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Tag: mice
Stress Reaction May Be In Your Dad’s DNA, Study Finds

Stress Reaction May Be In Your Dad’s DNA, Study Finds

By Geoffrey Mohan, Los Angeles Times (TNS)

Stress in this generation could mean resilience in the next, a new study suggests.
Male mice subjected to unpredictable stressors produced offspring that showed more flexible coping strategies when under stress, according to a study published online Tuesday in the journal Nature Communications.

The secret might be hidden in a small change in how certain genes are regulated in the sperm of the father and in the brains of offspring, the study found.

Several studies have shown that stress in early life not only can affect the individual’s behavior and cognitive functions, but can affect the next generation. So researchers have been eager to find any trace of changes in DNA coding that might underlie their observations.

Before you pen a “thanks for the resilience” Father’s Day card, consider: The study involved mice, not humans. More important, even the seemingly more resilient mice had lots of negative behaviors — depression and anti-social tendencies among them.

“If we look at the whole behavior of these animals, the benefit is really a very small proportion of the effects,” said study co-author Isabelle Mansuy, a neuroscientist at the University of Zurich’s Brain Research Institute. “Most other effects are fairly negative, because the animals are depressed, are anti-social, and have cognitive impairment.”

Researchers tried to mimic the effects of erratic parenting and a stressful home environment. So they separated male mouse pups from their mothers for several hours a day over the first two weeks of life, during which time they were occasionally restrained or forced to swim for five minutes — all at unpredictable intervals.

The mice then matured in social groups of four or five unrelated mice of the same sex that had equally unpredictable childhoods. Then they were matched to females, producing pups of their own. Once the pups grew up, they were subjected to various mazes that test the ability to show goal-oriented and flexible behavior under stress.

Compared with a control group, the offspring of stressed dads showed less hesitation in exploring an arm of a maze. And when offered the choice of getting a drink of water immediately or waiting for sugared water, the offspring of stressed males tended to wait for the greater reward. They also were better at figuring out changed rules — rewards that were moved from one spot to another, or cues that were changed.

Numerous studies of the effects of stress implicate a loop in the brain’s limbic system, which mediates emotion and causes the release of the stress hormone cortisol. That chemical can amp up a feedback loop to the brain.

Much of this stress-related reaction in the brain is mediated, in part, by a mineralocorticoid receptor, or MR, in brain cells.

The study found small changes in regulatory DNA sequences near an MR gene in sperm cells of the stressed mice. Such changes in gene regulation in response to the environment are known as epigenetic processes. The study found epigenetic markers associated with a half-dozen genes in the brain cells in the hippocampus of the offspring of stressed male mice.

Together, these changes offer a hint at a possible path for passing the effects of stress from one generation to the next.

Soldiers may offer a prime example, Mansuy said. “Many soldiers are people from lower socioeconomic environments and many of them have been exposed to violence, to broken families and to bad conditions when they were young,” she said. “And many of these people are stress-resilient, and they also have some adaptive advantages when they are placed in a situation of danger or challenge. They have developed coping strategies perhaps that other people have not.”

Still, she noted, these enhanced resiliency behaviors were “the only benefit” observed among the mice.

Researchers have been trying to untangle the effects of genetics and family background in post-traumatic stress disorder among soldiers returning from war.

Photo via WikiCommons

Lab Mice Get Addicted To Sun Exposure

Lab Mice Get Addicted To Sun Exposure

By Deborah Netburn, Los Angeles Times

LOS ANGELES — Does basking in the sun make you feel relaxed and happy, like nothing can bother you? There may be a biological reason for that.

Researchers found that mice who were regularly exposed to UV light had a higher pain tolerance than mice that were not exposed to UV light. They also experienced withdrawal symptoms when the UV light was taken away.

In other words, the mice’s response to the UV radiation was similar to what would happen if the scientists had given them low doses of heroin.

“I know people are thinking, heroin and UV radiation, give me a break,” said David Fisher, professor of dermatology at Harvard Medical School and Massachusetts General Hospital, who led the study. “But we think there could be evolutionary reasons for it.”

Previous studies had already established that people who obsessively frequent tanning salons can exhibit addictive behaviors, but nobody knew exactly what was triggering that response.

“What our study added is the mechanism,” Fisher said. “How does it happen.”

Fisher and his team started their series of experiments by shaving the backs of mice and exposing them to UV radiation five days a week for six weeks. Each exposure was designed to be similar to what fair-skinned people in Florida would experience if they spent 20 to 30 minutes in mid-day summer sun.

Within the first week, the researchers found that the UV-exposed mice had elevated levels of beta-endorphins — a naturally occurring opioid — circulating throughout their bodies.

This wasn’t a huge surprise for the scientists. They already knew that beta-endorphins were produced in the skin in response to UV radiation. What they didn’t know was whether it was possible for beta-endorphins produced in the skin to affect the mice’s behavior.

To find out, they put the mice through a series of tests. They discovered that mice that had been exposed to UV radiation were less sensitive to heat and pain than their non-UV exposed counterparts. When they treated the UV-exposed mice with naloxone, a drug that inhibits opioids in the body, the same mice responded totally normally to these tests of pain.

The researchers also found that the UV-exposed mice became addicted to the elevated levels of beta-endorphins. Mice that received naloxone after days of UV exposure showed classic signs of opioid withdrawal like paw tremor, teeth chatter, and wet dog shake.

Fisher said there are two reasons it made sense to do this study on mice. “It happens that the response of skin to UV radiation is remarkably similar in mice and humans,” he said. “Mice tan, and the same gene regulates pigment in mice and in people.”

He added that using a mouse model also allowed the team to ask very specific questions about the mechanisms that make sun exposure addictive. For example, they ran the same tests described above on mice that were missing the beta-endorphin gene. These mice did not exhibit any change in their pain threshold when they were exposed to UV light, nor did they show any withdrawal symptoms when given naloxone.

“That is enormous,” Fisher said. “Now we know that UV light and increased beta-endorphins don’t just correlate, but that the endorphin is mediating behavior.”

The researchers hypothesize that this feel-good feeling we get from the sun may have once been physically beneficial for humans who were perhaps not getting enough vitamin D.

Fisher said he hopes that the study, published in the journal Cell, will help people better understand why sunbathing continues to be so seductive, in spite of all the ways we now know it harms our skin.

“There is real damage that comes from frequent UV exposure,” said Fisher. “If people recognize that their behavior of going out and tanning may go beyond a conscious decision, maybe they will be better able to avoid it.”