Researchers at UAB find fascinating differences in how men and women process pain

(Video Above: Researchers at UAB find differences between how men and women experience pain)

By Donna Cope

Robert Sorge and medical colleagues believe men and women experience pain differently and that women suffer chronic pain more often than men.

Sorge may have discovered the reason.

The University of Alabama at Birmingham researcher and assistant professor in the Department of Psychology delivered groundbreaking findings in Nature Neuroscience online. In his study, Sorge and colleagues at UAB and in Canada studied male and female mice, whose pain systems mimic humans. Sorge found that the sexes use different immune cells to process chronic pain, indicating that different therapies may be needed.

That data is critical, since it is estimated that about one third of Americans have pain that is considered “chronic,” ranging from mild to excruciating and lasting longer than six months. An international study of 85,000 people showed that 45 percent of women and 31 percent of men have chronic pain. Women tend to have a lower sensitivity to pain, which supports the research of Sorge. Backache is among the most common pains, while young people commonly experience more pain from exercise.

“It is imperative to look at both males and females in research,” said Sorge, who earned a Ph.D. in psychology at Concordia University in Montreal in 2006. “It’s really notable that most research is done on male animals to model a 70 percent female population. There’s ample evidence there are differences in pain in males and females.”

Sorge and his colleagues conducted research unlike most previous studies. Their experiments used male and female mice. For years, researchers avoided studying females, Sorge suggests, under the supposition that female hormonal cycles could skew results.

Examining differences

Most existing research shows men and women have different sensitivity to pain. The assumption has been that a common pain circuit exists in both sexes, but is altered in women by estrogen. Sorge and his colleagues working in labs at UAB and in Canada found this assumption may be false.

“We looked at immune systems and how immune system receptors may change susceptibility and sensitivity to chronic pain,” said Sorge. “We found that some immune cells or receptors work differently in males and female mice.”

Now, researchers know that the immune system does more than fight off infection: It works with the brain to express pain. Some cells are critical for pain processing. When activated by injury such as inflammation or nerve damage, the cells release chemicals that reach neurons in the spinal cord to communicate the pain sensation. Sorge’s findings show this process only occurs naturally in male mice.

His research suggests a completely different part of the immune system – T cells – are responsible for releasing these same chemicals and the same signals in female mice. Sorge’s study found that females are able to use the male system when the female system is unavailable, or when high levels of testosterone are present. The results indicate that male and female mice have access to both pain reaction systems, but each sex preferentially uses one system over the other.

Critical Mandates

The National Institutes of Health recently mandated the use of female animals and cell lines in preclinical research.

Sorge predicts major changes on the horizon in the treatment of pain, including tailoring medicines and dosages according to a patient’s sex. With the lowered cost of genetic screening making testing available to more patients, Sorge believes more doctors will use this testing to check for predispositions to genetic causes of pain.

“The future of pain medicine is to look at the genetic makeup of an individual, because there are genetic causes of pain,” Sorge said. “Use of pain medicines is a very individual thing. With genetic testing, doctors will have the ability to figure which medicines will best treat a particular patient – depending on whether they are female or male – and also figure the correct dosage, based on their genetic makeup.”