Counterstimuli such as scratching, pinching, noxious heat and cold, and innocuous cooling and warming have been shown to inhibit itch in humans. In the present study, the effects of each of these counter-stimuli were determined on baseline firing rates and on sustained pruriceptive responses of rat trigeminothalamic tract neurons. We found that scratching had little, if any, effect on baseline firing levels but greatly reduced mean pruriceptive firing following scratching for nearly 1 min. None of the other noxious or innocuous counterstimuli significantly inhibited pruriceptive responses. Our results indicate that scratching, but not other counterstimuli, significantly reduces itch-induced responses of trigeminothalamic tract neurons.
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© 2016 the American Physiological Society.