Part 2 of 2

Feedback Loop: When cortisol is present in excess amounts, a negative feedback system is set into place. High levels of cortisol inhibits the production of hypothalamic CRF which results in feedback inhibition of ACTH secretion from the pituitary. Some researchers believe that this normal feedback system breaks down when animals are exposed to chronic stress.

Catecholamines are chemical compounds derived from the amino acid tyrosine that act as neurotransmitters. High catecholamine levels in blood are considered markers for stress. Catecholamines cause physiological changes that help prepare the body for physical activity, e.g., the fight-or-flight response.

Some typical effects are increases in heart rate, blood pressure, and blood glucose levels. The catecholamines include compounds such as epinephrine (adrenaline), norepinephrine (noradrenaline), and dopamine. Epinephrine and norepinephrine are secreted by the adrenal medulla, and norepinephrine is also secreted by some nerve fibers. These substances prepare the body to meet emergencies such as cold, fatigue, and shock. Adrenaline acts as a neurotransmitter in the central nervous system and as a hormone in the blood circulation. It increases heart rate and stroke volume, dilates the pupils, and constricts arterioles in the skin and gut while dilating arterioles in leg muscles. It elevates blood sugar level by increasing the breakdown of glycogen and lipids. Noradrenaline is primarily a neurotransmitter of the peripheral sympathetic nervous system. It affects parts of the brain where attention and impulsivity are controlled. Along with epinephrine this compound effects the fight-or-flight response, activating the sympathetic nervous system to directly increase heart rate, release energy from fat, and increase muscle readiness. Epinephrine is used medically to stimulate heartbeat and to treat emphysema, bronchitis, and bronchial asthma and other allergic conditions, as well as in the treatment of the eye disease glaucoma. Dopamine is an intermediate in the synthesis of epinephrine; in addition, a deficiency of dopamine in the brain is responsible for Parkinson's disease.

Endorphins have been suggested as modulators of the so-called "runner's high" that athletes achieve with prolonged exercise. At least 20 types of endorphins are known to exist. These chemicals are produced in the brain (primarily the hypothalamus and pituitary) in response to a variety of stimuli, such as exercise, meditation, and stress. Stress and pain are the two most common factors leading to the release of endorphins. Endorphins interact with the opiate receptors in the brain to reduce our perception of pain, having a similar action to drugs such as morphine and codeine. Unlike drugs, however, activation of the opiate receptors by the body's endorphins does not lead to addiction or dependence.

In addition to decreased feelings of pain, secretion of endorphins leads to feelings of euphoria, modulation of appetite, release of sex hormones, and enhancement of the immune response. Endorphin release varies among individuals - meaning that two people who exercise at the same level or suffer the same degree of pain will not necessarily produce similar levels of endorphins. Certain foods, such as chocolate or chili peppers, can also lead to enhanced secretion of endorphins. Studies of acupuncture, massage therapy, mediation, and ultraviolet light have all been shown to stimulate endorphin secretion. Sex is also a potent trigger for endorphin release. According to some reports, laughter also releases endorphins in the brain. So besides dialating blood vessels, suppressing the production of stress hormones, and raising antibody levels in the blood, laughing also has an analgesic effect.

Serotonin is a neurotransmitter synthesised in in the central nervous system and enterochromaffin cells in the gastrointestinal tract. It is believed to play an important role in the biochemistry of depression, bipolar disorder, and anxiety. It is also believed to be influential on sexuality and appetite. Serotonin helps to fight hunger, alleviate depression and OCD, decreases pain of fibromyalgia and migranes, and promotes sleep and weight loss. It was initially identified as a vasoconstrictor substance in blood serum - hence the name "serotonin". Serotonin is synthesized from the amino acid tryptophan as 5-hydroxytryptamine and is known as 5-HT in the pharmacological field.

Serotonin taken orally does not pass the blood-brain barrier which prevents it from affecting serotonin levels in the brain. However, the amino acid tryptophan is capable of crossing the blood-brain barrier. Tryptophan is available as a dietary supplements though its efficacy is questionable. A variety of psychiatric medications affect serotonin levels, including the monoamine oxidase inhibitors (MAOIs), tricyclic antidepressants (TCAs), and the selective serotonin reuptake inhibitors (SSRIs). The MAOIs prevent the breakdown of serotonin and therefore increase its concentrations in the brain. However, MAOI therapy is associated with many adverse drug reactions and patients are at risk of hypertensive crisis triggered by foods high in tyramine and certain drugs. Tricyclic antidepressants inhibit the re-uptake of both serotonin and norepinephrine making them last longer. The newer Selective Serotonin Re-uptake Inhibitors (SSRIs) have fewer (though still numerous) side effects and fewer interactions with other drugs.

Deficiency and sometimes, excessive vitamins and minerals can lead to disturbed levels of serotonin via disrupting either the production or reuptake processes. Care must be taken in any attempt to increase serotonin levels, as a dangerous condition known as "Serotonin syndrome", a condition caused by an excess of serotonin in the brain, may result. This is especially a concern if multiple serotonergic agents interact to increase 5-HT levels - such as can happen when St Johns Wort is taken in combination with an SSRI. The effects of serotonin syndrome may progress from headaches, dizziness and vomiting, to coma and death.

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