If you slam your hand in the car door and experience physical pain, medical science can offer you a “pain killer!“. Certainly morphine (via its activation of the mu opioid receptor (OPRM1)) will make you feel a whole lot better. However, if your boyfriend or girlfriend breaks up with you and you experience emotional pain, its not so clear whether medical science has, or should offer, such a treatment. Most parents and doctors would not offer a pain killer. Rather, it’s off to sulk in private, perhaps finding relief in the writings of countless poets who’ve attested to the acute pain that ensues when emotional bonds are broken.
Love hurts! But why should this be? Why does the loss of love hurt so much?
From a purely biological point of view, it seems obvious that during certain periods of life – childhood for instance – social bonds are important for survival. Perhaps anything that helped make the breaking of such bonds feel bad, might be selected for? Its a very complex evolutionary genetic problem to be sure. One way to begin to solve this question might be to study genes like OPRM1 and ask how and why they might be important for survival.
Such is the case for Christina Barr and colleagues, who, in their paper, “Variation at the mu-opioid receptor gene (OPRM1) influences attachment behavior in infant primates” [doi:10.1073/pnas.0710225105] examine relationships between emotional bonds and genetics in rhesus macaques. The team examines an amino acid substitution polymorphism in the N-terminus of the OPRM1 protein (C77G which leads to an Arginine to Proline change at position 26). This polymorphism is similar to the human polymorphism (covered here) A118G (which leads to an Asparagine to Aspartate change at position 40). Binding studies showed that both the 77G and 118G alleles have a higher affinity for beta-endorphin peptides.
Interestingly, Barr and colleagues find that the classical “pain gene” OPRM1 G-allele carrier macaques display higher levels of attachment to their mothers during a critical developmental phase (18-24 months of age). These G-allele carriers were also more prone to distress vocalizations when temporarily separated from their mothers and they also spent more time (than did CC controls) with their mothers when reunited. Hence, there ?may be? some preliminary credence to the notion that a gene involved in feeling pleasant/unpleasant might have been used during evolution to reinforce social interactions between mother and child. The authors place their results into a larger context of the work of John Bowlby who is known for developing a theory of attachment and the consequences of attachment style on later phases of emotional life.