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Neurotransmitters Associated with Depression

Depression has been linked with reduced action of serotonin, norepinephrine and dopamine in the brain [ref]: 

Serotonin has many functions, one of which seems to be the production of a feeling of contentedness, connectedness and peacefulness.  When levels of serotonin are reduced, people tend to feel more anxious, stressed, irritable, aggressive, impulsive and depressed.   SSRI antidepressants seem to have their effect by increasing the levels of serotonin in the brain available for signaling.  There are various types of serotonin receptors in the brain, and their functions are not completely understood.  Increased levels of serotonin 2A receptor in the brain have been associated with having Depression as well as with experiencing more frequent depressive thoughts [ref]; this may reflect the brain's attempt to compensate for overall low levels of serotonin, but another hypothesis is that serotonin 2A receptors might actually be involved in the actual process of Depression, because blocking these receptors with antidepressants like Mirtazepine is a way to treat Depression.  Stimulating serotonin 1A post-synaptic receptors is also thought to be a way to treat Depression.

Norepinephrine (aka Noradrenaline) seems to produce, among other things, a feeling of excitement, interest, initiative, power and dominance.  Low levels of this neurotransmitter can lead to states of low energy, loss of interest or motivation, and feelings of defeat and low self-esteem.

Dopamine is involved in focusing a person's interest on something, producing a feeling of incentive, and allowing a person to anticipate and to experience a feeling of reward, success and pleasure.   When dopamine's actions are blocked, a person will lose motivation, feel apathetic, hopeless, and lose a capacity for experiencing pleasure. 

Glutamate is gaining increasing attention as a possible factor in the biology of Depression. There is growing evidence that elevated levels of glutamate may lead to Depression, and that blocking the actions of glutamate with drugs called NMDA antagonists can have a rapid effect on improving depressive symptoms [ref].

 

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Brain Regions

Hormones