From happiness to pain: Understanding serotonin’s function
In a study published today (August 22nd), in the scientific journal PLoS One, researchers at the Champalimaud Neuroscience Programme establish the effect of serotonin on sensitivity to pain using a combination of advanced genetic and optical techniques.
“Serotonin is a small molecule known to be implicated in a wide range of brain functions, from the control of sleep and appetite, to the regulation of complex emotional behaviours, This neurotransmitter is also popularly thought to contribute to feelings of well being and happiness, as some anti-depression medications work through increasing serotonin in the brain.” - says Zachary Mainen, CNP director and principal investigator of the Systems Neuroscience Lab.
Serotonin’s great importance led researchers to seek ways of understanding its function, but studying it has been a long-standing challenge.
“Most of the cells that produce serotonin are located in a defined cell group called the Dorsal Raphe Nucleus (DRN)” - explains Zachary Mainen. “This cell group is small and located deep in the brain, which makes targeting it difficult. In addition, other cells that produce and release different molecules are also present in the DRN, which means that general stimulation of the area may result in the release of other molecules besides serotonin.”
“To overcome the limitations of previous studies and explore the specific function of serotonin, we used a combination of light and genetics, an approach called optogenetics” - says Guillaume Dugué, a former postdoctoral researcher in the lab of Zachary Mainen. Using genetic techniques, the researchers expressed a light-sensitive protein specifically in the serotonin-producing cells of mice, so that when the researchers shone light on these cells, the cells released serotonin.
“The effect of the serotonin was clear” - says Guillaume Dugué. “Mice that we stimulated to release serotonin showed a significant decrease in sensitivity to pain, when compared with mice in the control group.”
Serotonin is a chemical created by the human body that works as a neurotransmitter. It is regarded by some researchers as a chemical that is responsible for maintaining mood balance, and that a deficit of serotonin leads to depression.
The word serotonin comes from its discovery when it was isolated in 1948 by Maurice M. Rapport and initially classified as a serum agent that affected vascular tone.1
“We devoted substantial efforts to optimising light activation of serotonin-producing cells. Overall these results provide a new level of evidence on the importance of serotonin in gating the influence of sensory inputs to behavioural outputs, a key physiological role that will help define large-scale theories of serotonin function. Moreover, it has possible implications for better understanding chronic pain treatment.” - concludes Zachary Mainen.
Here are some key points about serotonin. More detail and supporting information is in the main article.
Serotonin is a chemical created by the human body that works as a neurotransmitter.
It is regarded by some researchers as a chemical that is responsible for maintaining mood balance, and that a deficit of serotonin leads to depression.
Serotonin is created by a biochemical conversion process which combines tryptophan, a component of proteins, with tryptophan hydroxylase, a chemical reactor.
Serotonin is manufactured in the brain and the intestines. The majority of the body’s serotonin, between 80-90%, can be found in the gastrointestinal (GI) tract.
Serotonin cannot cross the blood-brain barrier, therefore, serotonin that is used inside the brain must be produced within it.
It is thought that serotonin could affect mood and social behavior, appetite and digestion, sleep, memory and sexual desire and function.
An association has been made between depression and serotonin, although scientists are unsure whether decreased levels of serotonin contribute to depression or depression causes a decrease in serotonin levels.
Selective serotonin reuptake inhibitors (SSRIs) that can affect the levels of serotonin in the body work as antidepressants and are able to relieve the symptoms of depression.
If excessive amounts of serotonin are accumulated within the body then a condition known as serotonin syndrome can occur.
Other possible ways to increase the levels of serotonin in the body include mood induction, light, exercise and diet.
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About Zachary Mainen, Principal Investigator and Director of the Champalimaud Neuroscience Programme
Zach Mainen studied psychology and philosophy at Yale University and received his PhD in Neuroscience from the University of California, San Diego in 1995. From 1995-2007 he worked at Cold Spring Harbor Laboratory, New York, first as a postdoctoral fellow and then as Assistant and Associate Professor. In 2007 Mainen moved to Lisbon, Portugal to help establish the Champalimaud Neuroscience Programme (CNP). He is currently a Senior Investigator and Director of the Programme.
As a neurotransmitter, serotonin relays signals between nerve cells (neurons), regulating their intensity.
Serotonin is widely believed to play a key role in the central nervous system, as well as in the general functioning of the body and in particular the GI tract. Studies have found links between serotonin and bone metabolism, breast milk production, liver regeneration and cell division.
As a neurotransmitter, serotonin influences both directly and indirectly the majority of brain cells. The following is a list of things that it is thought that serotonin could affect:
Mood and social behavior
Appetite and digestion
Sleep
Memory
Sexual desire and function.
In 2009 Mainen received the Senior Investigator award from the European Research Council (ERC), and in 2010 he was elected a member of the European Molecular Biology Organization (EMBO) in recognition for his work in the life sciences. Mainen’s research interests concern how brains use sensory information to guide decisions and to acquire and evaluate knowledge. His laboratory’s research combines quantitative descriptions of behavior with physiological analysis of neural systems and circuits and theoretical models of brain function.
About the Champalimaud Neuroscience Programme (CNP)
The CNP is an international programme which strives to unravel the neural basis of behaviour. The concept of the programme takes into account the fact that basic neuroscience research can have a significant impact on the understanding of brain function, which in turn may contribute to the understanding and possible treatment of neurological and psychiatric illnesses.
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