Many people know oxytocin as “the love hormone” or the “cuddle hormone.” It has already been implicated in creating a bonding effect between mothers and children, as its release is heightened during labor, childbirth, and breast feeding. Recent research may have identified another function of this hormone; pain relief and modulation.
How might oxytocin play a role in pain relief?
Oxytocin is only produced in the hypothalamus. It is then released into the bloodstream by the posterior pituitary gland. However, the pituitary gland has two types of neurons, though only the larger neurons play a role in bloodstream release. The smaller neurons are connected to the spinal cord and brainstem; these spinal projections may play a role in pain relief. Rats with elevated levels of oxytocin in their bloodstreams did not react as strongly to having their inflamed paws touched, whereas the rats that had inhibited release of the hormone experienced less analgesia. While this result was consistent in both mechanical and thermal stimulation, it was only true for inflammatory pain. Oxytocin mediated pain relief was not shown in a neuropathic pain model. No effects were observed in naïve animals, suggesting that sensitization (eg, an injury), must first happen.
These findings suggest that oxytocin plays an inhibitory role in the pain system; its pain blocking effects would be similar to endorphins. Curiously, there is some overlap between other functions of oxytocin and endorphins. Both are released during sex and orgasm, as well as while exhibiting certain maternal behaviors.
What still needs to be done?
First, this study was conducted in rats. It is possible that humans have different connections between the spinal cord and oxytocin producing cells. The effects of the hormone may be stronger, weaker, or not present at all. As a result, further preclinical trials must first be completed.
It is also unclear how the system is activated. While many C-fibers are involved in pain sensation, there is a small subset involved in “pleasant touch” sensation. It is possible that these neurons are responsible for transmitting the signal that activates part of the oxytocin system, specifically the part involved in bonding. This supports a hypothesis that pleasant touch C-fibers are involved in pain relief. Furthermore, the mechanisms of communication between hypothalamic neurons and spinal neurons also must be clarified.
Despite the work that needs to be done, this research can open an entire new area of pain treatment and management. It is also a reminder that pain is not purely sensory. Rather, it affects many of the body’s systems, including the endocrine system.
Author’s note: For the original research mentioned in this article, please see:
Eliava, M., Melchior, M., Knobloch-Bollmann, H., Wahis, J., Da Silva Gouveia, M., Tang, Y., . . . Grinevich, V. (2016). A New Population of Parvocellular Oxytocin Neurons Controlling Magnocellular Neuron Activity and Inflammatory Pain Processing. Neuron. Retrieved March 15, 2016.
Editors: Daryn Dever and Shreya Singireddy