What was previously known about chronic pain was re-evaluated by a new study that confirms different immune cells are responsible for its transmission in male and female mice.
The study was jointly conducted by McGill University, the Hospital for Sick Children and Duke University. The findings pinpointed the answer as to why some treatments for chronic pain have failed with a certain segment of the population.
Previously, an increasing amount of evidence held that pain is transmitted from the sites of inflammation or injury via microglia throughout the entire immune system.
In the United States, one out of four citizens reported experiencing chronic pain, according to reports coming from the National Institutes of Health. Chronic pain is more often the cause of ailment than cancer or diabetes or coronary heart disease combined.
How women and men feel pain was thought to be a leveled field of research. Yet, according to Dr. Jeffrey Mogil from the McGill University:
“Research has demonstrated that men and women have different sensitivity to pain and that more women suffer from chronic pain than men, but the assumption has always been that the wiring of how pain is processed is the same in both sexes”.
According to the new study conducted on mice, that is not the case. Pain is not processed the same way for both males and females.
The research team severed two sciatic nerve branches in the mice’s hind paws to inflict pain. The mice were an equal number of male and female individuals, all healthy. In order to relief the pain, the researchers injected each of the mice with a microglial inhibitor drug, seven days after the pain was inflicted.
The microglial inhibitors were three of the most common used for chronic pain relief. All three were found to successfully reverse pain sensitization in the male mice. However, it was a different story with the females.
Although the levels of pain of both male and female mice were similar, females didn’t react at all to any of the three drugs that inhibit the microglial cells.
To this extent, the researchers concluded that BDNF signals sent by the microglia throughout the immune system is crucial for pain hypersensitivity with male mice. For the female mice it is clear that another system is responsible for this mediation.
Researchers suspect that instead of the microglial cell, hypersensitivity to pain depends on the T-cells of the immune system. Thus far, it is unclear what the mechanism is and more research is required.
The joint study features in the Nature Neuroscience journal.
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