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The biology of depression is the attempt to identify a biochemical origin of depression, as opposed to theories that emphasize psychological or situational causes. Scientific studies have found that different brain areas show altered activity in humans with major depressive disorder (MDD). [1]
The neurotrophic hypothesis of depression [1] proposes that major depressive disorder (MDD) is caused, at least partly, by impaired neurotrophic support.Neurotrophic factors (also known as neurotrophins) are a family of closely related proteins which regulate the survival, development, and function of neurons in both the central and peripheral nervous systems.
The pharmacology of antidepressants is not entirely clear.. The earliest and probably most widely accepted scientific theory of antidepressant action is the monoamine hypothesis (which can be traced back to the 1950s), which states that depression is due to an imbalance (most often a deficiency) of the monoamine neurotransmitters (namely serotonin, norepinephrine and dopamine). [1]
After release into the synaptic cleft, monoamine neurotransmitter action is ended by reuptake into the presynaptic terminal. There, they can be repackaged into synaptic vesicles or degraded by the enzyme monoamine oxidase (MAO), which is a target of monoamine oxidase inhibitors, a class of antidepressants. [citation needed]
Major depressive disorder is believed to be caused by a combination of genetic, environmental, and psychological factors, [1] with about 40% of the risk being genetic. [5] Risk factors include a family history of the condition, major life changes, childhood traumas, environmental lead exposure , [ 16 ] certain medications, chronic health ...
The monoamine hypothesis was originally proposed based on observations that reserpine, a drug which depletes the monoamine neurotransmitters, produced depressive effects in people, [201] and that certain hydrazine antituberculosis agents like iproniazid, which prevent the breakdown of monoamine neurotransmitters, produced apparent ...
Monoamine precursors are precursors of monoamines and monoamine neurotransmitters in the body. [ 1 ] [ 2 ] The amino acids L -tryptophan and L -5-hydroxytryptophan (5-HTP; oxitriptan) are precursors of serotonin and melatonin , while the amino acids L -phenylalanine , L -tyrosine , and L -DOPA (levodopa) are precursors of dopamine , epinephrine ...
However, the hypothesis is incomplete, as several lines of evidence suggests that depression is more than just a monoamine imbalance. For example, antidepressants usually take several weeks to reduce a patient's depressive symptoms, which is inconsistent with the finding that monoamine levels are affected within hours of using antidepressants. [5]