A wagging tail, a loving lick, a playful leap, a heart-melting look. Do you know when your puppy is happy to see you.
Now, new research by Japanese scientists suggests that the animal’s eyes can fill with tears of happiness when they are reunited with their owner after a period of absence.
Tears can help cement the bond between humans and dogs – a relationship that goes back tens of thousands of years.
Like humans, dogs have tear ducts that fill with tears to keep their eyes clean and healthy. But tears in dogs, which tend not to fall like when humans cry, hadn’t been associated with emotion before.
Takefumi Kikusui, a professor at the Laboratory of Human-Animal Interaction and Reciprocity at the University of Azabu in Japan, decided to investigate the matter after observing a pattern in one of her two poodles when she had puppies six years ago. He noticed her eyes watering as she nursed her babies.
“We found that dogs shed tears associated with positive emotions,” said Kikusui, co-author of the research published in the journal Current Biology, in a press release.
“We also made the discovery of oxytocin as a possible underlying mechanism,” continued Kikusui, referring to the hormone that in humans is popularly called the love or maternal hormone.
To investigate the link, Kikusui and his team measured the amount of tears among 18 dogs with a standard test known as the Schirmer Tear Test. It involves a strip of paper placed inside the dogs’ eyelids for one minute before and after they are reunited with their owners after periods of five to seven hours of separation.
“The tear volume was evaluated by the length of the wet part in the STT. The baseline was around 22mm and the owner meeting increased by 10%,” explained Kikusui via email.
With the help of 20 dogs, the researchers compared the amount of tears before and after meetings 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 the production of tears, a solution containing the hormone was applied to the surface of 22 dogs’ eyes. The amount of tears significantly increased after application of oxytocin compared to a control solution.
There’s still a lot researchers don’t know about dog tears. Humans often cry in response to negative emotions, but the researchers did not test to see if dogs did the same. They also don’t know if a dog’s ability to tear plays a social role in the canine world.
Kikusui points out that it’s possible that humans take better care of dogs with tears in their eyes. His team showed 74 people pictures of dogs’ faces with and without artificial tears and asked them to rate the animals. People gave more positive responses when they saw dogs with tears in their eyes.
“Dogs have become partners with humans,” Kikusui said in a statement, “and we can form bonds with them.”
Source: CNN Brasil
