July 23, 2013
‘Love Hormone’ Oxytocin May Also Intensify Social Anxiety
Rebekah Eliason for redOrbit.com - Your Universe Online
New research indicates the love hormone oxytocin may have a dark side. Oxytocin is commonly thought of as the warm and fuzzy hormone that promotes feelings of love. It is currently even undergoing tests for use as an anti-anxiety drug. However, researchers at Northwestern Medicine have discovered oxytocin can intensify and cause emotional pain.
This study is important because reoccurring social stress is one of the leading causes of anxiety disorders and conversely positive social experiences are an important factor in overall emotional health.
Jelena Radulovic, Dunbar Professsor of Bipolar Disease at Northwestern University School of Medicine said, "By understanding the oxytocin system's dual role in triggering or reducing anxiety, depending on the social context, we can optimize oxytocin treatments that improve well-being instead of triggering negative reactions."
The Northwestern researchers are the first to link oxytocin with social stress and its propensity to increase anxiety and fear when faced with future social situations. The region in the brain responsible for these effects is known as the lateral septum and is the location of pathways used by oxytocin.
For six hours after a negative social experience, a molecule known as extracellular signal regulated kinases (ERK) is activated by oxytocin. ERK is responsible for enhancing fear by activating fear pathways that travel through the lateral septum. This discovery surprised researchers because of oxytocin's association with love and social bonding.
Yomayra Guzman, a doctoral student under Radulovic said, "Oxytocin is usually considered a stress-reducing agent based on decades of research. With this novel animal model, we showed how it enhances fear rather than reducing it and where the molecular changes are occurring in our central nervous system."
This new study was preceded by three human studies, all indicating oxytocin's more complicated nature. All of the new oxytocin experiments were performed in the lateral septum, which is the area with the most concentrated levels of oxytocin receptors in animals ranging from mice to humans.
Radulovic explained, "This is important because the variability of oxytocin receptors in different species is huge. We wanted the research to be relevant for humans, too."
This study was composed of two experiments performed on mice. The first experiment indicated oxytocin is a key factor in strengthening memories of negative social experiences. The second experiment showed oxytocin increases fear and anxiety when facing similar future stressful situations.
In experiment one, three groups of mice were placed one at a time into a cage with aggressive mice where they experienced social defeat. The first group of mice was missing oxytocin receptors in the brain, which prevented oxytocin from entering the brain's cells. The second group of mice possessed extra oxytocin receptors so they experienced a large abundance of the hormone. The third and last group functioned as a control group and had a normal number of oxytocin receptors.
Six hours after the first negative social experience, mice were placed back into cages with the aggressive mice. The group who was missing their oxytocin receptors showed no fear or indication they remembered the aggressive mice. In contrast, the mice with extra oxytocin receptors were intensely afraid of the aggressive mice and tried to avoid them.
The second experiment also exposed the same three groups of mice to aggressive mice and once again experienced social defeat. Six hours after experiencing social stress, the mice were placed in a box and received a non-painful but startling electric shock. After 24 hours, mice were placed into the same box again but did not receive an electric shock.
The first group of mice with missing oxytocin receptors showed no signs of fear when placed back into the shock box but those with extra oxytocin receptors displayed a heightened sense of fear. The control group behaved as expected by exhibiting an average fear response.
"This experiment shows that after a negative social experience the oxytocin triggers anxiety and fear in a new stressful situation," Radulovic said.
This study was published July 21 in the journal Nature Neuroscience and was funded and supported by the National Institute of Mental Health of the National Institutes of Health.