Sex differences in brain activity alter pain therapies

Chronic pain is the most common human health problem, it is thought to affect more than 1 in 4 people worldwide, with higher incidence occurring in older populations.

It is well-established that chronic pain affects more women than men. One might reasonably conclude that this is because a number of chronic pain illnesses, such as endometriosis and menstrual pain, can only occur in women

Now, researchers at Georgia State University have discovered a female brain’s resident immune cells are a lot more active in areas linked to pain processing compared to males’. And when these cells, known as microglia, are blocked women respond to opioid pain relief medication -like codeine and morphine- much better, with results matching those found levels found in men.

For their investigation, senior author Anne Murphy, an associate professor who heads a pain research group in the Neuroscience Institute at Georgia State and colleagues chose to study morphine, the primary drug for relieving severe or chronic pain.

The researchers note how it is often the case that female patients require much more morphine than male patients to achieve similar analgesic effects.

“Indeed, both clinical and preclinical studies report that females require almost twice as much morphine as males to produce comparable pain relief,” says first author Hillary Doyle, a graduate student in Murphy’s research group.

“Our research team examined a potential explanation for this phenomenon, the sex differences in brain microglia,” she adds.

“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.

The microglial revolution is relatively young; Nature only reported in 2012 that they were being discovered to be more than “passive sentinels.” But it’s moving fast. We now have regular experiments in which they’re being knocked out in mice, and a method by which the same experiment could be performed on human microglia is likely not far behind.

Once that happens, microglia knock-out or alteration therapies could be part of normal treatment for chronic pain, particularly in women, and microglial reaction could help construct better pain responses for various medications. Good news indeed.

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