How does a baby’s cry trigger your milk to flow? This is a question parents have had for decades. In a study released this week, Researchers at NYU Grossman School of Medicine have made a groundbreaking discovery about the connection between a newborn’s cry and the release of breast milk in mothers. Their study, published in the journal Nature, reveals that the sound of a baby’s cry triggers the release of oxytocin, a brain chemical responsible for controlling milk production. This flood of hormones lasts for approximately five minutes, allowing mothers to feed their babies until they are satisfied.
For centuries, it has been observed that a baby’s cry stimulates the release of breast milk in mothers. However, the mechanisms behind this phenomenon were not well understood until now. The researchers found that when a mouse pup cries, sound information is transmitted to a specific area of its mother’s brain called the posterior intralaminar nucleus of the thalamus (PIL). From there, signals are sent to oxytocin-releasing neurons in the hypothalamus, which controls hormone activity.
Normally, these neurons are locked down to prevent unnecessary milk release. However, after 30 seconds of continuous crying, signals from the PIL overpower the inhibitory proteins and trigger oxytocin release.
The study also revealed that the oxytocin boost only occurs in mother mice and not in females who have never given birth. Furthermore, the mother’s brain only responds to her pups’ cries and not computer-generated tones designed to mimic natural cries.
According to Habon Issa, a graduate student at NYU Langone Health and study co-lead author, this research provides the first description of how sensory experiences like hearing directly activate oxytocin neurons in mothers. The researchers used a molecular sensor called iTango to measure actual oxytocin release in real time, a significant improvement over previous indirect measurement methods.
The team also investigated how this brain circuitry affects parenting behavior. When the communication between the PIL and oxytocin neurons was chemically blocked, mother mice eventually stopped fetching their young when they strayed or were removed from the nest. However, when the system was turned back on, the mothers pushed through their fatigue and continued caring for the infants.
Study senior author Robert C. Froemke, PhD, suggests that understanding how the oxytocin system works in our own species could lead to new interventions to help human mothers who struggle with breastfeeding.
It is important to note that the study only measured hormone release, not lactation itself. Funding for the research was provided by National Institutes of Health grants and other sources.
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