Aug 13, 2009 - Research

Genetic Variation In Morphine Receptor May Play A Part In Coping With Social Rejection

Two young girls bullying other young girl outdoors

It’s no accident that we often refer to rejection or insult as a slap in the face – research shows the same brain signaling pathways are involved in both physical and emotional pain.

And morphine, a drug well known for its ability to dull physical pain, also reduces separation-induced emotional distress in monkeys, dogs, guinea pigs, rats and chickens.   This is thought to depend on changes in signaling through a morphine receptor called MOR (mu-opioid receptor) that is also implicated in emotional pain in humans. Studies have shown that signaling through MOR is reduced when women recall upsetting events like the death of a loved one or the breakup of a romantic relationship.

Given that MOR seems to be at the center of the overlap between physical and emotional pain, researchers from the UCLA Department of Psychology wondered whether a genetic variation in the gene that encodes MOR that is already known to impact sensitivity to physical pain might also affect how thick-skinned a person is.

Baldwin M. Way and colleagues surveyed 122 healthy young adults about their sensitivity to social rejection.   The assessment measured the tendency of study subjects to be fearful that social interactions will result in hurt feelings, criticism and being a burden to others.   The results, published online this week in the Proceedings of the National Academy of Sciences, show that people with one or two of the variants had significantly higher levels of self-reported sensitivity to social rejection. The variants are also associated with needing more morphine for pain relief after surgery.

A subset of the study participants also had their brains scanned in an fMRI machine while playing an online ball-tossing game.   The subjects thought they were playing with two people, but in reality they were interacting with a pre-set computer program.   The game simulated social rejection by having the subjects’ virtual playmates leave them out of the fun.

Just as in the survey, the variant was associated with heightened responses to social rejection.   Higher brain activity was recorded in the anterior cingulate cortex and the anterior insula brain regions associated with the processing of both physical and emotional pain, in people with one or two of the variants.

As is usually the case, the results of this study should be considered preliminary until other researchers replicate them. But based on their results, along with previous research, the authors conclude that, “… at multiple biological levels, including the neurochemical, neuroanatomical, and now genetic, feeling hurt physically shares more than just linguistic commonality with feeling hurt socially.”

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