Behavioral differentiation between itch and pain in mouse : PAIN (original) (raw)
Articles
Department of Anesthesiology, Yale University School of Medicine, P.O. Box 208051, 333 Cedar Street, New Haven, Connecticut 06520-8051, USA
*Corresponding author. Tel.: +1 203 785 6572; fax: +1 203 737 1528.
E-mail: [email protected]
Submitted April 11, 2008; revised July 30, 2008; accepted August 5, 2008.
Abstract
The standard rodent model of itch uses scratching with the hind limb as a behavioral response to pruritic stimuli applied to the nape of the neck. The assumption is that scratching is an indicator of the sensation of itch. But because only one type of site-directed behavior is available, one cannot be certain that scratching is not a response to nociceptive or other qualities of sensations in addition to, or instead of, itch. To extend the model, we administered chemical stimuli to the cheek of the mouse and counted scratching with the hind limb as an indicator of itch and wiping with the forelimb as an indicator of pain. An intradermal injection of histamine and capsaicin, known to evoke predominantly itch and pain, respectively, in humans, each elicited hind limb scratching behavior when injected into the nape of the neck of the mouse. In contrast, when the same chemicals were injected into the cheek of the mouse, there were two site-directed behaviors: histamine again elicited scratching with the hind limb, but capsaicin evoked wiping with the forelimb. We conclude that the “cheek model of itch” in the mouse provides a behavioral differentiation of chemicals that elicit predominantly itch in humans from those that evoke nociceptive sensations. That is, the model provides a behavioral differentiation between itch and pain in the mouse.
© 2008 Lippincott Williams & Wilkins, Inc.