A new study conducted by a team of researchers at the Weizmann Institute of Science and published in the Nature Neuroscience scientific journal reveals new mechanisms by which oxytocin influences our behavior and the different ways it affects male and female behaviors.
The study was led by Dr. Yizhak Sofer and supervised by Professor Tali Kimchi, a researcher in the neurobiology of social behavior at the Weizmann Institute of Brain Sciences Department. "Oxytocin is a neuromodulator," Kimchi explained. "It’s secreted in the brain by nerve cells in the hypothalamus, where it acts as a neurotransmitter that can activate other brain regions.”
“It is also released into the blood and acts as a hormone. This hormone is considered a female hormone – and plays a critical role in maternal behavior, from uterine contractions during childbirth to milk release during breastfeeding and the mother-child bond. Its role in males is less studied, but likely also plays a role in enhancing paternal behavior."
According to Kimchi, oxytocin regulates brain areas related to behavior by modulating brain activity. "It activates many areas associated with our social-emotional state and motivation by regulating the release of another neurotransmitter, dopamine," she added.
"We know that oxytocin can promote positive social interactions like strengthening the parent-child bond, but we also know from previous studies it can exacerbate behaviors considered negative, such as competitiveness, territorial behavior, and aggression. It is also responsible for regulating stress levels and likely has a significant role in regulating many brain activities that we still don’t to a deep level."
In the study, Kimchi and her team aimed to examine the differences in oxytocin expression between males and females. "Oxytocin is expressed at very high levels in both males and females, with no difference in the number of cells between the sexes," she explained. "We knew from the literature that these cells are responsible for aggressive behavior in males, but the topic has yet to be studied in females."
However, they first had an issue to overcome. "Aggressiveness traits among female lab mice have disappeared over the years due to the selection processes lab mice underwent," Dr. Sofer explained.
"For example, in nature, wild female mice are aggressive. If an intruder enters their territory, they will attack. To solve this issue, we held the study on wild mice and, via genetic manipulation, increased the oxytocin cell activity in their brains on one hand and decreased the number of oxytocin-producing cells on the other.
"From there, we wanted to examine whether this plays a different or similar role between males and females in their one-on-one and group behaviors,” he added.
“To achieve this, we placed a group of mice in an arena simulating their natural territory and allowed them to interact with each other, leading to the formation of a social hierarchy, i.e., who is more dominant in the group and who is less so. We then analyzed the data to examine aggressive behavior and whether a hierarchy was formed or not," he said.
What did you discover?
"We found that oxytocin cells play a role in triggering aggressive and territorial behavior in one-on-one interactions,” Kimchi explained. “This effect was mainly seen in females: when we activated these cells, they became more aggressive toward intruders and even toward unrelated mouse pups.
“We also found oxytocin mediates hierarchy formation, a finding that was more prevalent in females. Conversely, reducing the number of oxytocin cells in females led to an unstable hierarchy – we couldn’t determine who was dominant and who wasn’t. However, reducing these cells in males didn’t result in the loss of the ability to create a hierarchy,” she added.
In simpler terms, "oxytocin is crucial for hierarchy formation in females but acts as a regulator for the intensity of the hierarchy in both males and females. In other words, it has a more subtle role in males. The assumption is that the male hormone testosterone and other neural circuits likely play a more significant role in males. In contrast, in females, the factor of oxytocin cells is more critical."
How will this study help in the future?
"These findings may advance the understanding of oxytocin's role in social contexts and even offer new insights into the biological mechanisms of psychiatric disorders that include a social component, such as autism spectrum disorders, Alzheimer's, and Parkinson's, as well as disorders related to social anxiety and increased aggression.”
“Understanding oxytocin’s role in our neurology will allow a deeper understanding of social dynamics, which we consider the foundation of human society and what shapes and regulates it."