• Andrew J Allchorne, Daniel C Broom, and Clifford J Woolf.
• Neural Plasticity Research Group, Department of Anesthesia & Critical Care, Massachusetts General Hospital & Harvard Medical School, 13th Street, Building 149 (#4309), Charlestown, MA 02129, USA. andrew.allchorne@gmail.com
• Mol Pain. 2005 Dec 14; 1: 3636.

BackgroundPain is elicited by cold, and a major feature of many neuropathic pain states is that normally innocuous cool stimuli begin to produce pain (cold allodynia). To expand our understanding of cold induced pain states we have studied cold pain behaviors over a range of temperatures in several animal models of chronic pain.ResultsWe demonstrate that a Peltier-cooled cold plate with +/- 1 degrees C sensitivity enables quantitative measurement of a detection withdrawal response to cold stimuli in unrestrained rats. In naïve rats the threshold for eliciting cold pain behavior is 5 degrees C. The withdrawal threshold for cold allodynia is 15 degrees C in both the spared nerve injury and spinal nerve ligation models of neuropathic pain. Cold hyperalgesia is present in the spared nerve injury model animals, manifesting as a reduced latency of withdrawal response threshold at temperatures that elicit cold pain in naïve rats. We also show that following the peripheral inflammation produced by intraplantar injection of complete Freund's adjuvant, a hypersensitivity to cold occurs.ConclusionThe peltier-cooled provides an effective means of assaying cold sensitivity in unrestrained rats. Behavioral testing of cold allodynia, hyperalgesia and pain will greatly facilitate the study of the neurobiological mechanisms involved in cold/cool sensations and enable measurement of the efficacy of pharmacological treatments to reduce these symptoms.

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