Serotonin
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Serotonin (5-hydroxytryptamine: 5-HT) is a neurotransmitter produced in the human brainstem and synthesized from L-Tryptophan, an essential amino acid. Considered a hormone, it is found in the human brain, gastrointestinal tract, whole blood, plasma and pineal gland. Serotonin provides the regulation and mediation of various physiological functions in several systems and contributes significantly to a feeling of overall well-being, calm and pleasure.
Cardiovascular System and Serotonin
Serotonin affects the cardiovascular system by regulating normal cardiovascular activity. Elevated serotonin levels induce tachycardia (rapid heart rate), increase cardiac stress and the possibility of cardiac disease. Reduced serotonin levels can result in a slowed heart rate, suppressed cardiovascular activity and heart failure.
Hemostasis and Serotonin
Serotonin levels appear to impact human hemostatis, which is the regulation of bleeding, through mechanisms such as clotting.
Gastrointestinal System and Serotonin
Serotonin affects the gastrointestinal system and approximately 95% of the body’s serotonin is found in that system, particularly within the intestinal wall. Gastrointestinal discomfort and disease such as ulcers, irritable bowel syndrome, bloody stool, diarrhea and constipation have been linked to abnormal serotonin levels found in the gastrointestinal system.
Immunity and Serotonin
Serotonin is found in components of the human immune system and appears to play a significant role in the neural functioning of the immune system.
Renal System and Serotonin
Serotonin excess is processed and excreted from the body through the kidneys. Renal damage can occur with the processing and excretion of elevated levels of serotonin over prolonged periods. Such renal complications can occur in Substance Disorders and in Serotonin Toxicity Syndrome.
Serotonin Toxicity Syndrome
Also known as Serotonin Syndrome, Serotonin Toxicity Syndrome occurs when there are extremely high levels of serotonin present during an adverse reaction to the use of substances with pro-serotonergic properties. Pro-serotonergic substances stimulate the production of serotonin and increase its physiological activity and effects. Serotonin Toxicity Syndrome typically occurs with a sudden acute onset that progresses quickly and can be fatal. Onset typically begins with the administration of a new substance or after an increased dose of an already tolerated substance with pro-serotonergic effects. Serotonin Toxicity Syndrome can be induced by the use of therapeutic medication, adverse interactions between medications or substance abuse and dependence.
Symptoms of Serotonin Toxicity Syndrome can include the following:
• tachycardia
• irregular heartbeat
• headache
• dilated pupils
• chills
• gooseflesh
• confusion
• motor tics
• loss of coordination
• restlessness
• agitation
• fever
• seizures
• unconsciousness
Serotonin Toxicity Syndrome requires emergency medical attention. With proper treatment, which includes cessation and neutralization of the offending substance, therapeutic support for the control of agitation and hypothermia and treatment of hypertension, the condition usually subsides within 24 hours.
Substances of Abuse and Dependence and Serotonin
Substances of abuse and dependence such as hallucinogens, cannabis, alcohol, opioids and stimulants affect serotonin levels. Such chemicals raise serotonin levels creating a sense of well-being, pleasure and euphoria. Further use of substances is reinforced by the immediate positive effects, however, the prolonged use of psychoactive chemicals can negatively impact the brain’s ability to produce and use serotonin. Substance-induced elevated levels of serotonin can decrease the number of serotonin receptors in the brain. Elevated levels over a prolonged period can also negatively impact the functioning of available serotonin receptors. Cessation of substance use can result in serotonin ‘deficiency’ and associated discomfort in abstinence. Symptoms of interrupted serotonin processes can appear for some time after abstinence from prolonged and/or excessive use of psychoactive substances that have elevated serotonin levels. These symptoms are found in the Prolonged Abstinence Withdrawal Syndrome (PAWS) and contribute to relapse to substance use:
• depression
• fatigue
• thought disorder
• agitation
• mental confusion
• cognitive clouding
• memory and learning impairments
• obsessive thinking
• compulsive behavior
• Impulsive behavior
Serotonin and Psychological Functioning
Serotonin levels have many psychological affects including the regulation of anxiety, mood, thoughts, libido, appetite, sleep and aggression. Pro-serotonergic medicines are used in psychiatry to treat conditions with symptoms that result from dysregulation of these. Several classes of medications target the regulation of serotonin levels. Among these are medications developed for the treatment of:
• depression
• anxiety
• agitation
• blood disorders
• migraines
• nausea
• vomiting
Antidepressants and Serotonin
Several psychiatric conditions including depression, anxiety and phobias are associated with low levels of serotonin and medications used to treat them are pro-serotonergic. Antidepressants directly affect the production of serotonin and its processes. Such medications are:
• Tricyclics (TCA’s)
• Monoamine Oxidase Inhibitors (MAO’s)
• Selective Serotonin Re-uptake Inhibitors (SSRI’s)
Tricyclics (TCAs)
Tricyclic antidepressants (TCA’s) were the first antidepressant medications developed. Tricyclics interrupt the absorption and elimination of serotonin which in turn increases available levels of serotonin in the brain. Tricyclic antidepressants include such medications as:
• Doxepin (Sinequan)
• Imipramine (Tofranil)
• Nortriptyline (Pamelor)
• Protriptyline (Vivactil)
• Trimipramine (Surmontil)
• Amitriptyline (Elavil)
• Amoxapine (Asendin)
• Desipramine (Norpramin)
Monoamine Oxidase Inhibitors (MAOs)
MAO's (Monoamine Oxidase Inhibitors) were the second generation of antidepressants developed. The use of MAO’s increases the level of serotonin in the brain by inhibiting the synthesis and elimination of neurotransmitters. MAO’s include medications such as:
• Isocarboxazid (Marplan)
• Phenelzine (Nardil)
• Tranylcypromine (Parnate)
• Moclobemide (Manerix)
• Selegiline (Emsam)
Selective Serotonin Re-uptake Inhibitors (SSRIs)
The third generation of antidepressants to become available was the Selective Serotonin Re-uptake Inhibitors (SSRI’s) such as:
• Fluoxetine (Prozac)
• Paroxetine (Paxil)
• Sertraline (Zoloft)
• Citalopram (Celexa)
• Escitalopram (Lexapro)
The use of SSRI’s interrupts the normal process (called “re-uptake”) in which serotonin is absorbed at the neural level. This interruption of the serotonin process increases the amount of available serotonin in the brain.
Effects of Increased Serotonin Levels upon Depressive Symptoms
With the increased availability of serotonin in the brain provided by antidepressants depressive symptoms such as the following are alleviated:
• fatigue
• dysphoria
• poor concentration
• anxiety
• restlessness
• agitation
• tearfulness
• fear
• memory deficits
• poor sleep
• poor appetite
• feelings of hopelessness
• irritability
• feelings of helplessness
• worry
• slowed cognition
Lifestyle Choices to Maintain Adequate Serotonin Levels
Research suggests that lifestyle choices can stimulate and maintain adequate serotonin levels that will increase a sense of well-being.
Certain foods such as legumes, soy, dairy products, chicken, fish, pork, turkey, veal and lamb provide proteins that stimulate serotonin production. Carbohydrates and chocolate also trigger the release of serotonin.
Aerobic and non-aerobic exercise, meditation, prayer, visualization and other enjoyable activities that induce relaxation, such as listening to music or engaging in hobbies, also stimulate the production of serotonin.
Adequate sleep and regular exposure to sunlight stimulate the natural production of serotonin.
Dietary supplements such as whey protein and tryptophan provide essential amino acids from which serotonin is produced.
