Stress primes ‘teen’ rats for tough times later

"Unpredictable stress can have dramatic and lasting consequences, both for humans and for free-living animals," says Lauren Chaby. "Unpredictability is part of what can make stress so toxic" (Credit: Matt Baume/Flickr)

Rats that experience frequent physical, social, and predatory stress during adolescence solve problems and forage more efficiently as adults—even when under high-threat conditions.

The findings may provide insights into how teenagers respond to stress, a new study suggests.

“Even though the stressed rats were really run through the gamut, they do not come out with an overall cognitive deficit,” says Lauren Chaby, PhD student in neuroscience and ecology at Penn State. “What they do have is this context-specific performance that’s linked to the environment that they experienced during adolescence.”

Researchers were interested in the effects of maltreatment and adverse environments during human adolescence and used rats because their short lifespan makes it possible to study long-term effects more efficiently.

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Adolescent rats were exposed to a range of unpredictable stressors, including smaller or tilted cages, social isolation or crowding, and predator scents or vocalizations.

“Unpredictable stress can have dramatic and lasting consequences, both for humans and for free-living animals,” Chaby says. “Unpredictability is part of what can make stress so toxic.

“You don’t have control over your environment, you don’t have control over what’s going to happen next, you’re not able to predict it. So we tried to use a range of stressors so the rats couldn’t predict which stressor was going to come next.”

The researchers then tested adult animals to see if there were lasting effects of stress in adolescence. Many previous studies investigating the consequences of stress during early life or adolescence test adult animals under standard conditions that usually reflect a safe environment—little noise or external threats, and dim lighting that is preferred by nocturnal rats.

‘Live-fast die-young’

“So you have this relaxed situation that they’re trying to solve these tasks in,” Chaby says. “But this isn’t really fair, since some of the animals are used to this and some of the animals aren’t. So we wanted to test them in conditions that were consistent with their rearing conditions to see if that impacted their ability to solve tasks.”

For the study, published in the journal Animal Behaviour, researchers tested the ability of 24 adult rats to solve problems while foraging for food under both standard and high-threat conditions—bright light, a taxidermy hawk swooping overhead, and hawk vocalizations. Adult rats then manipulated a variety of novel objects to obtain food rewards.

Under high-threat conditions, adult rats stressed during adolescence started foraging sooner, visited 20 percent more food patches, and obtained 43 percent more food than a control group of unstressed adult rats. The findings suggest that growing up in a stressful environment can prepare rats for a stressful, high-predation environment in the future.

Surprisingly, previously stressed rats did not show any costs of this enhanced performance. Under standard conditions, stressed rats took significantly longer—17 percent—to visit the first food patch due to initial wariness, but ultimately ate the same amount of food as unstressed rats who began foraging more quickly.

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“And that’s one of my favorite findings, because I always think that’s so cool when you have animals that are doing things in two different ways but are coming to the same performance outcome,” Chaby says.

There may still be a cost of this enhanced performance that occurs over a longer period of time. For example, they could have a “live-fast die-young strategy,” says Chaby, who says she hopes the findings can help direct how we study adolescent stress in humans.

“I think that addressing this empirically in a model where we have internal control can really allow us to at least understand what questions we should be asking about ourselves.”

The Pennsylvania Department of Health using Tobacco CURE Funds partially funded the work.

Source: Penn State