January 10, 2009
Brain Difference For Pain Between Males And Females
Women need more morphine to relieve pain and the reason might be fewer mu-opioid receptors in female brains.
"Opioid-based narcotics (such as morphine) are the most widely prescribed therapeutic agents for the alleviation of persistent pain; however, it is becoming increasingly clear that morphine is significantly less potent in women compared with men. Until now, the mechanism driving the phenomenon was unknown," said Anne Murphy, Ph.D., a Georgia State Professor of Neuroscience and member of the Center for Behavioral Neuroscience, who conducted the research with Dayna Loyd, Ph.D.
Murphy recently solved the mystery with findings printed in the December issue of The Journal of Neuroscience that show that previously reported differences in morphine's ability to block pain in male versus female rats are most likely due to sex differences in mu-opioid receptor expression in a region of the brain called the periaqueductal gray area (PAG).
Located in the midbrain area, the PAG plays a major role in the modulation of pain by housing a large population of mu-opioid receptor expressing neurons. Morphine and similar drugs bind to these mu-opioid receptors analogous to a 'lock and key' and, ultimately, tell the brain to stop responding to pain signals to the nerve cells resulting in the reduced sensation of pain.
Using a series of anatomical and behavioral tests, Murphy and Loyd were able to determine that male rats have a significantly higher level of mu-opioid receptors in the PAG region of the brain compared with females. This higher level of receptors is what makes morphine more potent in males because less drug is required to activate enough receptors to reduce the experience of pain. Interestingly, when they used a plant-derived toxin to remove the mu-opioid receptor from the PAG, morphine no longer worked, suggesting that this brain region is required for opiate-mediated pain relief.
I wonder what behavioral difference this causes in the daily lives of men and women and why this was selected for.
Perhaps it relates to the ability to suppress pain during flight or fight circumstances? Those receptors aren't there to detect plant products, after all, but instead natural opiates.
Speculating freely on a subject I know nothing about:
Does this translate into higher pain susceptibility for women? If so, I can see where a higher pain sense can make it more likely one survives by preventing one from doing unwise things.
Men, on the other hand, did things like get in fights and hunt large game. In those situations, a too sensitive pain response might have been too distracting. You need to stop or get away from whatever it is that's hurting you before you can worry about your injuries.
PS: Do male rats fight for mates?
Female are more susceptible to pain due, in part, to the lack of testosterone.
Males that changed sex, reported more susceptibility to pain as soon as they start to take female hormones and male hormones suppressors.
Xenophon Hendrix is probably right, higher pain susceptibility deter many women from going out and do risky things.
This is useful, as they are needed to give birth and raise the children.
My job at a hospital was on a combo unit that was for adult females and pedis, but I was occasionally pulled to other units, where I'd care for male patients. Although we'd studied pain management, and were taught that fear often elevated the perception of pain, I noticed something that wasn't taught that I 'coined' "first real pain".
First time surgeries usually seemed the most difficult to manage pain-wise, no matter the age or gender. Children with laproscopic appendectomies, or older men or women with laproscopic gall bladder surgeries reacted like they were in as much pain as a woman that's had a few c-sections in her past, and was currently recovering from a combination hysterectomy/bladder/tummy-tuck, which was much more invasive. I believe that in addition to getting past the shock of serious pain like surgery, learning how to move post-op helped make the repeat surgeries easier to handle.
My current husband has a few surgeries and broken bones in his past, and handles pain MUCH better than my ex did, who I saw writhing in pain after his first surgery, even though he fancied himself a "tough" guy. Another thing I noticed the few times I cared for men post-op is that they act completely different around their mothers/wives/daughters than they did when other males were round, especially if they knew those males from their personal or professional lives. I sometimes had difficulties getting some post-open heart males to walk if just their wives were around, but if a work buddy or male neighbor showed up, they 'grinned and beared it'.
One last thing about my limited experiences with male patients and pain: For the most part, soldiers and cops usually handled pain better, whether male or female.
Having explained that, and mostly working with post-op females, it seemed to many of us working that unit that women handled pain better than men, which is why I found this study interesting. If I find myself working post-op, or other painful specialties in the future, I'm going to pay attention to dosages required to control pain between the genders