Helping behavior is associated with increased affiliative behavior, activation of the prosocial brain network and elevated oxytocin receptor expression in the nucleus accumbens

A prosocial response to others in distress is increasingly recognized as a natural behavior for many social species, from humans to rodents. While prosocial behavior is more frequently observed towards familiar conspecifics, even within the same social context some individuals are more prone to help than others. For instance, in a rat helping behavior test, rats can release a distressed conspecific trapped inside a restrainer by opening the restrainer door. Typically, rats are motivated to release a trapped cagemate, and consistently release the trapped rat ( openers), yet around 30% do not open the restrainer ( non-openers). To characterize the difference between these populations, behavioral and neural activity were compared between opener and non-opener rats tested with a trapped cagemate in the helping test. Behaviorally, openers showed significantly more social affiliative behavior both before and after door-opening compared to non-openers. Analysis of brain-wide neural activity based on the immediate early gene c-Fos revealed increased activity in openers in the previously identified prosocial neural network compared to non-openers. The network includes regions associated with empathy in humans (somatosensory cortex, insula, cingulate cortex and frontal cortex), and motivation and reward regions such as the nucleus accumbens. Oxytocin receptor mRNA expression levels were higher in the accumbens but not the anterior insula. Several transcription control pathways were also significantly upregulated in openers accumbens. These findings indicate that prosocial behavior may be predicted by affiliative behavior and activity in the prosocial neural network and provide targets for the investigation of causal mechanisms underlying prosocial behavior. Significance StatementProsocial behavior is observed in many social species, including rodents, yet the determinants underlying why some animals help and others do not is poorly understood. Here, we show behavioral and neural differences between prosocial and non-prosocial pairs in a rat helping behavior test, with increased social interaction and nucleus accumbens oxytocin receptor gene expression in animals that helped.