A central neural circuit for itch sensation

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Science  18 Aug 2017:
Vol. 357, Issue 6352, pp. 695-699
DOI: 10.1126/science.aaf4918

The circuits of itching and scratching

Itch is a major clinical problem with poor treatment options. In the past few years, much progress has been made in identifying itch-selective molecules and neurons. However, we know very little about the brain circuits underlying itch processing. Mu et al. found that a subpopulation of itch-processing neurons in the spinal cord directly excite other neurons that project to a brain stem structure called the parabrachial nucleus. Inhibition of this spino-parabrachial pathway reduced itching and scratching in mice.

Science, this issue p. 695


Although itch sensation is an important protective mechanism for animals, chronic itch remains a challenging clinical problem. Itch processing has been studied extensively at the spinal level. However, how itch information is transmitted to the brain and what central circuits underlie the itch-induced scratching behavior remain largely unknown. We found that the spinoparabrachial pathway was activated during itch processing and that optogenetic suppression of this pathway impaired itch-induced scratching behaviors. Itch-mediating spinal neurons, which express the gastrin-releasing peptide receptor, are disynaptically connected to the parabrachial nucleus via glutamatergic spinal projection neurons. Blockade of synaptic output of glutamatergic neurons in the parabrachial nucleus suppressed pruritogen-induced scratching behavior. Thus, our studies reveal a central neural circuit that is critical for itch signal processing.

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