In February, love is in the air … and the lab. New research with animals is helping scientists learn more about how love develops and endures, how feelings of love affect us mentally and physically, and the specific roles of love-related chemicals including oxytocin and dopamine.
The Power of Touch
It’s not just our imagination that touch is an essential part of bonding and love—there’s actually scientific proof.
A 2021 study found that humans deprived of intimate touch from close family members and partners felt higher levels of anxiety and loneliness, and other studies have found that touch enhances bonding in couples.
A new study by a team of researchers at Columbia University, University of Pennsylvania, and Rutgers University found that directly stimulating sensory cells (Mrgprb4 neurons) on the backs of mice, which is an important area for social touch in mice, can cause their brains to release dopamine, a neurochemical associated with reward.
By activating those cells using light, the researchers were able to induce social bonding behaviors in female mice even when other mice were not present. The mice also chose to spend more time in the areas of their environment where the cell stimulation occurred, indicating that they found the experience pleasurable.
When the team genetically disabled the Mrgprb4 cells, the mice no longer responded positively to social approaches from other mice. The discovery could lead to new ways to use touch-based therapy as a treatment for anxiety, stress, and depression.
Love’s Heart-Healing Properties
You’ve heard of people dying of a “broken heart,” but actually the reverse may be true.
A study of zebrafish at Michigan State University has shown that the “love hormone” oxytocin can trigger heart repair by stimulating stem cells from the heart’s outer layer (epicardium), eventually prompting the growth of cardiomyocytes, the muscle cells that cause heart contractions.
In the study, researchers tested the hearts of zebrafish, which are known for being able to regrow their own organs. Three days after injury to the heart due to freezing, the bodies of the zebrafish ramped up production of oxytocin to levels up to 20 times higher than normal. The oxytocin moved to the epicardium of the zebrafish and triggered a healing process that replaced the heart cells that had been damaged or lost.
The finding could be used to develop new treatments for heart regeneration after a heart attack. A heart attack often wipes out large numbers of cardiomyocytes, which can’t regenerate on their own. The new discovery could lead to a therapy in which epicardium cells are engineered to rebuild other types of heart cells.
A Surprising Tendency of Testosterone
Testosterone is associated with strength, libido, and aggression. But researchers at Emory University have found that testosterone can also foster more gentle reactions, depending on the social context.
To test the effects of testosterone, the researchers used Mongolian gerbils, which are generally thought to be monogamous and which raise their offspring together. Using bonded pairs, the team waited until the female became pregnant, then injected the male with testosterone.
Male Mongolian gerbils typically cuddle with their pregnant mates, and the research team expected the influx of testosterone to reduce or eliminate the cuddling behavior, but instead, the male gerbils became even more cuddly. In addition, the testosterone injection caused a concomitant increase in oxytocin activity in the brains of the male gerbils.
In another test, the bonded female was removed from the environment and a foreign male was introduced to the testosterone-boosted gerbil. Instead of attacking or avoiding the stranger, as it would ordinarily do, the gerbil was more friendly. After a second testosterone injection, however, the male gerbil became more aggressive.
The experiment showed that social environment may play a stronger role in shaping reactions than the testosterone itself, though the testosterone helps the animal rapidly adapt its behavior to match the social context. The team hopes the discovery will lead to other studies of how testosterone and oxytocin interact in other species, including humans.
A New Look at Oxytocin
Oxytocin is often referred to as the “love hormone,” and for good reason. Many studies have shown that oxytocin fosters social connections and triggers feelings of pleasure, trust, and generosity. But a new study with prairie voles at the University of California, San Francisco casts doubt on the necessity of oxytocin in forming love bonds.
Prairie voles, like Mongolian gerbils, form pair bonds. To test the role of oxytocin in this bonding, researchers did an experiment designed to disrupt pair bonding. They removed fertilized eggs from female prairie voles, edited the genes to neutralize the effects of oxytocin, then implanted the eggs into different females.
The team was expecting that the oxytocin-neutralized offspring would not exhibit the same pair-bonding tendencies as normal animals, but in fact the opposite was true. Despite lacking oxytocin, the pups grew up normally, formed pairs, and nurtured their own offspring.
Repeated experiments confirmed the effects, leading researchers to realize that pair bond formation does not rely solely on oxytocin, though it may play a significant role.
Science alone can’t explain love in all its complexity, but new studies have provided important insight into how it works on a biological and chemical level, and how those discoveries might be used to help heal and strengthen the hearts and minds of humans.
