Oxytocin, a hormone produced during childbirth, provides an analgesic effect for newborns during labor and for several hours afterwards, according to a new study published in the journal Front Cell Neurosci.
Researchers at INSERM in France studied rat pups, comparing the pain response of pups less than an hour old with two-day-old pups. By measuring how long it took the rats to withdraw their tails from hot water, they found that newborn pups were about twice as resistant to pain than ones that had been alive longer.
When they injected the pups with a molecule that blocks oxytocin, however, the younger rats showed more response to pain than their older counterparts, withdrawing their tails from the water in a third of the time than they had in the previous test
"Newborn analgesia exists both in human and rodent suggesting that it is a fundamental mechanism developed and conserved through the mammalian evolution. The physiological role for the newborn analgesia is likely to prevent newborns from experiencing the pain inherent in [delivery]," conclude the researchers.