Women suffer from a higher incidence of chronic and inflammatory
pain conditions such as fibromyalgia and osteoarthritis. While morphine
continues to be one of the primary drugs used for the treatment of
severe or chronic pain, it is often less effective in females.
A female brain's resident immune cells are more active in regions
involved in pain processing relative to males, observed a recent
study by Georgia State University researchers.
‘When the brain's resident immune cells were blocked, female response to opioid pain medication improved and matched the levels of pain relief normally seen in males.’
The study, published in the Journal of Neuroscience
that when microglia, the brain's resident immune cells, were blocked,
female response to opioid pain medication improved and matched the
levels of pain relief normally seen in males.
"Indeed, both clinical and preclinical studies report that females
require almost twice as much morphine as males to produce comparable
pain relief," said Hillary Doyle, graduate student in the Murphy
Laboratory in the Neuroscience Institute of Georgia State. "Our research
team examined a potential explanation for this phenomenon, the sex
differences in brain microglia."
In healthy individuals, microglia survey the brain, looking for
signs of infection or pathogens. In the absence of pain, morphine
interferes with normal body function and is viewed as a pathogen,
activating the brain's innate immune cells and causing the release of
inflammatory chemicals such as cytokines.
To test how this sex difference affects morphine analgesia, Doyle
gave male and female rats a drug that inhibits microglia activation.
"The results of the study have important implications for the
treatment of pain, and suggests that microglia may be an important drug
target to improve opioid pain relief in women," said Dr. Anne Murphy,
co-author on the study and associate professor in the Neuroscience
Institute at Georgia State.
The research team's finding that microglia are more active in brain
regions involved in pain processing may contribute to why the incidence
rates for various chronic pain syndromes are significantly higher in
females than males.