The biological pathway that determines how mice feel pain differs between males and females and could translate to humans leading to gender specific painkillers.
In males, immune cells called 'microglia' are involved in the development of chronic pain. Among females, however, a different immune cell, the T-lymphocyte, is key to triggering the pain state.
In the experiments, mice with chronic pain caused by nerve damage were subjected to a stimulus that would normally be perceived as a light stroking sensation. These animals register the stimulus as painful, as do humans with similar injuries. People with this condition are said to be suffering from mechanical allodynia, and it's very common.
"In males, the mice would go back to the withdrawal threshold of 1 gram, whereas in females they would remain down at 0.1 grams," says Mogil.
Speculating that another system or cell type must be involved to account for the difference between the two sexes, the team found that, in females, arresting the actions of T cells was required to achieve the same pain-relieving effect.
This suggests that, if the same is found to be true in humans, many drugs under current development could fail, as Mogil explains. "There is a great need for new painkillers and many of the compounds under development are actually working on this biological circuit that we have now shown only applies to males. The drug will fail in the clinical trials, which are, by law, half men and half women, and not help the half of the population that it could have helped."
Now that this gender difference has been identified it could lead to gender specific, or 'his n' hers' painkillers, according to Mogil.
"The idea of blue pills and pink pills for pain, I really believe that one of these years, that's actually going to be a reality!"