OXYTOCIN

Oxytocin is a mammalian hormone that also acts as a neurotransmitter in the brain. In humans, it is thought to be released during hugging, touching, and orgams in both sexes. In the brain, oxytocin is involved in social recognition and bonding, and may be involved in the formation of trust between people and generosity.

In women, 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. Synthetic oxytocin is sold as medication under the trade names Pitocin and Syntocinon as well as generic oxytocin.

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 amygdale, ventromedial hypothalamus, septum and brainstem.

·           Sexual arousal. Oxytocin injected into the cerebrospinal fluid causes spontaneous erections in rats, 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. 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.

·           Autism. A 2003 study found a decrease in autism spectrum repetitive behaviors when oxytocin was administered intravenously. A 2007 study reported that oxytocin helped autistic adults retain the ability to evaluate the emotional significance of speech intonation.

·           Maternal behavior. Sheep and rat females given oxytocin antagonists after giving birth do not exhibit typical maternal behavior. By contrast, virgin female sheep show maternal behavior towards foreign lambs upon cerebrospinal fluid infusion of oxytocin, which they would not do otherwise.

·           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.[18] Nasally administered oxytocin has also been reported to reduce fear, possibly by inhibiting the amygdale (which is thought to be responsible for fear responses). There is no conclusive evidence for access of oxytocin to the brain through intranasal administration, however.

·           Affecting generosity by increasing empathy during perspective taking. In a neuroeconomics experiment, intranasal oxytocin increased generosity in the Ultimatum Game by 80% but has no effect in the Dictator Game that measures altruism. Perspective-taking is not required in the Dictator Game, but the researchers in this experimental explicitly induced perspective-taking in the Ultimatum Game by not identifying to participants which role they would be in.

·           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.

·           Certain learning and memory functions are impaired by centrally administered oxytocin. Also, systemic oxytocin administration can impair memory retrieval in certain aversive memory tasks.

·           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.