Social Familiarity-Dependent Modulation of Emotional Responses to Stressed Conspecifics and the Role of Oxytocin Receptors in Rats.

Empathy, the ability to recognize and respond to others' emotions, enables individuals to experience emotions that either align with or differ from those of others. In rodents, emotional contagion is well established, as they reflexively express similar negative emotions when exposed to a stressed conspecific. However, because emotional responses toward others do not always result in direct contagion, whether they can modulate their emotional responses based on the social context remains unclear. Therefore, this study aimed to investigate whether rats exhibit distinct emotional responses to stressed conspecifics restrained in a container, depending on familiarity as a social factor. The elevated plus maze was employed as a method capable of capturing a broad range of emotional responses. Our findings revealed that, compared with a control condition without a conspecific, observer rats exhibited different emotional responses depending on the familiarity of the stressed conspecific. When paired with a familiar stressed conspecific, they showed increased anxiety-like behavior, spending less time in the open arms of the maze. By contrast, when paired with an unfamiliar stressed conspecific, they spent more time in the open arms displaying greater exploratory motivation. These context-dependent emotional responses were suppressed by intracerebroventricular administration of an oxytocin receptor antagonist (L-368,899 hydrochloride), targeting a neuropeptide that regulates sociality. The present findings suggest that rats not only mirror the emotions of stressed conspecifics, but also are capable of adjusting their emotional responses based on the social context, which may reflect their ability to consider both the emotions and social situations of others adaptively.