There’s another meaning to those lyrics, “You ain’t nothing but a hound dog, crying all the time”. Researchers say they’ve found that dogs produce tears when reuniting with their parents and nursing pups, in a new study. And they’ve linked all the blubbering to levels of the “bonding hormone” oxytocin, the hormone associated with love.
Takefumi Kikusui, a co-author of the study at Azabu University, told the Guardian that he has two standard poodles, one of which was pregnant six years ago. He noticed how the dog’s eyes were teary when nursing her puppies. “That gave me the idea that oxytocin might increase tears,” he said.
He explains that they previously observed oxytocin releases in dogs and parents when they interacted, and so carried out a reunion experiment. The experiment, published in the journal Current Biology, is believed by Kikusui to be the “world first” to demonstrate that positive emotion stimulates tear secretion in a non-human animal and that oxytocin functions in tear secretion.
According to the study, when reunited with their people, the dogs’ tear volume increased significantly. Scientists compared it to the volume when they reunited with a familiar non-parent. As well, if the scientists added a solution of oxytocin to the animal’s eyes, the tear volume increased. “We found that dogs shed tears associated with positive emotions,” Kikusui said. “We also made the discovery of oxytocin as a possible mechanism underlying it.”
The New Study
The researchers conducted the Schirmer tear test (to determine whether the eye produces enough tears to keep it moist) on 22 dogs. They compared a dog’s tear volume before and after being away from its parent or someone they knew. The separation lasted between five and seven hours. They placed a piece of paper under the dog’s eyes to gather the tears, and then the researchers measured them.
As part of the study, humans also rated their photos of dogs with or without artificial tears. According to the study, humans gave more positive scores to the photos of dogs with artificial tears. The researchers say this suggests emotionally driven tears in dogs can help human-dog communication. However, questions still remain over whether dogs can use tears to communicate with each other.
The Role of Dogs’ Tears
Researchers explained the outcome of the study: “Unlike any other animals, dogs have evolved or have been domesticated through communication with humans and have gained high-level communication abilities with humans using eye contact … Through this process, their tears might play a role in eliciting protective behavior or nurturing behavior … resulting in the deepening of mutual relationships and further leading to interspecies bonding”.
So not only hound dogs do all the crying…
