Oxytocin acts both as a hormone and a neurotransmitter in the brain. The primary effects of oxytocin are uterine contraction and facilitating milk production in lactating mothers. It is used to induce labor and to aid milk production in breast-feeding mothers. Due to its structural similarity to vasopressin, oxytocin can reduce the production of urine slightly and in some species it can stimulate sodium excretion by the kidneys. Under certain circumstances, it can inhibit the release of adrenocorticotropic hormone and cortisol indirectly. In the brain, oxytocin is associated with sexual arousal and pair bonding with sexual mates in females. Oxytocin crosses the placenta and enters the brain of the fetus where it induces a switch in the effect of GABA from excitatory to inhibitory. This silences the fetal brain and reduces its vulnerability to hypoxic damage during birth. After birth, oxytocin appears to be responsible for maternal behavior. Oxytocin is also plays a role in the social behaviors of many species; in humans it appears to increase trust, reduce fear and increase empathy. Autistic child have been found to have significantly lower levels of oxytocin in their blood. Administered intravenously, oxytocin decreases repetitive behaviors and helps autistic adults to evaluate the emotional significance of speech intonation. Breathnach F. and Geary M., Semin. Perinatol., 33, 82 (2009); Yamasue H.;et al., Psychiatry Clin. Neurosci., 63, 129 (2009); Mahía J; et al., Eur. J. Neurosci., 29, 1440 (2009); van Leengoed E; et al., J. Endocrinol., 112, 275 (1987).
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