Oxytocin

Oxytocin is a mammalian hormone that also acts as a neurotransmitter in the brain.

It is best known for its roles in female reproduction: it is released in large amounts after distension of the cervix and vagina during labor, and after stimulation of the nipples, facilitating birth and breastfeeding, respectively. Recent studies have begun to investigate oxytocin's role in various behaviors, including social recognition, bonding, anxiety, trust, and maternal behaviors.

Peripheral (hormonal) actions

The peripheral actions of oxytocin mainly reflect secretion from the pituitary gland.

• Letdown reflex – in lactating(breastfeeding) mothers, oxytocin acts at the mammary glands, causing milk to be 'let down' into a collecting chamber, from where it can be extracted by compressing the areola and sucking at the nipple. Sucking by the infant at the nipple is relayed by spinal nerves to the hypothalamus. The stimulation causes neurons that make oxytocin to fire action potentials in intermittent bursts; these bursts result in the secretion of pulses of oxytocin from the neurosecretory nerve terminals of the pituitary gland.
• Uterine contraction – important for cervical dilation before birth and causes contractions during the second and third stages of labor. Oxytocin release during breastfeeding causes mild but often painful uterine contractions during the first few weeks of lactation. This also serves to assist the uterus in clotting the placental attachment point postpartum.

• The relationship between oxytocin and human sexual response is unclear. At least two non-controlled studies have found increases in oxytocin at orgasm – in both men and women.<ref name="carm1987">Template:Cite journal</ref><ref name="pmid8135652">Template:Cite journal</ref> The authors of one of these studies speculated that oxytocin's effects on muscle contractibility may facilitate sperm and egg transport.<ref name="carm1987" /> Murphy et al. (1987), studying men, found that oxytocin levels were raised throughout sexual arousal and there was no acute increase at orgasm. <ref name="pmid3654918">Template:Cite journal</ref> A more recent study of men found an increase in plasma oxytocin immediately after orgasm, but only in a portion of their sample that did not reach statistical significance. The authors noted that these changes "may simply reflect contractile properties on reproductive tissue."<ref name="pmid12697037">Template:Cite journal</ref>

• Due to its similarity to vasopressin, it can reduce the excretion of urine slightly. More importantly, in several species, oxytocin can stimulate sodium excretion from the kidneys (natriuresis), and in humans, high doses of oxytocin can result in hyponatremia.

• Modulation of hypothalamic-pituitary-adrenal axis activity. Oxytocin, under certain circumstances, indirectly inhibits release of adrenocorticotropic hormone and cortisol and, in those situations, may be considered an antagonist of vasopressin.<ref name="isbn83-200-1415-8">Template:Cite book</ref>

• Sexual arousal. Oxytocin injected into the cerebrospinal fluid causes spontaneous erections in rats,<ref name="Gimpl">Template:Cite journal</ref> reflecting actions in the hypothalamus and spinal cord.

• Bonding. In the Prairie Vole, oxytocin released into the brain of the female during sexual activity is important for forming a monogamous pair bond with her sexual partner. Vasopressin appears to have a similar effect in males.<ref>Vacek M, High on Fidelity. What can voles teach us about monogamy? </ref> Oxytocin has a role in social behaviors in many species, and so it seems likely that it has similar roles in humans.

• Autism. Oxytocin may play a role in autism and may be an effective treatment for autism's repetitive and affiliative behaviors.<ref>Template:Cite journal</ref> Two related studies in adults, in 2003 and 2007, found that oxytocin decreased repetitive behaviors and improved interpretation of emotions, but these preliminary results do not necessarily apply to children.<ref>Template:Cite journal</ref>

• According to some studies in animals, oxytocin inhibits the development of tolerance to various addictive drugs and reduces withdrawal symptoms.<ref name="pmid9924746">Template:Cite journal</ref>

• Preparing fetal neurons for delivery. Crossing the placenta, maternal oxytocin reaches the fetal brain and induces a switch in the action of neurotransmitter GABA from excitatory to inhibitory on fetal cortical neurons. This silences the fetal brain for the period of delivery and reduces its vulnerability to hypoxic damage.<ref name="pmid17170309">Template:Cite journal</ref>

• Certain learning and memory functions are impaired by centrally administered oxytocin.<ref name="Gimpl" />. Also, systemic oxytocin administration can impair memory retrieval in certain aversive memory tasks.<ref name="pmid16997585">Template:Cite journal</ref>

• MDMA (ecstasy) may increase feelings of love, empathy and connection to others by stimulating oxytocin activity via activation of serotonin 5-HT1A receptors, if initial studies in animals apply to humans.<ref name="pmid17383105">Template:Cite journal</ref>

Drug forms

Synthetic oxytocin is sold as medication under the trade names Pitocin and Syntocinon and also as generic oxytocin. Oxytocin is destroyed in the gastrointestinal tract, and therefore must be administered by injection or as nasal spray.

References

• Original content of the article was taken from Wikipedia.org

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External links

• Peaceful Touch - A healthy touch approach for children
• New Scientist -'Cuddle chemical' could treat mental illness (14 May 2008)
• Caldwell, H.K. and Young, W.S., III. Oxytocin and Vasopressin: Genetics and Behavioral Implications in Lim, R. (ed.) Handbook of Neurochemistry and Molecular Neurobiology, 3rd edition, Springer, New York, pp. 573-607, 2006. 320kb PDF
• NewScientist.com - 'Release of Oxytocin due to penetrative sex reduces stress and neurotic tendencies', New Scientist (January 26, 2006)
• Oxytocin.org - 'I get a kick out of you: Scientists are finding that, after all, love really is down to a chemical addiction between people', The Economist (February 12, 2004)
• SMH.com.au - 'To sniff at danger: Inhalable oxytocin could become a cure for social fears', Boston Globe (January 12, 2006)
• Hug the Monkey - A weblog devoted entirely to oxytocin
• A Neurophysiologic Model of the Circuitry of Oxytocin in Arousal, Female Distress and Depression - Rainer K. Liedtke, MD

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