Increase of tear volume in dogs after reunion with owners is mediated by oxytocin.

In humans, tear volume increases during emotional arousal. To our knowledge, no previous studies have investigated the relationship between emotional arousal and tear volume in animals. We performed the Schirmer tear test (STT) and measured tear volume in dogs before and after reunions with owners and familiar non-owners. Tear volume increased significantly during reunion with the owner, but not with a familiar non-owner. When an oxytocin solution was applied to dogs' eyes, the tear volume also increased, suggesting that oxytocin might mediate tear secretion during owner-dog reunions. Finally, human participants rated their impressions on photos of dogs with or without artificial tears and they assigned more positive scores to the photos with artificial tears. These results suggest that emotion-elicited tears can facilitate human-dog emotional connections. VIDEO ABSTRACT.