Depression is a serious and widespread disorder which results from an interplay between genetic factors and environmental factors such as stress. Early life exposure to severe stress and acute exposure to stress appear to play a role in the development of the illness. The major theories concerning the etiology of depression involve alteration of the amines such as norepinephrine and serotonin or changes in the HPA axis that mediate stress. These theories reside at the receptor level on the surface of the cell membrane. More recent evidence suggests these are simply parts of a complex network altering second messenger systems and ultimately leading to changes in gene expression which may involve direct structural changes in the brain. These changes have been postulated to involve
'Zentralinstitut für Seelische Gesundheit, J5, D-68159 Mannheim, Germany; [email protected] neurogenesis, or alternatively synaptogenesis. This chapter reviews the evidence to date implicating such structural change.
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