Oxytocin is a hormone that plays a vital role in the reproductive system. In the brain, it is involved in behaviors including social bonding. A protein called the oxytocin receptor allows cells to recognize this hormone and respond to it. This receptor can be found in some areas of the mammary gland and uterus, and in several brain structures.
Steroid hormones help regulate the expression of the gene that encodes the oxytocin receptor. The presence of estrogen, for example, increases gene expression, and thus the overall level of oxytocin receptors in a cell. Oxytocin has many effects during pregnancy, such as uterine contraction, and afterward, such as the release of milk. The levels of steroids assist in determining the presence of oxytocin receptors during these times, allowing the uterus and mammary glands to respond to it.
Some neurons release oxytocin, and receptors that are present in brain structures like the brain stem, nucleus accumbens, and amygdala allow the brain to react to this hormone. It is involved in maternal behaviors, social bonding, and sexual behavior. Variations in the gene that codes for it could explain some differences in these behaviors between individuals.
One study investigated how differences in the oxytocin receptor gene could impact prosocial behavior. The researchers found a link between the gene and participants' behavior in a game that involved giving money. Some participants had a copy of the gene that encouraged more receptors to be created. These individuals tended to give more money to the other player in the game, on average.
Other individuals in the study had a copy of the receptor gene that encouraged gene suppression. This would have the result of not creating as many receptors for oxytocin, and a diminished response to the hormone. Individuals with this gene variant tended to give less money to the other player in the game. The study shows that changes in how this receptor is expressed can have a significant impact on social functioning.
The disease autism is marked by antisocial behavior, in addition to a number of other symptoms. The expression of the oxytocin receptor gene may play a role in this behavior. Individuals with autism have shown to have a lower expression of this receptor than non-autistic people. This difference could explain at least some of the changes in social behavior seen in autism. The oxytocin receptor determines how people respond to oxytocin, and this influences not only reproductive processes, but complex social interactions as well.