Serotonin is a neurotransmitter that is most commonly known for its role in the brain, where it is believed to be one of the main factors influencing mood. However, it also has many other functions throughout the body, such as regulating digestion, sleep, and cardiovascular function! Read on to learn more about this fascinating neurotransmitter compound, the multiple roles in plays throughout the body, and some of the lifestyle, dietary, and other factors that can influence it! What is Serotonin?
Serotonin – also known as 5-hydroxytryptamine , or “5-HT” for short – belongs to the family of neurotransmitters called catecholamines , and acts as a very important biochemical messenger throughout the brain and the digestive system.
Serotonin is synthesized from the amino acid tryptophan by the enzyme tryptophan hydroxylase .
In humans, it is found primarily in the central nervous system (CNS), gastrointestinal tract, and blood platelets.
It is responsible for regulating many important physiological functions throughout the body and brain, including neurotransmission, gastrointestinal motility, hemostasis, and cardiovascular integrity [ 1 ].
Serotonin is best-known for its role in the brain, where it acts as one of the major neurotransmitters that allows neurons to communicate with each other.
While serotonin’s actions in the brain are diverse and highly complex, it is most well-known for its purported involvement in mood and emotion.
For example, serotonin is famous for its involvement in depression , and the majority of the most common and widely-used antidepressants primarily target the brain’s serotonin system. Nonetheless, it also plays a role in other mood-related processes, such as aggression, impulsivity, and social dominance [ 2 ].
Serotonin’s role in psychological processes is highly studied by scientists, and many studies suggest that the levels and overall activity of this key neurotransmitter can have significant effects on mood and emotion.
Researchers have a variety of ways of influencing serotonin activity. For example, acute tryptophan depletion (ATD) is one experimental method for artificially reducing serotonin levels throughout the body (because tryptophan is a necessary “ingredient”, or “ metabolic precursor ” for making serotonin – and the body and brain can’t produce any without it). Depleting serotonin levels via ATD has been associated with “low” moods, increased irritability, and increased aggression [ 3 ].
Serotonin is considered a significant circulating hormonal factor that has been implicated in normal cardiovascular function, either by acting directly on heart cells, or by stimulating chemosensitive nerves from the heart [ 4 ].
Patients with carcinoid tumors (a rare type of slow-growing cancer) have elevated levels of serotonin activity in the cardiovascular system, which has been associated with certain symptoms such as arrhythmia, which can contribute to blood flow blockage and valvular fibroplasia [ 5 ].
Additionally, growing mouse embryos that are exposed to dramatically elevated levels of serotonin (either due to high concentrations of 5-HT itself, or treated with high levels of selective serotonin reuptake inhibitors (SSRIs)) have been reported to show abnormal growth in many different parts of their developing cardiovascular system [ 4 ].
In the gastrointestinal tract, serotonin initiates responses like nausea, intestinal secretion, and peristalsis, and has also been implicated in gastroenteric diseases like irritable bowel syndrome [ 6 ].
The secretory effects of serotonin are believed to be mediated through a variety of different specialized 5-HT receptors, such as 5-HT2A [ 7 ].
Serotonin-producing cells in the mouse brain have been reported to play an essential role in maintaining proper body temperature, and regulating breathing [ 8 ].
One animal study (in TPH2 -knockout rats) suggests that 5-HTP plays a crucial role in balancing the control systems for breathing and temperature, especially during early development [ 9 ].
Neurons that primarily use serotonin have been found in high concentrations across many different brain regions that are believed to be involved in respiratory control [ 10 ].
Serotonin is believed to be responsible for controlling the contraction of vascular smooth muscle cells throughout the body – these muscle cells are particularly prominent throughout the circulatory system, where they are responsible for controlling blood flow by constricting or dilating blood vessels. It is believed that the “S2” type of serotonergic receptor, in particular, plays a key role in this function [ 11 ].
In fact, some of the earliest scientific investigations of serotonin (5-HT) was due to its vasoconstrictive effects – it generally wasn’t until later that its other physiological and psychological roles became apparent.
For example, animal studies have reported that intravenous injections of serotonin can induce a wide variety of responses in the cardiovascular system, leading to increases or decreases in blood pressure, depending on where and when it is active in the body [ 12 , 13 ].
Serotonin can also control blood pressure using other, “indirect” mechanisms, such as by amplifying the response of other vasoactive substances such as NET, angiotensin II , and histamine [ 14 ].
Serotonin receptors have been identified in all the major types of bone cell ( osteoblasts , osteocytes , and osteoclasts ) [ 15 ].
Recent data suggests that gut-derived serotonin may mediate the skeletal effects of LDL receptor -related protein 5 .
Additionally, some evidence suggests that use of SSRIs ( selective serotonin reuptake inhibitors ) – which increase serotonin levels throughout the body – may be associated with reduced bone mass, increased bone loss, and increased risk of fractures [ 15 ].
Finally, some studies have even suggested a direct stimulatory effect of serotonin on bone formation pathways [ 16 ]. However, other studies have reported inhibitory effects, indicating a potentially complex role of serotonin in bone formation [ 17 ].According to some research, serotonin may play a critical role in the development and growth of several different major bodily organs, such as the heart and the lungs [ 18 , 19 , 20 ].In both mice and people, high levels of 5-HT2B in the lungs have been associated with the development of pulmonary hypertension, further suggesting a direct influence of serotonin on lung growth and function [ 21 , 20 ].5-HTP is believed to be involved in many of the psychological and behavioral symptoms involved in major eating disorders, such as […]