Prosocial behavior, which is defined as the voluntary behavior intended to be benefit for another, is often observed in animal, as well as human. Previously, several studies have shown that physical exercise may facilitate prosocial behavior, but the neural mechanisms underlying the facilitatory effect of exercise on prosocial action remains unclear. It has been suggested that empathy is one of the most essential factors for the prosocial behavior, and may be involved in oxytocin (OXT) neurons. Thus, it is possible that exercise may affect the prosocial behavior via activity of OXT neurons. However, few experimental studies for prosocial behavior have focused on the effect of exercise, and on its neural mechanisms. In the present study, we examined the effects of long-term voluntary exercise (4 weeks) on helping behavior for soaked conspecifics in male rats, and on neuronal activity of OXT neurons in the hypothalamic paraventricular nucleus (PVN) during helping situation using immunohistochemistry. We also measured neuronal activities in the central nucleus of the amygdala (CeA) and corticotropin-releasing factor (CRF) neurons in the PVN in both helping (observer) and soaked (demonstrator) rats, because these activities are suggested to related to empathetic concern in the prosocial behavior. Helping rats were assigned one of two groups to alter the exercise condition; housing in the cage with or without running wheel (EX or no-EX). All the helping rats were individually housed in each cage for 4 weeks, because the individual familiarity may affect ability of empathy even to prosocial behavior. Then, we observed a helping behavior that a helping rat opens the door to help a soaked rat in pool area containing water. The time to door-opened was recorded for 6 consecutive days (maximum for 5 min/day). In addition, the time spent in interaction zone that is near to door and the duration of grooming were also observed. There is no significant difference in the time to door-opened between EX and no-EX groups. Interestingly, the time spent in interaction zone and the duration of grooming in the EX group were longer than those in the no-EX group. These results suggest that long-term voluntary exercise with individually housing may not facilitate prosocial behavior, but may enhance an ability of empathy. The results of neuronal activity are under consideration.

研究助成：Research funds : KAKENHI JP18K10852