The role of serotonin / neurotransmitters in depression
Patients with depression have lower levels of certain neurotransmitters such as serotonin or norepinephrine in the brain than healthy people. According to current scientific knowledge, it is assumed that this lack of free neurotransmitters plays a decisive role in the development of depression. Antidepressants, i.e. drugs used to treat depression, intervene in precisely this cycle and increase the concentration of free neurotransmitters.
However, research into depression is far from complete. In addition to the neurotransmitters, numerous other components seem to play a role in the development of the disease.
Read more on this topic: Causes of depression
What are neurotransmitters?
Neurotransmitters are messenger substances that transmit important information about the body from one nerve cell to the other. Information is passed on in the nerve cells as electrical impulses (action potentials). However, since electrical impulses cannot jump from one nerve cell to the other, a messenger substance is required that transmits the impulse in a suitable way. The place of signal transmission is called the synapse.
If an electrical impulse arrives at a nerve cell, neurotransmitters are released into the so-called synaptic gap, which lies between the nerve cells.The neurotransmitters bind to receptors on the surface of downstream nerve cells and trigger another electrical impulse. The neurotransmitters are then inactivated and taken up again by the preceding nerve cell.
There are many different neurotransmitters. Serotonin, noradrenaline and dopamine play a major role in depression.
What is Serotonin?
Serotonin is one of many neurotransmitters and also a tissue hormone. In addition to the brain (central nervous system), it also occurs in the periphery of the body and has an effect on the cardiovascular system and the gastrointestinal tract, for example.
Read more about serotonin on the main page: Serotonin
There are various serotonin receptors in the human body that serotonin can bind to. Due to the different types of receptors, it is possible that the same messenger substance can trigger different signal cascades and reactions in the body. In the brain, for example, serotonin has numerous effects. Serotonin affects mood. It evokes a feeling of serenity, calm and relaxation and dampens negative feelings such as tension, fear, aggressiveness and sadness. Serotonin also affects the feeling of hunger. Serotonin also has an influence on the sleep-wake rhythm, it promotes wakefulness. Sexual function and behavior are also determined by the neurotransmitter. Serotonin has an inhibitory effect on sexuality. This explains why antidepressants that cause an increase in serotonin levels can often cause sexual dysfunction.
Serotonin itself is not used as a drug. One of the reasons for this is that it cannot cross the blood-brain barrier, so it would not get into the brain after ingestion as a tablet or infusion. Nonetheless, serotonin plays an important role in drug therapy, and not just for treating depression. Most common antidepressants inhibit the uptake of serotonin in nerve cells. This means that more serotonin is available in the synaptic gap for signal transmission.
Read more on this topic: Therapy for depression
Can you measure a serotonin deficiency?
A serotonin deficiency in the brain cannot be reliably measured. There are laboratory tests in which the serotonin level can be measured, but this only plays a role in diseases that are characterized by an excessively high serotonin level (e.g. some cancers). The measurement of the serotonin level for the diagnosis of depression is difficult if not impossible, since the serotonin measured in the blood or urine or the breakdown products of the serotonin give no indication of the concentration of the messenger substance in the brain. However, only the serotonin present in the Gehrin plays a role in depression. In addition, only about 1% of the serotonin in the human body is in the brain. Therefore, a serotonin deficiency in the brain cannot be reliably measured. Attempts to measure the serotonin level in the nerve water (liquor) have not yet produced any useful results.
What is normal serotonin level?
Since the measurement of the serotonin level does not play a role in the diagnosis and therapy of depression, there are no statements about which serotonin level is normal. The concentration of serotonin and its breakdown products can be measured in the blood and urine, but this has no relevance for the diagnosis of depression and can only reveal an excess of serotonin.
How can I increase serotonin levels in the brain?
Serotonin and its precursors are found in numerous foods. Among other things in chocolate, walnuts and various fruits. It is therefore suggested that by consuming these foods one can increase serotonin levels in the brain. On the one hand, however, the serotonin concentration in these foods is usually not high enough, on the other hand, serotonin cannot cross the blood-brain barrier. This means that it can only get into the brain if it was also produced there.
Some of the foods mentioned above do not contain serotonin but rather the precursor tryptophan. This can get into the brain, where it is broken down into serotonin. However, the concentration in the food is usually insufficient to influence mood or other behavior that is influenced by serotonin. In general, however, a healthy and balanced diet (long-acting carbohydrates, sufficient omega-3 fatty acids) should lead to a better mood.
Read more on the topic: Iron Deficiency and Depression - What Is the Connection?
One possibility to increase the serotonin concentration in the brain is sport: During sport, tryptophan accumulates due to the breakdown processes. Tryptophan can cross the blood-brain barrier and is converted to serotonin. So this means that exercise can increase the concentration of serotonin in the brain.
Regardless of this, drug therapy with antidepressants is the most effective way of increasing the serotonin concentration in the brain in depressed patients. Nonetheless, exercise in the fresh air, for example, is something that depressed patients strongly recommend. Not least because the serotonin level in the brain can rise through physical activity.
Read more on this topic: Effect of antidepressants and therapy for depression
What role does serotonin play in the gut?
In the intestine, serotonin plays a role in intestinal activity, among other things. Serotonin brings about an interplay of contraction and relaxation of the intestinal muscles and thus promotes the typical digestive movements, the so-called peristalsis. Serotonin also plays a role in relaying pain in the abdomen to the brain. Serotonin can also cause nausea and vomiting.
What role does dopamine play in depression?
Dopamine also plays a role in the development of depression. A lack of dopamine can promote the development of depression. However, the neurotransmitters serotonin and norepinephrine play a more decisive role in the clinical picture of depression. Dopamine, on the other hand, plays a very important role in diseases such as Parkinson's disease and schizophrenia.
What role does norepinephrine play in depression?
Like serotonin, norepinephrine is a neurotransmitter and hormone. Like serotonin, norepinephrine functions, among other things, as a messenger substance to pass on information in the form of impulses from one nerve cell to another. A lack of noradrenaline in the synaptic cleft is partly responsible for the depressive symptoms. A norepinephrine deficiency causes a reduction in drive, motivation and concentration.
Antidepressants, among other things, are used to treat depression, which counteract the noradrenaline deficiency. Here, drugs are used that inhibit the reuptake of noradrenaline into the nerve cells, so-called selective noradrenaline reuptake inhibitors (SNRI) or selective serotonin and noradrenaline reuptake inhibitors (SSNRI). The treatment means that norepinephrine remains in the synaptic gap longer and can therefore act longer on the downstream nerve cells. This leads to a reduction in symptoms, an improved mood and increased drive.
What causes the neurotransmitters in the brain to be disrupted?
So far it is not clear how and why the neurotransmitter system in the brain changes in depression. The fact is that certain neurotransmitters such as serotonin and noradrenaline seem to be present in reduced concentrations in depression. This causes the depressive symptoms. However, depression is a combination of many different factors. Genetic aspects also seem to play a role. For example, some people are more prone to developing depression than others.
The clinical picture of depression is currently still the subject of research. The fact that not all depressed patients respond equally well to antidepressants indicates that the disorders in the neurotransmitter system are not the only causal component in the development of depression.
Read more on this topic: Causes of depression