The same loyalty chemical is found in human brains, and scientists said the research could provide insight into treating human grief and separation.Working with mouse-like rodents called prairie voles, scientists have found that close monogamous relationships alter the chemistry of the brain, fostering the release of a compound that builds loyalty, but also plays a role in depression during times of separation.
The scientists found that after four days away from their mates, male voles experienced changes in the emotional center of their brains, causing them to become unresponsive and lethargic. When given a drug that blocked the changes, however, lonely voles emerged from their funk.
The study might also "shed light on why couples remain in relationships that are bad for them"
Others call for scrutiny in anthropomorphizing voles. Read the whole thing.
P.S. the voles were killed to examine their brain chemicals.