Social approach to pain in laboratory mice

Abstract

It has been recently demonstrated that pain behavior in the mouse can be modulated by the presence of a conspecific, but what remains unclear is whether such pain behavior can serve the function of soliciting social approach. Using a novel social approach paradigm, we tested mice in various dyadic or triadic conditions, including “jailed” mice—some in pain via intraperitoneal injection of 0.9% acetic acid—and test mice free to approach or avoid the jailed mice. We observed a sex-specific effect whereby female, but not male, test mice approached a familiar same-sex conspecific in pain more frequently than an unaffected familiar or unfamiliar, but affected, conspecific. Despite a substantial literature emphasizing oxytocin's role in affiliative and pair-bonding behavior, this effect was also observed in female mice lacking the oxytocin receptor, suggesting that pain-related social approach may not be mediated by oxytocin. Furthermore, we found that the frequency of contact by the test mouse was negatively correlated with the pain behavior of the jailed mouse, suggesting that proximity of a familiar unaffected conspecific may have analgesic properties.

Keywords:

• Pain inhibition
• Sex differences
• Social communication

Acknowledgements

This research was supported by a National Science Foundation research in undergraduate institutions (RUI) grant and a Haverford College Faculty Research Grant to WFS, and a grant from the Louise and Alan Edwards Foundation to JSM. DJL was supported by a CIHR CGS Doctoral Award, and AHT was supported by a research fellowship from the Arnold and Mabel Beckman Foundation. We are grateful to Dr Larry Young for providing oxytocin receptor knockout mice. DJL and AHT contributed equally to this paper.