The activity of serotonin systems have been to mood.  Tryptophan depletion leads to symptom relapse in people in remission from depression.

Tryptophan depletion

Studies have shown that low amounts of serotonin in the brain have been implacated in anxiety. One way this phenomena was shown was via a force swim test, as well as through learned helplessness.
           

Serotonin's Role in Anxiety

Cellular: 
-Simultaneous inhibition and excitation
-Complicated cell responses
Behavioral: 
-Anxiety
-Depression 
-Mood

University of Vermont

- Abbreviated 5-HT from chemical name 5-hydroxytryptamine 
- Synthesized from the tryptophan amino acid tryptophan, which is only obtained from diet.
- Produced and concentrated in the raphe nuclei of the midbrain and brainstem 
- About 200,000/80 to 90 billion neurons are serotonergic but they exert influence throughout the entire brain 
- Controls sleep states, mood, sexual behavior, and anxiety 
- At least 14 types of serotonin receptors (all but one is metabotropic) 
-Precursor to melatonin

Serotonin Neurotransmitter 

Serotonin Reference Library

Serotonin Brain Pathways 

1. Tryptophan obtained through diet
2. Converted to serotonin (generally in terminal)
3. Serotonin packaged into vesicles
4. Monoamines are put into vesicles by vesicular monoamine transporter
Exocytosis
5. Binds to receptors
6. Transporters (5-HT) bring serotonin back into the cell
7. 5-Hydroxyindolacetic acid (5-HIAA): serotonin metabolite—breaks it down after reuptake

Life of a Serotonin Neurotransmitter 

Serotonin Roles and Functions

Family	Type	Mechanism

5-HT1	Metabotropic	decreasing cellular levels of cAMP, 5-HT1A can be a           somatodendritic autoreceptor. 5-HT1B and 1D are terminal autoreceptors.

5-HT2	Metabotropic	Excitatory

5-HT3	Ionotropic	depolarizing plasma membrane- cation channel, quick action and quick desensitization.

5-HT4	Metabotropic	increasing cellular levels of cAMP

5-HT5A	Metabotropic	inhibiting adenylate cyclase activity.

5-HT7	Metabotropic	increasing cellular levels of cAMP


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