Postpartum Oxytocin – Bonding with Mothers and Babies
A new study by Valsamma Eapen and colleagues from University of New South Wales, Sydney, Australia found that women with low oxytocinlevels in the postpartum have a history of bad mother-to-daughter bonding. The study is perhaps the first to show that women with reduced levels of oxytocin in the postpartum have higher subjective ratings and reported difficulties in bonding with their own mothers.
As previous research indicates that the ‘love hormone’ oxytocin is essential for the establishment of early bonding, the study suggests that mothers with low postpartum oxytocin may also struggle to bond with their own children.
Oxytocin is a peptide hormone and neuropeptide produced in the hypothalamus and released by the posterior pituitary. The uterine-contracting properties of the principle that would later be named oxytocin were discovered by British pharmacologist Henry Hallett Dale in 1906.
Figure 1. Peripheral effects of central oxytocin release during childbirth and lactation. The neuropeptide oxytocin is mainly produced by magnocellular neurons in the paraventricular nucleus (PVN) and the supraoptic nucleus (SON) of the hypothalamus. Axons of these neurons terminate in the neurohypophysis, where oxytocin is secreted – in pulses – into the blood. Mechanoreceptors in the nipple (activated by the suckling newborn) and the cervix (cf. Ferguson reflex) create a positive sensory feedback loop, which leads to the additional release of oxytocin in the brain. Oxytocinergic neurons in the hypothalamus also release oxytocin to other brain areas via axonal transport and via dendritic release (not shown). NAc, Nucleus accumbens; PFC, Prefrontal cortex; SCN, Suprachiasmatic nucleus; BNST, Bed nucleus of the stria terminalis. Created with BioRender.com. From: ‘The Role of Oxytocin and the Effect of Stress During Childbirth: Neurobiological Basics and Implications for Mother and Child’, by Michael H. Walter, Harald Abele and Claudia F. Plappert; Front. Endocrinol., 27 October 2021 Sec. Neuroendocrine Science, https://doi.org/10.3389/fendo.2021.742236, Public domain.
It plays a role in social bonding, reproduction, childbirth, and the period after childbirth. Oxytocin is released into the bloodstream as a hormone in response to sexual activity and during labour. In either form, oxytocin stimulates uterine contractions to speed up the process of childbirth. In its natural form, it also plays a role in bonding with the baby and milk production.
According to the authors, “the immediate postpartum results show that what you experienced from parenting – these formative experiences – are critical in wiring your response to the oxytocin hormone”.
Since early exposure to dysfunctional parenting may contribute to childhood and later-onset mental disorders, the authors suggests that improving maternal sensitivity and bonding within the early period can alter the trajectory of development through programming of the infant oxytocinergic system. This may facilitate secure attachment and emotional resilience, mediated by neural receptivity to oxytocin release.
A 2019 study identified the human endogenous oxytocin system, which is known for its critical role in mammalian sociality as a system sensitive to its early environment and subject to epigenetic change. This is based on a previous animal work suggesting that early parental care is associated with changes in DNA methylation of conserved regulatory sites within the oxytocin receptor gene (OXTRm).
The authors demonstrate that the OXTRm is dynamic in infancy and its change is predicted by maternal engagement and reflective of behavioral temperament. Thus, the authors found that epigenetic changes had occurred in infant’s DNA, and that this change was predicted by the quality of the mother’s involvement in the play session. If mothers were particularly involved in the game with their children, there was a greater reduction in DNA methylation of the oxytocin receptor gene one year later. Decreased DNA methylation in this region has previously been associated with increased expression of the oxytocin receptor gene. Thus, greater maternal involvement seems to have the potential to upregulate the oxytocin system in human offspring.
Importantly, the authors also found that the DNA methylation levels reflected infant temperament, which was reported to us by the parents. The children with higher methylation levels at 18-months, and presumably lower levels of oxytocin receptor, were also more temperamental and less well balanced. Thus, the authors provide evidence for an early window of environmental epigenetic regulation of the oxytocin system, facilitating the emergence of individual differences in human behavior.
A 2019 systematic review explores the role of oxytocin in the context of establishing social affiliative bonds during early parental care. The reviewed studies used mother-infant and/or father-infant play and skin-to-skin contact between maternal-infant and paternal-infant dyads to examine the oxytocin role in early life bonding and parenting processes. Studies showed a positive correlation between parent-infant contact and oxytocin levels in infancy period.
Increased maternal oxytocin levels were significantly related to more affectionate contact behaviors in mothers following mother-infant contact, synchrony, and engagement. Oxytocin levels significantly increased in infants, mothers and fathers during skin-to-skin contact and parents with higher oxytocin levels exhibited more synchrony and responsiveness in their infant interactions.
A 2021 review article discusses some major mechanisms and the role of oxytocin in mother–infant bonding. The authors of this review specify that most of what we know about the role of oxytocin in maternal behaviors comes from animal studies, mainly from findings in rodents and sheep.
Thus, research in rodents has revealed that the initiation of the mother–infant bond by recognition of the young is regulated by an interaction between oxytocin, estrogen, and prolactin in the anterior hypothalamus and the stria terminalis, which connects the hypothalamus with the amygdala. Furthermore, these nuclei interact with the dopaminergic reward system, which in turn controls maternal motivation. Furthermore, as per another recent study by Numan and Young the projections from the olfactory system (olfactory recognition of the young) and the amygdala (responsible for the evaluation of emotional valence) are crucial for the initiation of the bond. The oxytocin required for these processes stems from oxytocinergic projections from the PVN to the anterior hypothalamus, which are activated by the Ferguson reflex and nipple stimulation.
Of note, contrary to the adult brain, the blood–brain barrier of the fetus is permeable for peripheral oxytocin from its mother’s circulatory system. In rodents it was shown that a systemic administration of oxytocin to the dam during birth has a long-term impact on the behavior of the pups.
In conclusion, the authors of this review postulate that oxytocin influences a large bandwidth of basic biological functions of human social behavior, including recognition, trust and empathy. By lying the basis for reproductive pair-bonds it ensures our species’ survival. It does so by directly supporting childbirth and lactation and by affecting the emotional processes of parental care, pair bonding and social interactions by changes in the physiology and anatomy of maternal brains.