February 17, 2010

Babies on the Brain

Just being around youngsters helps rodents grow new neurons

By Catherine O’Neill Grace

“We specifically found that new brain cells were produced as a function of the adoptive female showing parental behavior,” says Robert Bridges. Photo: Andrew Cunningham

It appears that just being around babies is enough to make you act like a mom—at least if you’re a female rat. A study conducted at the Cummings School of Veterinary Medicine has shown that nulliparous rats—animals that had never given birth or had any experience with young—exposed to foster pups very quickly exhibited typical maternal behaviors. But more than their behavior changed—their brains did, too. It turns out they grew new neurons, or nerve cells.

Scientists already knew that exposure to young can stimulate maternal behavior in rats, mice, hamsters, monkeys—and humans. The creation of new neurons, or neurogenesis, has also been shown during pregnancy and lactation in rodents. The big breakthrough in the Tufts study is that the neurological change happened in the absence of pregnancy or nursing.

The National Institutes of Health-funded study, conducted by biomedical researchers Miyako Furuta, a postdoctoral fellow who currently is a research associate at Toyko University, and Robert Bridges, who heads the reproduction and neurobiology section at the Cummings School, was published in the December 2009 issue of Brain Research Bulletin.

“We specifically found that new brain cells were produced as a function of the adoptive female showing parental behavior,” says Bridges. The adoptive moms started crouching over the pups, grouping them or carrying them back to the nest. On average, it took about a week of daily exposure to the babies for the rats to begin acting like mothers.

The researchers found that the new neurons grew in the area of the brain known as the subventricular zone, which is involved in the production of cells that can affect odor recognition. “New neurons produced in this brain region migrate to the olfactory bulb where they can become integrated into the olfactory neural network,” says Bridges, who has been studying maternal behavior for 25 years.

“These new neurons may have a role in recognizing pups or associating their smell with the mother’s behavior, so that during lactation or when [the rats] reproduce later and smell pups, they respond faster. But we don’t know—that’s a hypothesis,” he says.

In continuing his research, Bridges will more closely examine whether the new neurons play a role in how the adoptive moms as well as mothers that give birth remember to be maternal when exposed to young later in life. He wants to determine if the adoptive moms, like the biological moms, undergo “a reprogramming of the brain so they respond to pups more readily later on.”

Catherine O’Neill Grace, the editor of Tufts Veterinary Medicine magazine, can be reached at catherine.grace@tufts.edu.

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