On December 6th, 2015 we learned about

Progress on picking which people feel pain

Pain is very good at its job. The nerve signal from an injury to your brain is a powerful influence on our behavior, helping us avoid more serious damage to our bodies. While our responses to painful stimuli aren’t universal, it’s notable that only a handful of people on the planet are known to truly be unable to experience pain. Since it’s often easier to learn about how something works by looking at when it doesn’t, these painless people have been a great help to researchers in understanding our nervous system. Recent research is looking to better turn pain off for people with too much, while at the same time possibly enabling pain for those that can’t feel it.

Isolating the ion channels

By studying the nervous systems of people with congenital analgesia, scientists have honed in on a particular ion channel in nerve cells. A genetic mutation prevents these Nav1.7 channels from ever developing, leaving the nerve cells no way to be activated by sodium as they do in most people. While avoiding pain is something that guides many of our actions, this condition is dangerous to live with, especially for children who haven’t learned what they need to beware of to avoid injury. Babies especially will bite their extremities and lips until they’re bleeding, as their body sends no signal to their brain to stop. This isn’t to say that they feel nothing, as touch sensations still function, but the reflexes to withdraw from pain never trigger, as the brain never gets the message.

With this understanding of the Nav1.7 channels, one of the first research goals was to shut down the critical ion channels in normal people. From surgery to chronic pain treatment, there are many applications where suppressing the body’s natural pain response would be beneficial, including the goal of quieting pain without anesthesia’s tendency to completely numb a patient. However, no drug blocking the Nav1.7 channels completely blocked pain to the degree that congenital analgesia did, indicating that there were more than just missing ion channels at work.

Opioid options

Mice bred for congenital analgesia, revealing that in addition to missing ion channels in their nerves, the mutation also corresponded with an increase in opioid peptides. These peptides are a naturally occurring painkiller, so they made sense as the missing component to true painlessness. For people looking to avoid pain, this might lead to a combination treatment of ion channel blockers and lower doses of opioid drugs. Opioids, like morphine, can be very effective, but they’re not ideal for chronic pain as our bodies can build up tolerances for them, requiring larger doses to retain efficacy.

For the congenital analgesia patients who made this research possible, there may be hope for change as well. Naloxone is an established opioid blocker, and both mice and humans have been able to use it to enable their appreciation of pain. One participant, a 39-year-old woman, was given this treatment, then purposely burned with a laser on the finger. The novelty of saying “ouch!” for the first time was reported as positive, and she hopes that naloxone might be able to help children with congenital analgesia enjoy safer childhoods with the owies that the rest of us grew up with.

 

Source: Woman who has never felt pain experiences it for the first time by Jessica Hamzelou, New Scientist

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