Melatonin pineal gland

Melatonin Pineal gland Sleep aid Sedation headache loss of libido. 

Melatonin. Melatonin (A/-acetyl-5-metlioxytryptaniine) [73-31-4] C 2H gN2O2(250) is secreted from the pineal gland and retina during dark periods of the vertebrate circadian rhythm (65). Melatonin regulates biological rhythms and neuroendocrine function and is formed from serotonin (5-HT). 

However, despite its enormous importance to human physiology, no pharmacological compounds targeting the components of the circadian clock system have been identified to date. There are, nevertheless, two therapeutic approaches that are currently used for treatment of circadian-related disorders - full-spectrum and bright light therapy and melatonin therapy. Melatonin is a hormone that is produced by the pineal gland in... 

Figure 22.1 Pathways projecting to and from the suprachiasmatic nucleus (SCN). Inputs from photoreceptors in the retina help to reset the circadian clock in response to changes in the light cycle. Other inputs derive from the lateral geniculate complex and the serotonergic, Raphe nuclei and help to reset the SCN in response to non-photic stimuli. Neurons in the SCN project to the hypothalamus, which has a key role in the regulation of the reproductive cycle, mood and the sleep-waking cycle. These neurons also project to the pineal gland which shows rhythmic changes in the rate of synthesis and release of the hormone, melatonin...

Figure 22.3 Possible links in the induction of circadian rhythm between daylight, the suprachiasmatic nucleus and melatonin release from the pineal gland. Some fibres in the optic nerve, projecting from the eye to the lateral geniculate nucleus (LGN) in the thalamus, innervate the suprachiasmatic nucleus (SCN) in the anterior hypothalamus, via the retinohypothalamic tract (RHT). Others project to the SCN from the LGN in the geniculohypothalamic tract (GHT). The release of melatonin into the circulation from the pineal gland (PG) is maximal at night and appears to be controlled partly by noradrenaline released from sympathetic nerves originating in the superior cervical ganglion (SCG). Melatonin receptors are found in the SCN, the removal of which dampens melatonin secretion...

Axelrod, J. 8r Wurtman, R. J. (1966). The formation, metabohsm and some actions of melatonin, a pineal gland substance. Res. Publ. Assoc. Res. Nerv. Merit. Dis. 43, 200-11. 

FIGURE 13-5 The biosynthesis and catabolism of serotonin. Note that in the pineal gland, serotonin is converted enzymatically to melatonin. 

Serotonin is an indolamine neurotransmitter, derived from the amino acid L-tryptophan. Tryptophan is converted to 5-hydroxytryptophan (5-HTP) by tryptophan hydroxylase. 5-HTP is converted to 5-hydroxytryptamine (serotonin, 5-HT) by aromatic amino acid decarboxylase. In the pineal gland, 5-HT may be further converted to /V-acetyl serotonin by 5-HT /V-acetyltransferase and then to melatonin by 5-hyroxyindole-O-methyltransferase. 5-HT is catabolized by monoamine oxidase, and the primary end metabolite is 5-hydroxyindoleacetic acid (5-HIAA). 

Nicotinic receptors are present in the pineal gland (Stankov et al. 1993). Although there appear to be no direct effects of nicotine on the release of melatonin, it indirectly reduces the accumulation of melatonin stimulated by norepinephrine. Nicotine increases circulating levels of norepinephrine and epinephrine (Pomerleau et al. 1983). 

Dietary Supplements. In the past 10 years, melatonin, available as a dietary supplement from health food stores or over the Internet, has become a popular sleep agent. Melatonin is a hormone produced by the pineal gland at peak levels during the night. It is believed to help regulate the 24 hour circadian sleep-wake cycle. 

The novel endocrine glands are the skin, gastrointestinal tract, adipose tissue, kidney (juxtaglomerular apparatus in the cortex which secretes renin that indirectly controls aldosterone secretion, via angiotensin-11), pineal gland, which secretes melatonin, and the heart (cardiac myocytes in the atria, which secrete atrial natriuretic peptide). 

HT is metabolized by the action of monoamine oxidase by a process of oxidative deamination to yield 5-hydroxyindoleacetic acid (5-HIAA). In the pineal gland, 5-HT is o-methylated to form melatonin. While the physiological importance of this transmitter in the regulation of the oestrus cycle in ferrets would appear to be established, its precise role in man is unknown. Nevertheless, it has been speculated that melatonin plays some... 

Melatonin is A-acetyl-5-methoxytryptamine, a simple derivative of serotonin. It is a natural hormone secreted by the pineal gland in the brain during the hours of darkness. It is involved in controlling the body s day-night... 

The peptide, melatonin, has been implicated in autism. Excess melatonin is thought to decrease learning, memory, attention, emotionality, motivation and pain responses (reviewed Chamberlain Herman, 1990)—all behaviours that are abnormal in autism. Melatonin, released from the pineal gland, is implicated in controlling serotonin and POMC (proopiomelanocortin) peptides, such as beta-endorphin, and an elevation may contribute to, or cause, the serotonin and opioid abnormalities (Chamberlain Herman, 1990). 

In addition to its presumed role as a neurotransmitter within the brain, serotonin is synthesized in the pineal gland, where it is a precursor for the synthesis of melatonin, a hormone that influences endocrine activity, presumably by an action within the hypothalamus. 

Reiter RJ The pineal gland and its neurohormone melatonin basic aspects, in Hormonal Modulation of Brain and Behavior. Edited by Halbreich U. Washington, DC, American Psychiatric Press [in press b)... 

Serotonin is present in a variety of sites in the brain. Its role as a neurotransmitter and its relation to the actions of drugs acting in the central nervous system are discussed in Chapters 21 and 30. Serotonin is also a precursor of melatonin in the pineal gland (Figure 16-2 ... 

Melatonin is /V-acetyl-5-methoxytryptamine (Figure 16-2), a simple methoxylated and /V-acetylated product of serotonin found in the pineal gland. It is produced and released primarily at night and has long been suspected of playing a role in diurnal cycles of animals and the sleep-wake behavior of humans. 

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