CD38-mediated oxytocin signaling in paraventricular nucleus contributes to empathic pain

Empathy plays a crucial role in social communication and the perception of affective states and behavioral processes. In this study, we observed that empathic interaction with a mouse experiencing pain resulted in decreased mechanical pain thresholds and anxiety-like behaviors in its bystander, though the underlying mechanisms remain unknown. We demonstrated that CD38 expression in the paraventricular nucleus (PVN) was upregulated during empathic pain, and the pain and emotions of CD38 knockout (CD38KO) mice as bystanders were not affected. Furthermore, fiber photometry recordings indicated that calcium activities of PVN neurons were increased during empathic pain. Interestingly, direct chemogenetic inhibition of PVN neurons attenuated the hyperalgesia and anxiety-like behaviors associated with empathic pain. In contrast, activating PVN neurons through chemogenetics in CD38KO mice induced hyperalgesia and anxiety-like effects in empathic pain. Oxytocin levels in PVN were upregulated during empathic pain, while CD38KO mice inhibit the upregulation in OXT levels, confirming that CD38 is involved in releasing brain OXT and that the CD38-OXT system in the PVN plays a role in empathic pain. Collectively, CD38-mediated oxytocin signaling in PVN is closely linked to empathic pain through its effect on the activation of PVN neurons, and it could be viable targets for novel empathic behavior interventions.