Introduction
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 neurotransmitters, numerous other components seem to play a role in the development of the disease.
What are neurotransmitters?
When a nerve cell receives an electrical impulse, neurotransmitters are released into the so-called synaptic gap, which is located between the nerve cells. The neurotransmitters bind to receptors on the surface of downstream nerve cells and trigger a new electrical impulse. Subsequently, the neurotransmitters are inactivated and reabsorbed by the upstream nerve cell. There are many different neurotransmitters. Serotonin, norepinephrine and dopamine play a particularly important 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 body’s periphery and has an effect on the cardiovascular system and the gastrointestinal tract, for example. In the human body there are various serotonin receptors to which serotonin can bind.
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 has an effect on mood.
It induces a feeling of calmness, peace and relaxation and dampens negative feelings such as tension, fear, aggressiveness and sadness. Serotonin also influences the feeling of hunger. Serotonin also influences the sleep-wake rhythm, it promotes alertness.
Sexual function and behaviour are also influenced by the neurotransmitter. Serotonin has a rather inhibitory effect on sexuality. This explains why antidepressants, which cause an increase in serotonin concentration, can often cause sexual dysfunction.
Serotonin itself is not used as a drug. One reason for this is that it cannot cross the blood-brain barrier, so it would not enter the brain when taken as a tablet or infusion. Nevertheless, serotonin plays an important role in drug therapy, not only in the treatment of depression.
Most common antidepressants inhibit the reuptake of serotonin into the nerve cells. Thus, more serotonin is available in the synaptic cleft for signal transmission. In the human body there are various serotonin receptors to which serotonin can bind.
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 has an effect on mood.
It induces a feeling of calmness, peace and relaxation and dampens negative feelings such as tension, fear, aggressiveness and sadness. Serotonin also influences the feeling of hunger. Serotonin also influences the sleep-wake rhythm, it promotes alertness.
Sexual function and behaviour are also influenced by the neurotransmitter. Serotonin has a rather inhibitory effect on sexuality. This explains why antidepressants, which cause an increase in serotonin concentration, can often cause sexual dysfunction.
Serotonin itself is not used as a drug. One reason for this is that it cannot cross the blood-brain barrier, so it would not enter the brain when taken as a tablet or infusion. Nevertheless, serotonin plays an important role in drug therapy, not only in the treatment of depression.
Most common antidepressants inhibit the reuptake of serotonin into the nerve cells. Thus, more serotonin is available in the synaptic cleft for signal transmission. A serotonin deficiency in the brain cannot be reliably measured.There are laboratory chemical tests in which the serotonin level can be measured, but this only plays a role in diseases that are characterized by a too high serotonin level (for example some cancers).
The measurement of serotonin levels for depression diagnosis is difficult or even impossible, since serotonin or serotonin breakdown products measured in the blood or urine do not provide any indication of the concentration of the messenger substance in the brain. However, only the serotonin present in the brain plays a role in depression. Furthermore, only about 1% of the serotonin present in the human body is found in the brain.
Therefore, a serotonin deficiency in the brain cannot be measured reliably. Attempts to measure the serotonin level in the cerebrospinal fluid (liquor) have not yet produced any useful results. Since the measurement of serotonin levels plays no role in the diagnosis and treatment of depression, there is no information about what serotonin level is normal.
The concentration of serotonin and its breakdown products can be measured in blood and urine, but this has no relevance for the diagnosis of depression and can only reveal an excess of serotonin. Serotonin and its precursors are present in numerous foods. Among others, in chocolate, walnuts and various fruits.
It is therefore thought that the intake of these foods can increase the serotonin concentration in the brain. On the one hand, however, the serotonin concentration in these foods is usually not high enough, and on the other hand serotonin cannot cross the blood-brain barrier. This means that it can only reach the brain if it has been produced there.
Some of the above mentioned foods do not contain serotonin but the precursor tryptophan. This can reach the brain and be broken down to serotonin. However, the concentration in the food is usually not sufficient to influence the mood or other behaviour influenced by serotonin.
In general, however, a healthy and balanced diet (long-acting carbohydrates, sufficient omega-3 fatty acids) should lead to a better basic mood. One way to increase the serotonin concentration in the brain is sport: during sport, increased tryptophane is produced by degradation processes. Tryptophane can cross the blood-brain barrier and is converted to serotonin.
This means that sport can increase the serotonin concentration in the brain. Irrespective of this, drug therapy with antidepressants is the most effective way of increasing the serotonin concentration in the brain of depressive patients. Nevertheless, exercise in the fresh air, for example, is something that depressive patients are strongly advised to do.
Not least because the serotonin level in the brain can increase as a result of physical activity. In the intestine, serotonin plays a role in intestinal activity, among other things. Serotonin causes 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 the transmission of abdominal pain to the brain. Serotonin can also cause nausea and vomiting.
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