A particular set of brain neurons may be behind registering itch and inducing us to scratch.
Everyone knows what it’s like to itch. And the sensation can drive you mad. Or, if you’re Yan-Gang Sun of the Chinese Academy of Sciences, it can drive you to explore how the brain tells you it’s time to scratch: “Our study is aiming to understand the brain mechanism that promotes the itch-scratching cycle.”
Itching can be caused by a number of irritants, from allergic reactions and abrasive textures to bug bites, skin conditions, infections or drugs. The usual solution is to simply scratch. But this cycle of itching and scratching, if it continues unabated, can actually damage tissue—like if you scratch yourself raw.
And Sun notes that: “Effective treatment for chronic itch is still lacking. This is largely due to our limited knowledge about the neuromechanism of itch.”
Over the past 10 years, scientists have learned a lot about how the itch signal is carried from the skin to the spinal cord.
“In contrast, we know very little about how the itch information is processed in the brain, and how the brain can dynamically modulate the processing of itch.”
Sun and his colleagues focused their attention on the periaqueductal gray…a brain region known to be involved in handling the closely related sensation of pain. They started by exposing mice to histamine or the antimalarial drug chloroquine, both of which trigger scratching.
And they found that this itch-inducing treatment activates a particular set of neurons within the periaqueductal gray: neurons that produce a neurochemical called Tac1.
When the researchers then eliminated this set of neurons, scratching was significantly diminished. And when they activated the neurons—even in the absence of a chemical irritant—the scratching resumed. Sun thus thinks of these Tac1-expressing neurons as the itch neurons in the brain. Getting these neurons firing makes animals itchy and gets them to scratch. His findings appear in the journal Neuron. [Zheng-Run Gao et al., Tac1-Expressing Neurons in the Periaqueductal Gray Facilitate the Itch-Scratching Cycle via Descending Regulation]
“These itch neurons in the brain can be a potential central therapeutic target for breaking the vicious itch-scratching cycle associated with chronic itch.”
Which could be a big relief for many irritated people.
[The above text is a transcript of this podcast.]