Estrogen and progesterone can trigger the production of pain-killing substances by special immune cells located near the spinal cord. (Image credit: theasis via Getty Images)
Experimental studies in animals have shown that the female sex hormones estrogen and progesterone may help relieve pain.
A new study in lab mice found that the two hormones work together to direct immune cells located near the spinal cord. These cells then produce their own painkillers — specifically, an opioid known as enkephalin. Opioids are released in response to nerve damage, but only in female mice, according to the study.
In the absence of injury, both male and female mice produce normal amounts of enkephalin through these specific immune cells, said study first author Elora Midawein, a postdoctoral fellow at the University of California, San Francisco (UCSF). “After injury, however, levels increase in females but not in males,” she added.
Thus, pain-producing immune cells known as regulatory T cells (Tregs) block pain signals transmitted by neurons in the spinal cord, thereby preventing them from reaching the brain.
“We didn’t expect that these [Treg] cells would be heavily involved in pain perception at all, and especially not in such a sex-specific manner,” Midawine told Live Science. “That surprised us for a while, and we were even skeptical about these findings at first.”
In the future, this research could help shed light on sex differences in pain perception in humans, as well as how pain perception changes during pregnancy and menopause, when estrogen and progesterone levels in the body fluctuate significantly. Ultimately, the work could point to new approaches to pain treatment, the study authors say.
Immune cells in pain perception
Numerous studies point to differences in how men and women experience pain.
In general, research shows that women have a higher sensitivity to pain than men, meaning they feel more intense pain when their pain receptors are activated. They have also been found to have lower pain thresholds, meaning less stimulation is required to activate the receptors.
These patterns are observed across a variety of pain types, including those caused by extreme temperatures, mechanical pressure, and inflammation. They have also been documented in studies of a variety of male and female animals, suggesting a biological basis.
Women also report higher rates of chronic pain than men. Some of the differences in pain may be due to cultural factors related to how each gender is socialized about pain and how likely they are to seek help. However, research also points to biological differences in how pain is processed in men versus women.
In the new study, Midawine, Dr. Sakin Kashem, an assistant professor of dermatology at the University of California, San Francisco and a co-author of the study, and their colleagues sought to better understand how immune cells might interact with the nervous system to alter pain signaling and whether there are any sex differences in this process. Previous work from other labs has suggested that T cells play a role in pain perception in female mice, while in male mice, pain relies on a different type of cell.
Tregs are a type of T cell, so scientists wondered what role they play in the overall context.
“We started looking at Tregs because they are inhibitors of the immune system,” Kashem told Live Science. “So the question became, 'What if we just removed them?'
An unexpected difference between the sexes
In their new study, published Thursday (April 3) in the journal Science, the scientists focused on Tregs located in the meninges, the membranes that wrap around and
Sourse: www.livescience.com
