Biological aspects of depression.

In most cases, depression involves the interaction of biological and psychosocial factors. The impact of biological factors seems to be more prominent in major depressive syndrome, where typical symptoms and signs such as decrease in weight, changes in libido, dysmenorrhea, and sleeping disorders cannot be explained on psychodynamic grounds alone. Some of the symptoms and signs typical of patients suffering from depression reflect a primary disorder of biochemical and neurophysiological functions and are not commonly found in other forms of psychic disturbances. Studies related to monoamine (noradrenaline, serotonin or 5-HT, dopamine) metabolism have assumed a major role in biochemical research into depression; this research now also includes studies on other central neurotransmitters such as GABA and glutamic acid, and neuropeptides like somatostatin and corticotropin-releasing factor (CRF). Several theories have been suggested for the biochemical background of depression, and these hypotheses can now be tested using new and sophisticated research methods. Recent progress in understanding receptor structure and function and the regulation of neuroendocrine functions will substantially increase our knowledge of the biological deviations in depression and eventually lead to better drugs and treatment strategies. In the following, current perspectives on the biology of depressive disorders are introduced. It seems clear that susceptibility to depression is linked with deviations in presynaptic and postsynaptic neurotransmitter turnover and function. These, in turn, may lead to alterations in other regulatory mechanisms, such as the neuroendocrine and immune systems.