From the Guidelines
Serotonin, also known as 5-hydroxytryptamine, is a neurotransmitter that plays a crucial role in regulating various bodily functions, including mood, emotions, sleep, appetite, and digestion. As noted in the clinical practice guideline for social anxiety disorder by the Japanese Society of Anxiety and Related Disorders/Japanese Society of Neuropsychopharmacology 1, serotonin is a key target for pharmacotherapy in adults with social anxiety disorder. The guideline highlights the efficacy of selective serotonin reuptake inhibitors (SSRIs) and serotonin-norepinephrine reuptake inhibitors (SNRIs) in treating social anxiety disorder, with high treatment response rates and low dropout rates.
Key Points About Serotonin
- It is primarily found in the brain, digestive system, and blood platelets
- In the brain, serotonin helps transmit signals between nerve cells, influencing psychological functions like mood regulation
- Low levels of serotonin are associated with depression, anxiety, and sleep disorders
- Serotonin is synthesized from the amino acid tryptophan, which is obtained from the diet through foods like eggs, cheese, turkey, nuts, and salmon
- Beyond mental health, serotonin also affects physical processes including blood clotting, bone health, and digestive function The importance of serotonin in regulating mood and emotions is further emphasized by its role as a target for antidepressant medications like SSRIs, which work by increasing serotonin levels in the brain 1. Overall, serotonin plays a vital role in maintaining physical and mental health, and its dysregulation can have significant consequences.
From the Research
Definition and Roles of Serotonin
- Serotonin, also known as 5-hydroxytryptamine (5-HT), plays two important roles in humans: one central and the other peripheral, depending on the location of the 5-HT pools on either side of the blood-brain barrier 2.
- In the central nervous system, serotonin acts as a neurotransmitter, controlling brain functions such as autonomic neural activity, stress response, body temperature, sleep, mood, and appetite 2.
- As a peripheral hormone, serotonin is unique in controlling the functions of several organs, including regulating motor and secretory functions in the gastrointestinal tract, energy metabolism, hemostasis, vascular tone, heart rate, respiratory drive, cell growth, and immunity 2.
Physiological Functions of Serotonin
- Serotonin regulates almost all immune cells in response to inflammation, following the activation of platelets 2.
- It has fundamental effects on endocytosis and endosomal sorting, with the potential to enhance endocytosis through three distinct mechanisms: serotonin signalling, serotonylation, and insertion into the plasma membrane 3.
- Serotonin is also involved in the modulation of gastrointestinal motility, glucose homeostasis, and adiposity, with a causal relationship existing between circulating 5-HT levels and metabolic diseases 4.
Serotonin and Sleep-Wake Cycles
- Serotonin neurons have been implicated in the modulation of sleep-wake cycles, with impaired or altered 5-HT neurotransmission appearing to be involved in sleep disorders 5.
- Brain 5-HT levels play an important role in the circadian rhythm of sleep-wake cycles, with a rapid turnover rate of 5-HT necessary for maintaining normal circadian rhythms 5.
Synthesis and Regulation of Serotonin
- Serotonin is synthesized from the essential amino acid tryptophan by the rate-limiting enzyme tryptophan hydroxylase (TPH), with two isoforms expressed in distinct cell types throughout the body 4.
- The central and peripheral pools of 5-HT are anatomically separated and act in their own distinct manners, with 5-HT unable to readily cross the blood-brain barrier 4.