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The Great Rat Mother Switcheroo

Thursday, January 10, 2013 - 03:10 PM

One of the most-asked questions after our Inheritance show had to do with our rat-licking segment.

In this ten-minute story -- part of our larger conversation on Lamarck -- researchers Michael Meaney and Frances Champagne spoke about maternal behavior in rats, and its effects on offspring.

As we reported, the duo's lab work shows that when a mother rat licks a pup (her sign of "I love you"*), the action sets off a Rube Golberg-esque cascade of hormones, which ultimately wind up all the way down at the level of the DNA.

What do those hormones do down there? It turns out, they change the chemical markers, or epigenome, surrounding certain areas of the DNA. And the end result of these changes hinges on how much the rat pup is licked: if a rat pup gets a lot of licks, the epigenetic changes cause the pup to grow up and lick its own kids a lot; if a pup doesn't get a lot of licks, the chemical changes cause that pup to be a low-licker. In both cases, the pattern of maternal behavior is carried across generations -- from grandmothers to mothers to grandkids. Or, in the words of Radiolab producer Soren Wheeler, "It's as if the epigenetic information leaps up out of the mother's genes through a tongue and lands back on the babies' genes." (Interested? Go listen to the show for more!)

BUT, but… many of our savviest listeners posed a follow-up question: how were the researchers sure that an epigenetic change triggered the offspring's maternal behavior, and not just a simple gene, passed on through the mother's lineage? Touché, my friends. It's a great question, and one we can answer -- the researchers tested your theory.

With different litters of rats, the researchers did some baby/mother rearranging (called "cross-fostering" studies). The experiment wasn't too complicated: within 12 hours of the pups being born, they took pups born of high-licking mothers and placed them with low-licking foster mothers, and vice versa (they took pups born of low-licking mothers and placed them with high-licking foster moms). And they controlled the experiment by making sure not to switch too many rat babies amongst the mothers -- they didn't want to scare the mothers or the babies into acting differently. So, once the rats were rearranged, they hung out in their new homes for one week, the normal time for a rat baby to stay in a nest. And though this whole paragraph reads like a bit of a tongue-twister, the end result was quite straightforward: the rats took on the characteristics expressed by their foster mother, not their biological mother.

The switching method also revealed proof of another connection. It turns out there's also an epigenetic link between maternal behavior and stress. The rats that were reared by high-licking mothers grew up to be less stressed as adults than those raised by low-licking mothers. They saw this was true for female pups as well as male pups; it wasn't just passed down the maternal line. And they saw that if they took babies from a low-stress mother and put them in a high-stress foster situation, the pup took on the characteristics of the mother rearing it. (The reverse was also true: pups born to high-stress moms but raised by low-stress ones turned out less stressed). According to the researchers' 1999 paper on the topic, "These findings suggest that individual differences in the expression of genes in brain regions that regulate stress activity can be transmitted from one generation to the next through behavior." Because that behavior causes an epigenetic change.

And while this all might sound a bit dreary -- your outlook on life and your own parenting is determined by how you are raised...something you don't have control over -- one bit of research made it seem quite uplifting to me: if the high-stress rats were put in a low-stress environment as adults (remember: in every other situation we're talking about rats that are one week old or less), epigenetic markers were still changed... resulting in a low-stress animal. Things aren't set in stone like they seem! And it pays to get a stress ball. Or, maybe, a rat.**

* Rats love on each other with licking, nuzzling, and grooming, as well as mothers laying on top of their pups in a sort of smother hug. The pup's fur is actually covered in salt, which a mother rat finds delicious. But for those of you who watched the video, you may wonder, what's with all that butt-licking? Turns out, a mother's licking not only results in some epigenetic tinkering, it's also critical to the rat pups health: a baby that is not licked would die (hence the scientists always talk about low-licking, not no-licking). Why? The licking activates specific body functions, that are key to life. That's right, you guessed it: Mama Rats must lick the babies' butts so they can poop.

** And for those of you that are inwardly grimacing at all this talk of rat love, Michael told me in a phone interview that despite how they are viewed, rats are actually VERY social creatures, and the ideal first pet for any family. What's that? Is that a new rat meme I'm sensing? LOLRats... I'll leave that to you.

*** Thanks to Frances Champagne for sharing some of her research footage of rat moms and pups, which we used with permission for the above image and GIF.


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Comments [7]

joanne rossettie from 17901

I have a male rat I bought from a pet store ( caged with a rescue rat) who licks my nose every morning! He is the most affectionate of the four! He must have been raised by a loving rat mom? Also the rescue rat Tony was near death when I got him. Wondering if his subsequent healing and good health now might be attributed to his loving companion, Mickey?!

Nov. 25 2014 06:48 AM
Kasler D from Li, NY

It makes perfect sense that the rats that were shown more love grew up to he less stress then the other rats that were raised by low-licking rats . This controlled experiment shows that where you come from has a great affect on you later as seen with the rats.

Sep. 26 2013 11:27 PM
duno from sometimes

nce report Молy
lol, Soren, do you have ur backgr on IT

Jan. 16 2013 04:24 AM
Sam S.

Hi Max,

To answer your question in brief, yes, the behavioral profiles of these animals are modifiable by environmental experiences, however, it really depends on the environmental context these animals are in. In certain situations, they remain fearful, while in others, their learned experiences can override any programmed behaviors they may be biased toward. What is interesting about this is that the genes that have been epigenetically modified don't change. This means that other areas of their brain are changing to alter their behavior when exposed to new environments.

I hope that helps clarify things. For a more in depth answer, please see this paper:

Jan. 15 2013 11:35 PM
Sam S. from Berkeley

Hi Andres,

To answer your question, yes, researchers were able to pin down specific modifications by running a battery of tests on those rats brain tissue. Epigenetic modifications leave residues on the DNA itself, this change in structure can be tested for. In this case, specific modifications to those genes which are involved in the stress axis were found. This work was done by a researcher named Ian Weaver.

I hope that answers your question.

Jan. 15 2013 11:22 PM

Just wondering, why do they think their epigenome got altered? Did they pin out the precise modification?. Couldn't this be a simple case of learned behavior?.

Jan. 14 2013 07:08 AM
Max Hittesdorf from Colorado

I am just wondering what can be implied from the statement: "Things aren't set in stone like they seem!". Other than befriending a rat and a stress ball in order to be happy, the conclusion that you come to, Ms. Webster, seems to suggest that the epigenome in rats (and perhaps larger, more complex mammals) is in fact flexible/dynamic, or rather that it can change, either in an evolutionarily positive or negative way, based on changes in the environment. This flexibility allows for some tangible physical benefits as seen in the rat study where high-stress rats placed in low-stress environments still show epigenetic markers. However, this doesn't quite negate the fact that the rats were licked less by their mothers as pups and are therefore naturally inclined to be more stressed. Thus, do these high-stress rats just return back to their natural state when they are taken out of the low-stress environment? Is there a point at which the high-stress rats become one of the low-stress rats because they've spent so much time in the new environment? Perhaps it could happen the other way around too - i.e. low-stress rats become stressed in a high-stressed environment.

Jan. 14 2013 01:58 AM

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