They found that although a certain set of spinal neurons with gastrin-releasing peptide receptors (GRPR) were crucial for itch-signal processing, those neurons did not send the itch signal directly to the brain.
Instead, GRPR neurons sent the signal through an intermediary patch of neurons in the spine, which act as a pathway into a brainstem region known as the parabrachial nucleus, or PBN. The PBN then serves as the first central relay point for itch signal information entering the brain, according to the study.
"Our study revealed a long-range neural circuit that is critical for transmitting itch signal from the spinal cord to brain," Dr. Sun Yangang of the Chinese Academy of Sciences' Institute of Neuroscience, who led the study, told China’s Xinhua news agency.
The intermediary pathway between the GRPR neurons and the brain could itself be manipulated to block the itch signal, researchers found.
In their study, published last week in the journal Science, the scientists were able to suppress itching and scratching in mice by inhibiting those intermediary pathway neurons through optogenetics — a technique that uses light to stimulate or suppress the activity of neurons in living tissue.
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Mice were bred with genetically modified neurons that react to light, giving researchers the power to activate or deactivate the spinal pathway involved in relaying information about itchiness.
In other words, the researchers found they could turn off the sensation of itchiness by disabling the mid-stage neurons that were transmitting itch signals to the brain, effectively blocking the link between the GRPR neurons and the PBN in the brainstem.
That finding points to the potential for new forms of long-term therapy, providing effective ways can be found to interrupt the analogous itch-signal pathway in humans.
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