'Love hormone' doesn't always lead to happily ever after, researchers find

It has long been thought that oxytocin was responsible for positive social behavior, leading to it being dubbed the 'love hormone,' but new research suggests it's more complicated than that.

Mice [Illustrative] (photo credit: INGIMAGE)
Mice [Illustrative]
(photo credit: INGIMAGE)
The coronavirus lockdown has pitched couples into each other's company for extended periods of time. Some are closer than ever while others are on their way to the divorce courts. Life is complex, but so is the effect of oxytocin, a neuromodulating peptide produced in the brain which can be responsible for creating bonds - or for aggression, depending on the context.
That was the conclusion researchers at the Weizmann Institute in Rehovot, Israel, came to after studying the effect of increasing oxytocin levels in mice in semi-natural habitats in comparison with mice living under lab conditions.
Prof. Alon Chen’s lab group in the Institute’s Neurobiology Department was able to use optogenetics to turn specific neurons in the brain on or off using light. The group developed a lightweight, wireless device to allow them to activate nerve cells by remote control.
Aided by optogenetics expert Prof. Ofer Yizhar within the same department, the group added a protein developed by Yizhar into the mice's moxytocin-producing brain cells. According to the Weizmann Institute, when light from the remote controlled device touched those neurons, they became more sensitized to input from other brain cells.
Having developed this highly precise method of manipulating oxytocin levels, they were able to apply it in different settings to explore how the interplay between environment and brain chemistry worked.
Past research on neurotransmitters has taken place in strictly controlled, artificial lab settings. While this setup means that researchers can limit the number of variables affecting behavior, recent studies have suggested that placing the mice in semi-natural settings full of various stimuli is a much better way of researching natural behavior, which in turn can give greater insight into the application of findings to humans.
An ongoing study carried out over the last eight years, led by research students Sergey Anpilov and Noa Eren, and Staff Scientist Dr. Yair Shemesh in Prof. Chen’s lab group, and published in Neuron, did just that: manipulating the oxytocin levels in mice under lab conditions and in semi natural conditions to see how the results might differ.
“Our first goal,” said Anpilov, “was to reach that ‘sweet spot’ of experimental setups in which we track behavior in a natural environment, without relinquishing the ability to ask pointed scientific questions about brain functions.”
Shemesh added that “the classical experimental setup is not only lacking in stimuli, the measurements tend to span mere minutes, while we had the capacity to track social dynamics in a group over the course of days.”
What they found was that the effect of oxytocin depended upon the setting.
It was long thought that the neuromodulator was responsible for mediating positive social behaviors, leading to oxytocin being dubbed the 'love hormone,' but conflicting results had led some to suggest an alternative: social salience.
The hypothesis in this case stated the oxytocin amplified social cues to result in increased positive and negative behavior, depending upon the conditions at the time.
Within the semi natural setting, as the levels of oxytocin in their brains were gradually increased, the mice first showed increased interest in each other, but this soon spilled over into aggressive behavior. By contrast, as the oxytocin level increased under lab conditions, the mice showed less aggressive behavior.
“In an all-male, natural social setting, we would expect to see belligerent behavior as they compete for territory or food,” says Anpilov. “That is, the social conditions are conducive to competition and aggression. In the standard lab setup, a different social situation leads to a different effect for the oxytocin.”
The findings could modify the way oxytocin is used to treat a variety of psychological conditions in humans, including social anxiety, autism and schizophrenia.
“Oxytocin is involved, as previous experiments have shown, in such social behaviors as making eye contact or feelings of closeness,” says Eren, “but our work shows it does not improve sociability across the board. Its effects depend on both context and personality.”
The implication is that if oxytocin is to be used therapeutically, a much more complex, nuanced view of its effects needs to be taken into account.
“If we want to understand the complexities of behavior, we need to study behavior in a complex environment," Eren added. "Only then can we begin to translate our findings to human behavior."