Gate control of mechanical itch by a subpopulation of spinal cord interneurons

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Science  30 Oct 2015:
Vol. 350, Issue 6260, pp. 550-554
DOI: 10.1126/science.aac8653

A circuit controlling mechanical itch

Considerable progress has been made in understanding and treating chemically induced itch. However, little is known about the mechanisms underlying mechanically evoked itch. Bourane et al. produced a model of mechanical itch by reducing the number of neuropeptide Y–expressing inhibitory spinal interneurons. This led to a selective increase in mechanically evoked itch-like behavior in mice. In contrast, chemically evoked itch or pain behavior remained unaffected.

Science, this issue p. 550


Light mechanical stimulation of hairy skin can induce a form of itch known as mechanical itch. This itch sensation is normally suppressed by inputs from mechanoreceptors; however, in many forms of chronic itch, including alloknesis, this gating mechanism is lost. Here we demonstrate that a population of spinal inhibitory interneurons that are defined by the expression of neuropeptide Y::Cre (NPY::Cre) act to gate mechanical itch. Mice in which dorsal NPY::Cre-derived neurons are selectively ablated or silenced develop mechanical itch without an increase in sensitivity to chemical itch or pain. This chronic itch state is histamine-independent and is transmitted independently of neurons that express the gastrin-releasing peptide receptor. Thus, our studies reveal a dedicated spinal cord inhibitory pathway that gates the transmission of mechanical itch.

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