What is oxytocin?
Oxytocin is a peptide hormone (and also a neurotransmitter – messenger chemical between nerve cells) produced in our brains – namely the hypothalamus.
It is widely present in many animals, and it is present in us humans too, and generally in greater amounts in biological females than males. It is involved in influencing many forms of behaviour, childbirth and breastfeeding.
Oxytocin exerts its effect after being released from the rear end of the pituitary gland and stimulating receptors in many areas of the brain as well as many other parts of the body.
Research studies of the effects of oxytocin in people have been associative, meaning inconclusive in many aspects, apart from breast feeding and labour. But animal studies and accumulating research into complex realms of human hormones and behaviour seem to indicate oxytocin’s involvement in relationship building, tendency to form social constructs, and behaviour regulation in general, hence its role in psychiatric and behavioural disorders.
Let’s start with what we know for sure about oxytocin.
Childbirth
Oxytocin allows labour to occur by causing contractions of the uterus. It also stimulates the increase in the production for prostaglandins (more chemical messengers), which also increase contractions of the uterus. Synthetic forms of oxytocin can be given to mothers to increase the magnitude and frequency of contractions.
Beyond the labour process, oxytocin has been associated with the formation of mother and infant bonds.
Breastfeeding
The suckling behaviour of infants on the breasts of mothers signals to the brain to release oxytocin. This increased level of oxytocin in pulses causes release of milk from the milk ducts and out to the nipple. The increased level of oxytocin during this period also is hypothesised to solidify the mother and baby’s bond.
Stress Response
Oxytocin is one of the key chemical messengers which regulate stress. It reduces cortisol levels, reduces the fight-or-flight responses, and is linked to promoting seeking of social comfort, which further increases oxytocin levels creating a positive feedback loop.
Hypotheses in Bonding and Mating Behaviour in Humans
“The scientific tale of love begins innocently enough with voles. The prairie vole is a sociable rodent, found in the woodlands of Europe and Asia, one of the only 3% of mammal species that appear to form monogamous relationships. Mating between prairie voles is a tremendous effort which takes almost 24 h, following which they bond for life. They prefer to spend time with each other, groom each other for hours and at end, nest together. They avoid meeting other potential mates.
However, another vole, a close relative called the montane vole, has no interest in partnership beyond one-night-stand sex. What is intriguing is that this major difference in behavior in two vole species, which are more than 99% genetically alike, is just because of a handful of genes, which affect their endocrine function.
The details of the vole story are fascinating. When prairie voles have sex, two posterior pituitary hormones, oxytocin and vasopressin, are released. If the release of these hormones is blocked, prairie-voles’ sex becomes a fleeting affair, similar to that normally enjoyed by their montane cousins. Conversely, if prairie voles are given an injection of the hormones, but prevented from having sex, they will still form a preference for their chosen partner.
Does this mean that an injection of oxytocin can make prairie voles fall in love? Or that it encourages monogamy? A clue to what is happening, and how these results might bear on human behavior, was found when oxytocin was administered to the montane vole. It was found to make no difference. It turned out that the monogamous prairie vole has receptors for oxytocin and vasopressin in brain regions associated with reward and reinforcement, whereas the philandering montane vole does not.”(1)
Due to humans having more agency than animals and it is very unethical to knock out parts of our brain for experimental purposes, it is quite difficult to definitely prove a causative effect of oxytocin and its effects in human relationships.
More details regarding oxytocin will be continued in Part 2.
Reference
1. Magon, N. and Kalra, S. (2011) ‘The orgasmic history of oxytocin: Love, Lust, and Labor’, Indian Journal of Endocrinology and Metabolism, 15(7), p. 156. doi:10.4103/2230-8210.84851.
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