California mouse
The California mouse was the perfect animal model for research on BPA exposure and parenting behavior, because the species is monogamous and bi-parental.
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A study on mice suggests that the chemical Bisphenol A, or BPA, could have adverse effects on parenting behavior.

BPA has become one of the most visible and controversial of the thousands of chemicals known to affect human bodies and minds. BPA is an endocrine disrupting chemical that has been implicated in a host of adverse health effects, including cancers, reproductive deficiencies in males and females, neural behavior deficits and immunological problems.

BPA’s connection to parenting behavior is less widely known, according to Cheryl Rosenfeld, a biomedical sciences professor at the College of Veterinary Medicine at the University of Missouri and one of the study’s lead authors.

Rosenfeld focused her work on the California mouse, because, unlike regular laboratory mice and rodents, they exhibit monogamy and are bi-parental. Past studies have looked only at maternal behaviors, Rosenfeld explains, because in laboratory mice and rats, the dad does not display any parental investment.

But for the California mouse, dad cares — and the survival of his offspring is dependent upon receiving parental care from both parents, Rosenfeld says.

Like other studies with laboratory mice and rats, Rosenfeld found that developmental exposure to Bisphenol A reduced maternal investment. That is, time spent nursing and time spent in the nest decreased if the mother was exposed to BPA.

Likewise — and this is what is novel, Rosenfeld says — the study found that the dads who were also exposed to Bisphenol A spent less time in the nest with their pups. If both parents were developmentally exposed to BPA, both reduced their parental investment.

Even more intriguing, Rosenfeld says, is this: Females who were not exposed to BPA, but who were paired with males who had been exposed, still reduced their parental investment.

“That was quite surprising to us,” Rosenfeld says. “Because the mother was a control, she obviously could engage in normal parental behaviors — but it was almost as if she could sense the compromised state of her partner and therefore she was going to reduce her parental investment in his offspring.”

It seemed to Rosenfeld that the control mother was thinking, "‘This guy’s not the best partner, so what if I get a better one? I want to invest in those offspring, so I'm going to save some of my energy resources for subsequent generations.’" California mice are monogamous, but, in the wild, if the partner dies, they will pair up again with another male or female.

Rosenfeld says she was surprised to find that paternal behaviors, like maternal behaviors, are vulnerable to endocrine disrupting chemicals.

“This is what's unique, because nobody has looked at how extrinsic factors like endocrine disruptors, paternal diet and stress could affect the male’s parental investment,” she explains. “We need to start thinking about how those findings might relate to humans, because there has not been a single study to date that has looked at how Bisphenol A, or any [endocrine disrupting chemical] exposure, can affect parenting behavior in humans. And, to me, the long-standing consequences of having reduced parental care are incredibly important.”

In humans, parenting behavior has to do a lot with culture and socioeconomics, but when it comes down to it, we are all guided by what are called neuropeptide hormones in the brain, Rosenfeld says.

“When a woman gives birth, she has a surge of a hormone called oxytocin. That lets the milk down in the breast and then the infant can feed,” she explains. “But it also solidifies the maternal-infant bond. And it is now clear that dads who have just had a son or a daughter born also get a surge of oxytocin. The same thing happens in our animal models.”

If the release of hormones like oxytocin gets disrupted by chemicals like BPA, then perhaps the bonding is interfered with in humans as it is in mice, Rosenfeld theorizes. And BPA is just one of many chemicals that have endocrine disrupting properties.

“I think we need to look at other chemicals, including heavy metals, air pollutants, nanoparticles — which have become very prevalent now in our environment, as well — and decide if they affect maternal and paternal behaviors,” Rosenfeld concludes.

This article is based on an interview that aired on PRI’s Living on Earth with Steve Curwood.

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