It’s an age-old debate, who feels more pain, men or women? Scientists at McGill University have taken us one step closer to answering this question with a study using mice. Jeff Mogil and his team have discovered that the biological pathway that causes chronic pain is completely different in male and female mice. If the same is found to be true in humans it could lead to gender specific, or ‘his n’ hers’, painkillers in the not too distant future… You can listen to the full interview with the Naked Scientists here.

Jeff – We found that a major biological pathway involved in pain processing that’s been studied for the last 15 years or so by researchers around the world is actually only relevant and valid in male mice. And in fact it appears not to be used at all in female mice who instead appear to be using a completely different biological pathway.

Tom – What did you actually do in these experiments?

Jeff – Well we were studying a common and important symptom of chronic pain called mechanical allodynia. Mechanical allodynia is when a stimulus that should be perceived as touch is actually perceived as pain. 

Tom – Could you give an example of what that would be in a human?

Jeff – Everyone has had mechanical allodynia. If you’ve ever had sunburn – let’s say you’ve sunburnt your back and I came by and sort of gave you a playful slap on your back. Under normal circumstances that wouldn’t be painful, but if you had a sunburnt back you would go through the roof and that in fact is mechanical allodynia. Before injury mice will tolerate about a gram of force applied to their hind paw. After the injury, they will now withdraw form fibres that are 0.1 or maybe 0.2 grams of force. And then we looked at how we could block that mechanical allodynia, by blocking a cell in the spinal cord called microglia. In males what we would see is that the withdrawal thresholds would go right back up to 1 gram, whereas in females they would stay down at 0.1 grams. There has to be another system that is picking up the slack and performing the same function in female mice. In our study, we preliminarily identified another system involving T-cells, which are also immune cells, but a completely different type of immune cell than microglia.

Tom – And you think this potentially could translate to humans?

Jeff – I think our default assumption is always that the biology of pain in mice and humans is likely very similar until proven otherwise. Now of course there are always species differences, but in general biomedicine only works because these species differences are few and far between. 

Tom – So you’ve shown this in mice and this potentially could be the same in humans, but what does this actually mean?

Jeff – There’s a lot of drug development going on – there’s great need for new analgesics because the analgesics that we have available either don’t work very well or have really terrible side effects. So, there’s a huge need for new analgesics in the world, new painkilling drugs and there are lots of people trying to develop them. Many of the compounds that are under development are actually working on this biological circuit that we have now shown only applies to males. That of course is a problem because what that would predict is that the drugs that are going to be developed will work in men, it’s just that we have no reason to believe that they will work in women. The clinical trial is going to come along, which by law are half men and half women and what might happen is that if the drug works in the men but doesn’t work in the women, overall it’s going to look like the drug doesn’t work and that clinical trial is going to fail. The drug will never get on the market, it will never help the half of the population that it could’ve helped and hundreds of millions of dollars will have been wasted and no-one will really know why. The other thing is that while there’s a whole biological circuit that applies to females and not males, then eventually drugs might come out of that which work on women and not men. So, you can think of the idea of blue pills and pink pills for pain. I really believe that one of these years that’s actually going to be reality.

Part of the ‘Throwback Thursday’ series – you can find all of the highlighted interviews here.