Sensory neurons and circuits mediating itch.

Chemicals that are used experimentally to evoke itch elicit activity in diverse subpopulations of cutaneous pruriceptive neurons, all of which also respond to painful stimuli. However, itch is distinct from pain: it evokes different behaviours, such as scratching, and originates from the skin or certain mucosae but not from muscle, joints or viscera. New insights regarding the neurons that mediate the sensation of itch have been gained from experiments in which gene expression has been manipulated in different types of pruriceptive neurons as well as from comparisons between psychophysical measurements of itch and the neuronal discharges and other properties of peripheral and central pruriceptive neurons.