Hormone responsible for mother's nurturing trait, study proves

Rosie Brown has helped prove which hormone is responsible for the nurturing link between a mum and her baby. Photo / Supplied

The same hormone that stimulates milk production also helps establish the nurturing link between mother and baby, new research has found.

The study, by University of Otago researchers, has established for the first time that the hormone prolactin, best known for its role enabling milk production, establishes and maintains the normal parental care that ensures the survival of offspring.

The research team at the university's Centre for Neuroendocrinology deleted targeted prolactin receptors in the preoptic area of the brains of adult female mice.

Study co-author Dr Rosie Brown said the team observed that mice without prolactin receptors were able to get pregnant and give birth normally, but abandoned their litters about 24 hours after birth.

The researchers found that signalling by the hormone prolactin to its receptors in a specific brain region was essential for mothers to show vitally important maternal nurturing behaviour towards their young.

"Our findings establish a critical role for prolactin for more than simply milk production. This work is the first to show this hormone is a literal life saver in that it establishes and maintains the normal parental care that ensures offspring survival," Brown said.

"Prior studies suggested prolactin might alter the timing of when a virgin animal shows maternal nursing behaviour. Our study is the first one that has managed to finely manipulate the expression of the prolactin receptor gene in just a region of the brain and then look at the mother's behaviour during pregnancy and lactation.

"Unlike previous studies, our data shows that prolactin plays an essential role, not just in the timing of behaviour but in its continued display, and therefore the survival of offspring."

Disruptions in the ability of prolactin to communicate in the brain could lead to problems for mothers establishing a bond with their baby. This may in part explain issues with some animal species abandoning their young, she said.

This work was supported by a Health Research Council of New Zealand grant and a Marsden Grant from the Royal Society of New Zealand and has been published in the international journal PNAS.