Oxytocin is affectionately known as the “cuddle hormone”, the “bonding hormone”, and the “love hormone”. It is vitally important for establishing intimacy in the brain. Several studies have shown oxytocin’s role in childbirth, social recognition, orgasm, and pair bonding. But do we know the precise role that this hormone plays? Does it cause the warm and fuzzy feelings, or is the hormone produced after the intimate event? Alternatively, is it just a hormone that’s tagging along for the ride?
To answer this question, researchers studied pup retrieval, a mammalian social behavior in which a mouse mother finds her distressed babies and returns them to their nest. Mouse pups give off ultrasonic calls, which are higher than the upper limit of human hearing when they are away from the nest. Their mothers use these sounds to locate their babies and bring them back. Neurologically, responses to these calls vary between experienced mothers and virgin mice. This retrieving phenomenon is seen primarily in mothers.
Image Source: Stephen Dalton
Researchers developed an antibody that would bind to the oxytocin receptor and found that oxytocin primarily binds to neurons, or brain cells, in the left hemisphere of the female’s auditory cortex. There was much greater receptor expression in the left auditory cortex than in the right. By binding to the part of the brain that processes sound, oxytocin masks the neural “background noise” that might hide the sound of a crying pup.
This study, recently published in Nature, shows that the brain uses oxytocin to seek out helpless babies and stop their cries by providing comfort, food, and warmth. It acts predominantly to decrease inhibition of the brain cells in the left auditory cortex, allowing maternal responses. Long-term modification of the brain also occurs, causing a snowball effect and leading to more maternal learning, behavior, and affection.
This same phenomenon was seen in virgin mice injected with excess oxytocin. These mice treated non-related pups with the same affection as mothers. Furthermore, these changes were lifelong. Even after blocking receptors on these neurons in the left auditory cortex, virgin mice still behaved in a motherly way. The researchers proposed that oxytocin receptors may be required for initiation of pup retrieval but become less important over time.
Overall, this study shows that oxytocin acts to push individuals towards a more social behavior. In the future, supplemental oxytocin may be used to treat a variety of diseases, including PTSD, social anxiety, and depression.
Feature Image Source: Cuddle by Pedro Travassos
