Key takeaways
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Neural circuits for maternal oxytocin release induced by infant crying
Summary
Oxytocin is a neuropeptide important for maternal physiology and infant care, including childbirth and milk ejection during lactation. Sucking triggers the release of oxytocin, but other sensory cues (specifically infant crying) can increase oxytocin levels in new human mothers indicating that crying can activate hypothalamic oxytocin neurons.
Here we describe a neural circuit that directs auditory information about infant vocalizations to mouse oxytocin neurons. We performed electrophysiological recordings and in vivo photometry of oxytocin neurons identified in awake maternal mice presented with pup calls. We found that oxytocin neurons responded to pup vocalizations, but not pure tones, via input from the posterior intralaminar thalamus , and that repetitive thalamic stimulation induced long-lasting disinhibition of oxytocin neurons. This circuit activates central oxytocin release and maternal behavior in response to calls, providing a mechanism for integration of offspring sensory signals into maternal endocrine networks to ensure modulation of brain state for efficient rearing.
Comments ( Health News )
Many new mothers know that when their newborn cries, they release milk. Now, animal research reveals a newly discovered brain circuit that may explain why this happens.
This new study showed that when a baby mouse begins to cry, the sound information travels to an area of its mother’s brain called the posterior intralaminar nucleus of the thalamus (PIL). This then sends signals to brain cells (neurons) that release oxytocin in the hypothalamus, which is a control center for hormonal activity.
While most of the time, these hypothalamus neurons are kept in check by proteins that act as gatekeepers to prevent milk wastage, after 30 seconds of continuous crying, signals from the posterior intralaminar nucleus of the thalamus (PIL) were found to ) these inhibitory proteins accumulated and dominated, triggering the release of oxytocin.
"Our findings uncover how a crying baby primes his mother’s brain to prepare her body for breastfeeding," said study co-senior author Habon Issa, a graduate student at NYU Langone Health in New York City. "Without such preparation, there may be a delay of several minutes between sucking and milk flow, which could cause frustration for the baby and stress for the parents."
The increase in oxytocin only occurs in mother mice and not in females that have never given birth. And the mothers’ brain circuits responded only to their puppy’s sounds and not to computer-generated tones designed to mimic natural cries.
Issa said the study shows how sensory experiences like hearing directly activate oxytocin neurons in mothers; However, animal research does not always produce results in humans. To study this, the scientists used a relatively new type of molecular sensor called iTango. This measured the actual release of oxytocin from brain cells in real time. Without that, researchers previously could only take indirect measurements using indicators because the hormone is small and degrades quickly.
In this study, the research team examined brain cell activity in dozens of female mice. They then tracked how sound information travels through different areas of the brain to trigger milk flow. The team also looked at how brain circuitry affects parenting behavior.
Mothers usually quickly retrieved their pups when they wandered away from the nest, no matter how many times they had to do so, Issa said.
But when the researchers chemically blocked PIL’s communication with oxytocin neurons, the mice eventually got tired and stopped searching for their pups. They once again began searching for and caring for their young after the PIL system was turned back on.
"These results suggest that the brain circuit triggered by crying is not only important for nursing behavior, but also for maintaining the mother’s attention over time and promoting effective care of her offspring even when she is exhausted," said the study’s senior author, Robert Froemke, a professor of genetics in the department of neuroscience and physiology at New York University, Langone, in a university news release.
Learning how oxytocin works may offer new ways to help human mothers who want to breastfeed but have difficulty doing so, Froemke said. She cautioned that the researchers did not measure breastfeeding itself, only the release of hormones that trigger it.
The findings were published in the journal Nature . Funding for the study was provided by the U.S. National Institutes of Health, the Natural Sciences and Engineering Research Council of Canada, and a Howard Hughes Medical Institute Faculty Grant.
What does this mean
New animal research reveals that a special brain circuit triggers the release of breast milk after a puppy cries.
