Dogs' eyes well up with tears of joy when reunited with their owners
New research has suggested a dog's eyes well up with tears of happiness when reunited with their owner after a period of absence. The tears may help cement the bond between human and dog -- a relationship that goes back tens of thousands of years.
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Now, new research from Japanese scientists suggests that a dog's eyes may well up with tears of happiness when reunited with their owner after a period of absence. The tears may help cement the bond between human and dog -- a relationship that goes back tens of thousands of years.
Like humans, dogs have tear ducts that well up with tears to keep their eyes clean and healthy. But tears in dogs, which tend not to fall as they do when humans cry, hadn't been linked with emotion before.
Takefumi Kikusui, a professor at the Laboratory of Human-Animal Interaction and Reciprocity at Azabu University in Japan, decided to investigate dog tears after watching one of his two standard poodles when she had puppies six years ago. He noticed that her eyes got teary as she nursed her puppies.
"We found that dogs shed tears associated with positive emotions," Kikusui, who coauthored the research that published Monday in the journal Current Biology, said in a news release.
"We also made the discovery of oxytocin as a possible mechanism underlying it," Kikusui said, referring to the hormone that in humans is sometimes called the love or maternal hormone.
With the help of 20 dogs, researchers then compared the amount of tears before and after reunions with their owners and people with whom the animals were familiar. Only the reunion with the owner increased the amount of tears.
To understand whether oxytocin played a role in producing the tears, a solution containing the hormone was applied to the surface of 22 dog' eyes. The amount of tears significantly increased after the oxytocin was applied, compared with a control solution.