflection, and consideration; moreover, hallmarks of the disorder such as depressed mood, low self-esteem or suicidality are hardly accessible in non-humans. However, depression, as other mental disorders, consists of endophenotypes that can be reproduced independently and evaluated in animals. An ideal animal model offers an opportunity to understand molecular, genetic, and epigenetic factors that may lead to depression. By using animal models, the underlying molecular alterations and the causal relationship between genetic or environmental alterations and depression can be examined, which would afford a better insight into pathology of depression. In addition, animal models of depression are indispensable for identifying novel therapies for depression.

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