Serotonin, Melatonin

Serotonin

 

a neurotransmitter, derived from tryptophan, that is involved in sleep, depression, memory, and other neurological processes. (sero- serum )

a compound that occurs in the brain, intestines, and blood platelets and acts as a neurotransmitter, as well as inducing vasoconstriction and contraction of smooth muscle; 5-hydroxytryptamine (5HT)

It is popularly thought to be a contributor to feelings of well-being and happiness.

 

Approximately 90% of the human body's total serotonin is located in the enterochromaffin cells in the alimentary canal (gut), where it is used to regulate intestinal movements.^[7][8] The remainder is synthesized in serotonergic neurons of the CNS, where it has various functions. These include the regulation of mood, appetite, and sleep. Serotonin also has some cognitive functions, including memory and learning. Modulation of serotonin at synapses is thought to be a major action of several classes of pharmacological antidepressants.

Serotonin secreted from the enterochromaffin cells eventually finds its way out of tissues into the blood. There, it is actively taken up by blood platelets, which store it. When the platelets bind to a clot, they release serotonin, where it serves as a vasoconstrictor and helps to regulate hemostasis and blood clotting. Serotonin also is a growth factor for some types of cells, which may give it a role in wound healing.

Serotonin is mainly metabolized to 5-HIAA, chiefly by the liver. Metabolism involves first oxidation by monoamine oxidase to the corresponding aldehyde. This is followed by oxidation by aldehyde dehydrogenase to 5-HIAA, the indole acetic acid derivative. The latter is then excreted by the kidneys. one type of tumor, called carcinoid, sometimes secretes large amounts of serotonin into the blood, which causes various forms of the carcinoid syndrome of flushing, diarrhea, and heart problems. Because of serotonin's growth-promoting effect on cardiac myocytes, persons with serotonin-secreting carcinoid may suffer a right heart (tricuspid) valve disease syndrome, caused by proliferation of myocytes onto the valve.

In addition to animals, serotonin is found in fungi and plants.^[9] Serotonin's presence in insect venoms and plant spines serves to cause pain, which is a side effect of serotonin injection. Serotonin is produced by pathogenic amoebae, and its effect on the gut causes diarrhea. Its widespread presence in many seeds and fruits may serve to stimulate the digestive tract into expelling the seeds

 

 

Melatonin

 

a hormone secreted by the pineal gland in inverse proportion to the amount of light received by the retina, important in the regulation of biorhythms: in amphibians, it causes a lightening of the skin.

 

 A hormone derived from serotonin and produced by the pineal gland that stimulates color change in the epidermis of amphibians and reptiles and that is believed to influence estrus in mammals.

A hormone produced in the pineal gland that plays a role in regulating biological rhythms, including sleep and reproductive cycles. In many animals, melatonin also regulates the physiological effects that occur in response to seasonal changes, such as the growth of a winter coat of fur. Chemical formula: C ₁₃ H ₁₆ N ₂ O ₂ .

 

Melatonin communicates information about light to different parts of the body. It helps regulate biological rhythms and plays an important role in the reproductive cycles of many animals. In humans it is best known for helping to regulate the body's circadian sleep-wake cycle. Melatonin production is affected by light exposure to the eyes; melatonin levels rise during the night and fall during the day, becoming almost undetectable. Though it does not actually induce sleep, melatonin can have sleep-promoting effects. Experiments have shown that at high doses melatonin lowers body temperature, decreases motor activity, and increases fatigue. Melatonin production starts falling after puberty, and it can virtually disappear in the elderly, a phenomenon which could help to explain why sleep disturbances are more prevalent among older adults. Marketed as a dietary supplement and touted as a cure-all for insomnia, jet lag, and even cancer and aging, the overall effects of melatonin on human health are still largely unknown.

 

Circadian rhythm

In humans, melatonin is produced by the pineal gland, a small endocrine gland^[29] located in the center of the brain but outside the blood–brain barrier. The melatonin signal forms part of the system that regulates the sleep–wake cycle by chemically causing drowsiness and lowering the body temperature, but it is the central nervous system (specifically the suprachiasmatic nuclei, or SCN)^[29] that controls the daily cycle in most components of the paracrine and endocrine systems^[30][31] rather than the melatonin signal (as was once postulated).

Infants' melatonin levels become regular in about the third month after birth, with the highest levels measured between midnight and 08:00 (8 AM).^[32]

In humans, 90% of melatonin is cleared in a single passage through the liver, a small amount is excreted in urine,^[33] and a small amount is found in saliva.

Human melatonin production decreases as a person ages.^[34] It is believed^[who?] that as children become teenagers, the nightly schedule of melatonin release is delayed, leading to later sleeping and waking times.^[35]

Light dependence

Production of melatonin by the pineal gland is inhibited by light to the retina and permitted by darkness. Its onset each evening is called the dim-light melatonin onset (DLMO).

It is principally blue light, around 460 to 480 nm, that suppresses melatonin,^[36] proportional to the light intensity and length of exposure. Until recent history, humans in temperate climates were exposed to few hours of (blue) daylight in the winter; their fires gave predominantly yellow light. The incandescent light bulb widely used in the twentieth century produced relatively little blue light.^[37] Wearing glasses that block blue light in the hours before bedtime may decrease melatonin loss. Kayumov et al. showed that light containing only wavelengths greater than 530 nm does not suppress melatonin in bright-light conditions.^[38] Use of blue-blocking goggles the last hours before bedtime has also been advised for people who need to adjust to an earlier bedtime, as melatonin promotes sleepiness.^[39]

When used several hours before sleep according to the phase response curve for melatonin in humans, small amounts (0.3 mg^[40]) of melatonin shift the circadian clock earlier, thus promoting earlier sleep onset and morning awakening.^[41]

 

Circadian rhythm sleep disorders (CRSDs), whether chronic or transient, affect a broad range of individuals, including many elderly, those with severe visual impairments, shift workers, and jet travelers moving rapidly across many time zones. In addition, various forms of insomnia affect another large sector of the population. A feature common among CRSDs and some forms of insomnia is sensitivity to the hormone melatonin, which is secreted by the pineal gland. Accumulating evidence suggests that melatonin may regulate the circadian clock located in the suprachiasmatic nucleus (SCN) of the hypothalamus. Although the light–dark cycle is the primary signal that entrains the circadian clock to environmental cycles, exogenous melatonin has been shown to entrain the clock in individuals with no light perception and free-running circadian rhythms. Furthermore, studies have reported beneficial effects of melatonin for treatment of certain insomnias. Together, these studies suggest that melatonin may be useful for treating some insomnias and CRSDs. In these contexts, use of melatonin as a supplement has been popular in the United States. Unfortunately, the therapeutic potential of melatonin has been difficult to realize in clinical trials, possibly owing to non-specific actions of the agent and its unfavorable pharmacokinetic properties when administered orally. In an attempt to take advantage of the therapeutic opportunities available through the brain's melatonin system, researchers have developed several melatonin agonists with improved properties in comparison to melatonin. Some of these agents are now in clinical trials for treatment of insomnia or CRSDs.