© 2013 SNL All rights reserved REVIEW Oxytocin effects in mothers and infants during breastfeeding Oxytocin integrates the function of several body systems and exerts many effects in mothers and infants during breastfeeding. This article explains the pathways of oxytocin release and reviews how oxytocin can affect behaviour due to its parallel release into the blood circulation and the brain. Oxytocin levels are higher in the infant than in the mother and these levels are affected by mode of birth. The importance of skin-to-skin contact and its association with breastfeeding and mother-infant bonding is discussed. Kerstin Uvnäs Moberg Oxytocin – a system activator increased function of inhibitory alpha-2 3 MD, PhD xytocin, a small peptide of just nine adrenoceptors . Professor of Physiology amino acids, is normally associated The regulation of the release of oxytocin Swedish University of Agriculture O with labour and the milk ejection reflex. is complex and can be affected by different [email protected] However, oxytocin is not only a hormone types of sensory inputs, by hormones such Danielle K. Prime but also a neurotransmitter and a as oestrogen and even by the oxytocin 1,2 molecule itself. This article will focus on PhD paracrine substance in the brain . During Breastfeeding Research Associate breastfeeding it is released into the brain of four major sensory input nervous Medela AG, Baar, Switzerland both mother and infant where it induces a pathways (FIGURES 2 and 3) activated by: great variety of functional responses. 1. Sucking of the mother’s nipple, in which Through three different release pathways the sensory nerves originate in the (FIGURE 1), oxytocin functions rather like a breast. system activator and often influences the 2. Sucking in the infant, in which the release of other signalling substances such sensory nerves originate in the infant as opioids, serotonin, dopamine and oral mucosa. noradrenaline. Through these activations, 3. The presence of food in the different behavioural and physiological gastrointestinal tract, affecting vagal effects are facilitated and coordinated into sensory nerves. adaptive patterns, which are influenced by 4. Skin-to-skin contact in both mothers the type of stimuli and environmental and infants, in which the sensory nerves 3 Keywords factors . that originate in the skin respond to Through the endogenous release of oxytocin; breastfeeding; skin-to-skin; warmth, touch, stroking and light anti-stress; milk ejection; bonding oxytocin or its administration, for example pressure. by nasal spray in humans, various types of Key points socially interactive behaviours can be The mother stimulated. These include maternal and Uvnäs Moberg K., Prime D.K. Oxytocin Milk ejection effects in mothers and infants during sexual behaviours as well as the develop- 4 Oxytocin is critical for milk removal in, breastfeeding. Infant 2013; 9(6): 201-06. ment of bonding and attachment . 1. Oxytocin is released in the mother and Oxytocin stimulates well-being, it induces perhaps, its most renowned role: the milk infant during breastfeeding and skin-to- anti-stress effects, decreases sensitivity to ejection reflex. Following sucking, the skin contact. pain, decreases inflammation and release of oxytocin causes the contraction 2. Milk ejection patterns vary between stimulates processes related to growth and of myoepithelial cells in the breast pushing women. healing. In addition, repeated exposure to milk from the alveoli, through the milk 3. Oxytocin is released into circulating oxytocin may give rise to long-term effects ducts and toward the nipple. blood and brain structures, in parallel. by influencing the production or function In general, it takes around a minute of 4. Oxytocin levels are higher in the infant of other signalling systems. For example, infant sucking or stimulation with a breast than in the mother and differ with noradrenergic activity in the brain pump before milk ejection occurs5,6. mode of birth. may decrease as a consequence of the Interestingly, the milk ejection reflex can be infant VOLUME 9 ISSUE 6 2013 201 REVIEW have continuous milk ejections throughout the milk removal session. Both of these Parvocellular neurons Central oxytocin release: patterns can remove similar volumes of Axons project into brain Magnocellular neurons milk successfully, but the second scenario structures and spinal cord Central oxytocin release: Dendritic extracellular diffusion would require more time to reach that 5 Axons of same level of milk removal . Similar parvocellular neurons repeatability has been observed in Paraventricular individual infants at successive breast- nucleus (PVN) feeds14; these mother-derived patterns may explain why some infants are quick feeders Supraoptic nucleus (SON) and others take a bit more time. Axons of magnocellular Oxytocin-induced effects in the brain neurons It is not known why mothers have such varied milk ejection patterns but, since Anterior pituitary Oxytocin oxytocin is involved in so many functions, these release patterns may not only impact Capillary on milk removal. Systemic oxytocin release and its release into the brain may result in many other outcomes involving Peripheral oxytocin release: breastfeeding and mother-infant Axonal release into blood to target distant organs interactions. For example, breastfeeding in Posterior pituitary mothers is associated with physiological and psychological adaptations including: ■ Increased social interaction FIGURE 1 The release of oxytocin from the supraoptic (SON) and paraventricular (PVN) nuclei ■ Decreased anxiety of the hypothalamus. Magnocellular neurons in the SON and PVN release oxytocin centrally ■ and peripherally from the posterior pituitary, resulting in effects that include milk ejection and Decreased cortisol levels ■ uterine contraction. Parvocellular neurons, located in the PVN, project axons directly into brain Decreased blood pressure structures involved in the regulation of social interaction, anxiety, the activity of the ■ Increased gastrointestinal tract 15-17 hypothalamic-pituitary-adrenal axis, well-being and the autonomic nervous system (eg the function . amygdala, hypothalamus, anterior pituitary, nucleus accumbens, nucleus tractus solitarius and These effects are exerted in the brain but the dorsal vagal motor nucleus). are associated with circulating oxytocin levels, supporting the concept that oxytocin is released systemically and into easily conditioned and many women can birth, but there is still a strong correlation the brain in parallel, as has previously been experience spontaneous milk ejections between the amount of oxytocin released demonstrated in sheep in response to between feeds7,8 as the sight, thought, on the two occasions within individual suckling18. sound and smell of the infant (or even a women13. breast pump in pump-dependent mothers) One pulse of oxytocin is generally The infant can cause milk ejection and dripping of associated with one milk ejection and there Infants produce oxytocin too and in fact, milk from the nipples. Indeed, it is is a relationship between the amount of the production of oxytocin begins in the common that milk ejection occurs prior to oxytocin released and the number of fetus. An understanding of the infant the physical attachment of the infant or a oxytocin pulses during the first 10 minutes oxytocin system is complicated by breast pump7,9. of breastfeeding12. The number of milk difficulties in collecting repeat blood Milk ejection can be associated with ejections during breastfeeding ranges from samples and measuring circulating different sensations that vary dramatically one to 17 over a period of up to 25 oxytocin levels in the newborn. between women. These may be localised to minutes6,7. Similarly, pulsatile patterns of Nevertheless, some studies exist in which the breast such as a ‘drawing’ pain or two to 14 milk ejections are seen during a oxytocin levels have been measured in the tingling, to more systemic sensations such 15 minute breast expression5. The simil- newborn while other studies have as nausea, thirst, fainting or even mental arity between the milk ejection pattern demonstrated the release of oxytocin anxiety and depression8. resulting from breastfeeding and breast indirectly via expression of oxytocin-linked Sucking- and pumping-induced pumping is demonstrated in FIGURE 4. effect patterns. Information can also be oxytocin release has been described as Tracking an individual mother over drawn from animal experiments, as pulsatile7,10. On average, oxytocin pulses time, it appears that her pattern of milk oxytocin exerts similar effect patterns in all occur with 90-second intervals over the ejection repeats throughout the first nine mammals. first 10 minutes of breastfeeding in the first months of lactation5. If a mother has two few days after birth11,12. The amount of or three milk ejections she will continue Infant oxytocin levels are affected by the oxytocin that is released within a 10 that pattern, removing all her milk in these mode of delivery minute breastfeed is much higher at four brief episodes. Other mothers may follow a In infants born by vaginal delivery, months when compared to four days after more constant pulsing profile in that they oxytocin levels in umbilical arterial blood 202 VOLUME 9 ISSUE 6 2013 infant REVIEW were actually higher than in infants born by caesarean section: 69pg/mL Skin-to-skin contact (range 20-315pg/mL) vs 33pg/mL (range 9-195pg/mL), respectively. Mothers also had higher oxytocin