Sagamihara, Japan - Dogs can shed tears of joy when reunited with their human masters, Japanese researchers at Azabu University have found, according to the results of a study published in the journal Current Biology.

A team led by researcher Takefumi Kikusui investigated whether our four-legged friends sometimes cry when they get too excited.

"We found that dogs shed tears associated with positive emotions," Kikusui explained. "We also made the discovery of oxytocin as a possible mechanism underlying it."

Kikusui and his colleagues made the discovery after one of his two poodles had puppies. While nursing her puppies, something changed on her dog's face: she had actual tears in her eyes, the scientist insisted.

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"That gave me the idea that oxytocin might increase tears," he added.

The hormone produced in the brain plays a major role in birth as well as in coexistence among people. It induces labor, stimulates milk production, strengthens the bond between mother and child, as well as between couples, and build trust in other people among adults.

From earlier observations, the researchers working with Kikusui knew that oxytocin is released during interactions in both dogs and their owners.

They now wanted to find out whether dogs cry when they are reunited with their humans – and that turned out to be the case!

What's more, pooches didn't shed a tear for a person they didn't know. Also, when researchers added oxytocin to the dogs' eyes, the amount of tears increased.

Dogs, the study authors say, seem to produce tears in situations that humans see as "happy."

But whether dogs also cry when they're sad remains an open question for now.