When an animal suffers an injury or inflammation, nearby tissue usually becomes highly sensitive to pain. Skin becomes red and puffy, for example, and is hypersensitive to heat. This condition, called «thermal hyperalgesia," acts as a warning that helps animals avoid further injuries.
The only known animals unable to feel thermal hyperalgesia are naked
A connection between nerve growth and thermal sensitivity
Hyperalgesia is mediated by the signaling molecule Nerve Growth Factor (NGF), which is also responsible for the growth of new nerves, especially during embryonic development. Hyperalgesia occurs when inflamed or injured tissue releases NGF molecules which subsequently bind to protein molecules on the surfaces of specialized,
A small change in the TrkA receptor has a big effect
TrkA receptors evolved in an ancient animal and have been passed down to all its descendants. TrkA is so important that it has been protected from most evolutionary change.
When the researchers compared the receptor of naked
In naked
An evolutionary sweet spot?
NGF has another important function: it stimulates the growth and maintenance of nerves as the nervous system develops in the embryo. That’s why defects of the TrkA receptor in other mammals often lead to a degeneration of the nervous system during embryonic development. «The nervous system of the naked
The difference surely makes life more bearable for the rodents, which live underground in densely packed colonies. Injuries and inflammations are common, and under the same conditions other mammals would suffer intense, continual pain.
That’s a daily experience for many people who suffer from chronic pain. In many cases the problem also involves NGF and TrkA; treatments that block the binding of these two molecules have had very positive effects in clinical trials. It’s another example, Gary says, of how basic research — even when it starts in a very unusual animal — could pave the way toward new human therapies.
