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"Love hormone" may mediate wider range of relationships than previously thought

palsOxytocin, a veritable pipsqueak of a protein (or "peptide" in science-speak) punches well beyond its weight. If you're a woman, oxytocin induces uterine contractions leading to childbirth and, afterward, induces lactation. It's also often called the "love hormone," because it's secreted in a woman's brain during sexual arousal and appears to be involved in both men's and women's experience of falling in love, as well as in parent-child bonding.

In a just-out Nature study, Stanford neuroscientist Rob Malenka, MD, PhD, and his colleagues have shown just how oxytocin may figure into a much broader range of social interactions - and, possibly, in neurological disorders such as autism.

In fact, oxytocin has been administered to autistic children in clinical trials. The new study pinpoints a unique way in which oxytocin alters activity in a part of the brain that is crucial to experiencing the pleasant sensation neuroscientists call "reward," as is explained in a news release about the study:

"People with autism-spectrum disorders may not experience the normal reward the rest of us all get from being with our friends," said [Malenka]. "For them, social interactions can be downright painful. So we asked, what in the brain makes you enjoy hanging out with your buddies?"

The researchers actually "asked" mice, not people, this question. They let each of their experimental subjects spend 24 hours in a room filled with "buddies" (a mouse's littermates) and another 24 hours in a room devoid of pals. Then they gave each mouse his choice of rooms (all the mice were males) and measured how much time he spent in each of them. Sure enough, the guests overwhelmingly favored the room whose look, feel, and smell brought back happy memories of time spent socializing.

But when the researchers played a trick on the mice's brains that disrupted the action of oxytocin in the nucleus accumbens, an area of the brain intimately involved in the sensation of reward, the mice lost their preference for the boom-boom room. If something's no fun anymore, it stands to reason that you're going to want to do a lot less of it.

The scientists then embarked on a series of sophisticated experiments that showed precisely what brain connections are involved in the link between oxytocin and the sensation of reward.

Earlier studies have found significantly lower levels of oxytocin in blood plasma of autistic children, but until now nobody knew anything about what, exactly, the connection between oxytocin, reward, group activity and autism might be.  The new findings go a long way toward explaining that connection.

Previously: Revealed: The brain's molecular mechanism for why we get the blues, Better than the real thing: How drugs hot wire our brains' reward circuitry and Stanford study reveals why human voices are less rewarding for kids with autism
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