Bromances may be good for men's health

http://www.eurekalert.org/pub_releases/2016-03/uoc--bmb030316.php

Public Release: 3-Mar-2016
Bromances may be good for men's health
Moderate stress encourages male bonding, and prosocial behavior makes them more resilient to stress
University of California - Berkeley

Male friendships, portrayed and often winked at in bromance movies, could have healthful effects similar to those seen in romantic relationships, especially when dealing with stress, according to a new study of male rats by researchers at the University of California, Berkeley.

Human studies show that social interactions increase the level of the hormone oxytocin in the brain, and that oxytocin helps people bond and socialize more, increasing their resilience in the face of stress and leading to longer, healthier lives. Studies of male-female rat pairs and other rodents, such as monogamous prairie voles, confirm these findings.

The new study extends these studies to male rats housed in the same cage, and demonstrates that mild stress can actually make male rats more social and cooperative than they are in an unstressed environment, much as humans come together after non-life-threatening events such as a national tragedy. After a mild stress, the rats showed increased brain levels of oxytocin and its receptor and huddled and touched more.

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"Having friends is not un-masculine," she added. "These rats are using their rat friendships to recover from what would otherwise be a negative experience. If rats can do it, men can do it too. And they definitely are, they just don't get as much credit in the research for that."

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The research also has implications for post-traumatic stress disorder, said senior author Daniela Kaufer, a UC Berkeley associate professor of integrative biology and member of the Helen Wills Neuroscience Institute.

After severe, potentially life-threatening stress, the male rat cagemates became withdrawn and antisocial, often sitting alone in a corner, and more aggressive, not unlike people who suffer from PTSD or illnesses such as depression or severe anxiety. The researchers found that oxytocin receptor levels in the brain actually decreased after severe stress, which would make the brain less responsive to whatever hormone is there.

"Social interactions can buffer you against stress, but if a trauma is just too much and there is PTSD, you actually withdraw from social interactions that can be supportive for you," Kaufer said. "This research suggests that this might be happening through changes in oxytocin; that in the context of life-threatening stress, you lose its effect and you see less prosocial behavior. This really aligns well with what you see with pathological effects of stress on humans."

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Male rats housed together, Kirby said, sometimes display aggression toward one another, such as fighting over water and food. But after a mild stress - in this experiment, restraining them for a few hours - they tended to cooperate more, despite or because of an even stronger dominance hierarchy between the rats.

"If you repeatedly take away and return their water, normal rats become very aggressive, pushing and shoving at the water fountain like a bunch of thirsty 7-year-olds who don't know how to stand in line yet," Kirby said. "The cagemates who had the mild stressor did not show this behavior at all. After taking away their water and bringing it back, they shared it very evenly and without any pushing and shoving. It was very civil."

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The researchers found that this was accompanied by increased hypothalamic oxytocin levels.

On the other hand, a severe stressor - in this case, adding the smell of fox urine while they were restrained - had the opposite effect.

"If you are a rat and you smell a predator, the likelihood that you are going to get eaten soon is pretty high," Kirby said. "In that case, the oxytocin bump that would come with a less threatening stressor is suppressed, and oxytocin receptor levels decrease Then, you don't see social bonding anymore. You don't see the rodent cuddling, you don't see them showing increased prosocial behaviors."

This is akin to PTSD after a battle experience or a car accident, she said. "People stop talking to their friends, they stop engaging in their social networks the way they used to."

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