A study conducted by Japanese researchers revealed that dogs get emotional and cry when they reunite with their owners because of the excitement and joy.

A team led by researcher Takefumi Kikusui investigated whether not only humans but also their four-legged friends sometimes cry when they are emotionally overexcited.

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

"That gave me the idea that oxytocin might increase tears," Kikusui 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, and can also strengthen couple bonds and build trust in other people among adults.

From earlier observations, the researchers working with Kikusui also 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 master or mistress.

That was the case, while they did not shed tears for a person they didn't know. Also, when they added oxytocin to the dogs' eyes, their tears increased.

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

The question remains open as to whether dogs also cry when faced with negative emotions.