It has long been assumed that pain is treated equally by everyone. However, more and more studies suggest that this is not the case at all. Overall, women are more sensitive to pain than men. New work led by Canadian researchers takes a closer look at these biological differences leading to these sex-based differences.
Women are more affected by the burden of chronic pain. They are indeed more likely than men to report low back, orofacial, cervical and neuropathic pain. In addition, twice as many women report migraines or common headaches.
In the quantitative assessment of experimentally induced pain, women also show greater pain sensitivity than men across several noxious modalities, including mechanically induced pain , electrically, thermally and chemically. However, we still don't know exactly why. Some studies suggest that the female body has greater nerve density or that fluctuations in female hormones could amplify the body's perception of pain.
In new work published in the journal Brain, Dr. Annemarie Dedek and her team at Carleton University closely analyzed the nerve receptors located in the tissues of the spinal cord .
The spinal cord is indeed presented as a kind of intermediary in the way of pain. When neural sensors in muscles, skin, organs or joints detect a potentially dangerous sensation for the body, signals are sent to the spinal cord. This in turn activates other nerves that send signals to the brainstem and the brain. Everything is obviously done in a fraction of a second.
This study had two major advantages over previous research. First, it included female subjects . And second, it included human subjects .
First, note that there is a specific type of protein that lives in our spinal cord. This is known as brain-derived neurotrophic factor, or BDNF abbreviated. It plays an important and complex role in pain processing, amplifying signals over short periods of time and doing the opposite over the long term. This is nothing new. This gene was in fact discovered forty years ago and other studies have already studied its role in the perception of pain. However, as stated above, most previous studies have focused on male mouse subjects, often rats.
That being said, by analyzing the tissues of the spinal cord in the laboratory, the researchers then found that this gene BDNF was essential for amplifying spinal cord pain signaling in male humans and male rats. Females and rats, however, were not affected by this factor. In other words:male and female bodies, and the BDNF gene in particular, really process pain differently . But why?
“We conclude that this sex difference in response to BDNF is hormone-mediated “, write the authors. This is consistent with previous studies that attribute women's pain to their higher estrogen levels. This hypothesis is also supported by the results of a separate experiment in which the researchers removed the ovaries from several of the female rats involved in this study. The previously observed differences between the sexes had indeed disappeared.
This is the first time that sex-based differences in pain signaling have been reported in the spinal cord. More research will of course be needed to better understand how these biological differences cause men and women to process pain so differently.
Nevertheless, the importance of this discovery should not be underestimated. Indeed, most analgesics available on the market are not interested in this sexual dimorphism. This new discovery could thus lay the foundations for the development of new, more suitable treatments to help people with chronic pain.
