Animal Models of Depression and Chronic Fatigue Syndrome

Abstract

Major depression is one common mental illness and proliferating health problem mainly affects the person thought, behavior, feeling and emotional experiences. As per WHO, this is also responsible for morbidity with a prevalence of about 15–20% worldwide (Kulkarni et al. 2009). Common symptoms associated with the depression are irritable mood, decreased interest in pleasurable activities (anhedonia), significant weight loss or gain sometimes, insomnia, loss of energy, feeling of worthlessness or excessive guilt, decreased concentrating power, and increase in suicidal tendencies. In the old time, major depression was considered to be an old-age related mental disorder but the current trends reveal an increased percentage of younger populations being affected from its consequences (Fiske et al. 2009). There are number of evidences about its cause but the major etiological factors include increase mental stress, disturbed sleep and reduced level of monoamines in the brain. According to monoamine hypothesis increased cholinergic and decreased adrenergic activity also increase the instance of depression. Instead of this various monoamines like norepinephrine, serotonin and dopamine help to regulate the physiological functions of brain like mood, reward processing, appetite, sleep and cognition etc. The functions like reward, emotion are regulated by several regions of the brain and these directly interconnected to limbic regions which play essential role in depression (Hasler 2010). It is confirmed by the post-mortem and neuroimaging reports that patients with low volume of grey-matter and glial cell density in the prefrontal cortex and the hippocampus regions are more prone toward the cognitive dysfunctions like depression (Drevets et al. 2008). No doubt there are plentiful medications available for the treatment of depression but the psychological counseling (psychotherapy) is also very effective for most patients. Several antidepressants are available to treat depression such as atypical antidepressants, selective serotonin reuptake inhibitors (SSRI), selective norepinephrine reuptake inhibitors (SNRI) etc. but their produce long term and dose dependent adverse effects.