Posted by Phillipa on May 6, 2007, at 19:17:35
In reply to Re: oxycotin and empathy? » devunea, posted by Phillipa on May 6, 2007, at 19:09:14
Here's one. Love Phillipa
[edit] Peripheral (hormonal) actions
The peripheral actions of oxytocin mainly reflect secretion from the pituitary gland. (See oxytocin receptor for more detail on its action.)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 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. However, in knockout mice lacking the oxytocin receptor, reproductive behavior and parturition is normal.[1]
Oxytocin is secreted into the blood at orgasm – in both males and females.[2] In males, oxytocin may facilitate sperm transport in ejaculation.
Due to its similarity to vasopressin, it can reduce the excretion of urine slightly. More important, in several species, oxytocin can stimulate sodium excretion from the kidneys (natriuresis), and in humans, high doses of oxytocin can result in hyponatremia.
Oxytocin and oxytocin receptors are also found in the heart in some rodents, and the hormone may play a role in the embryonal development of the heart by promoting cardiomyocyte differentiation. [3][4] However, the absence of either oxytocin or its receptor in knockout mice has not been reported to produce cardiac insufficiencies.[1][edit] Actions of oxytocin within the brain
Oxytocin secreted from the pituitary gland cannot re-enter the brain because of the blood-brain barrier. Instead, the behavioral effects of oxytocin are thought to reflect release from centrally-projecting oxytocin neurons, different from those that project to the pituitary gland. Oxytocin receptors are expressed by neurons in many parts of the brain and spinal cord, including the amygdala, ventromedial hypothalamus, septum and brainstem.Sexual arousal. Oxytocin injected into the cerebrospinal fluid causes spontaneous erections in rats,[5] 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 [6]. In people, plasma concentrations of oxytocin have been reported to be higher amongst people who claim to be falling in love. Oxytocin has a role in social behaviors in many species, and so it seems likely that it has similar roles in humans. It has been suggested that deficiencies in oxytocin pathways in the brain might be a feature of autism.
Maternal behavior. Sheep and rat females given oxytocin antagonists after giving birth do not exhibit typical maternal behavior. By contrast, virgin sheep females show maternal behavior towards foreign lambs upon cerebrospinal fluid infusion of oxytocin, which they would not do otherwise. [7]
Various anti-stress functions. Oxytocin reduces blood pressure and cortisol levels, increasing tolerance to pain, and reducing anxiety. Oxytocin may play a role in encouraging "tend and befriend", as opposed to "fight or flight", behavior, in response to stress.
Increasing trust and reducing fear. In a risky investment game, experimental subjects given nasally administered oxytocin displayed "the highest level of trust" twice as often as the control group. Subjects who were told that they were interacting with a computer showed no such reaction, leading to the conclusion that oxytocin was not merely affecting risk-aversion.[8] Nasally-administered oxytocin has also been reported to reduce fear, possibly by inhibiting the amygdala (which is thought to be responsible for fear responses).[9] There is no conclusive evidence for access of oxytocin to the brain through intranasal administration, however.
According to some studies in animals, oxytocin inhibits the development of tolerance to various addictive drugs (opiates, cocaine, alcohol) and reduces withdrawal symptoms.[10]
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.[11]
Certain learning and memory functions are impaired by centrally-administered oxytocin.[5][edit] Uses
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. Oxytocin has a half-life of typically about three minutes in the blood. Oxytocin given intravenously does not enter the brain in significant quantities - it is excluded from the brain by the blood-brain barrier. Drugs administered by nasal spray are thought to have better access to the CNS. An oxytocin nasal spray has been used to stimulate breastfeeding.Injected oxytocin analogues are used to induce labour and support labour in case of non-progression of parturition. It has largely replaced ergotamine as the principal agent to increase uterine tone in acute postpartum haemorrhage. Oxytocin is also used in veterinary medicine to facilitate birth and to increase milk production. The tocolytic agent atosiban (Tractocile®) acts as an antagonist of oxytocin receptors; this drug is registered in many countries to suppress premature labour between 24 and 33 weeks of gestation. It has fewer side-effects than drugs previously used for this purpose (ritodrine, salbutamol and terbutaline).
Some have suggested that the trust-inducing property of oxytocin might help those who suffer from social anxieties, while others have noted the potential for abuse with confidence tricks.
[edit] Potential adverse reactions
Oxytocin is relatively safe when used at recommended doses. Potential side effects include:[citation needed]Central nervous system: Subarachnoid hemorrhage, seizures.
Cardiovascular: Increased heart rate, blood pressure, systemic venous return, cardiac output, and arrhythmias.
Genitourinary: Impaired uterine blood flow, pelvic hematoma, tetanic uterine contractions, uterine rupture, postpartum hemorrhage.[edit] Evolution
Virtually all vertebrates have an oxytocin-like nonapeptide hormone that supports reproductive functions and a vasopressin-like nonapeptide hormone involved in water regulation. The two genes are always located close to each other (less than 15,000 bases apart) on the same chromosome and are transcribed in opposite directions. It is thought that the two genes resulted from a gene duplication event; the ancestral gene is estimated to be about 500 million years old and is found in cyclostomes (modern members of the Agnatha).[5]
[edit] See also
Ergometrine Maleate
[edit] References
^ a b Takayanagi Y et al. (2005) Pervasive
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