title: Differentiating thermal allodynia and hyperalgesia using dynamic hot and cold plate in rodents.
abstract: In animal studies, thermal sensitivity is mostly evaluated on the basis of nociceptive reaction latencies in response to a given thermal aversive stimulus. However, these techniques may be inappropriate to differentiate allodynia from hyperalgesia or to provide information differentiating the activation of nociceptor subtypes. The recent development of dynamic hot and cold plates, allowing computer-controlled ramps of temperature, may be useful for such measures. In this study, we characterized their interest for studying thermal nociception in freely moving mice and rats. We showed that escape behavior (jumps) was the most appropriate parameter in C57Bl/6J mice, whereas nociceptive response was estimated by using the sum of paw lickings and withdrawals in Sprague-Dawley rats. We then demonstrated that this procedure allows the detection of both thermal allodynia and hyperalgesia after peripheral pain sensitization with capsaicin in mice and in rats. In a condition of carrageenan-induced paw inflammation, we observed the previously described thermal hyperalgesia, but we also revealed that rats exhibit a clear thermal allodynia to a cold or a hot stimulus. These results demonstrate the interest of the dynamic hot and cold plate to study thermal nociception, and more particularly to study both thermal allodynia and hyperalgesia within a single paradigm in awake and freely moving rodents.
  
  
  CONCLUSIONS
  Despite its clinical relevance, thermal allodynia is rarely studied by researchers working on animal models. As shown after stimulation of capsaicin-sensitive fibers or during inflammatory pain, the dynamic hot and cold plate validated in the present study provides a useful tool to distinguish between thermal allodynia and thermal hyperalgesia in rodents.
authors.affiliation: Nociception and Pain Department, Institut des Neurosciences Cellulaires et Intégratives, Centre National de la Recherche Scientifique, France.
authors.forename: Ipek
authors.initials: I
authors.lastname: Yalcin
authors.forename: Alexandre
authors.initials: A
authors.lastname: Charlet
authors.forename: Marie-José
authors.initials: MJ
authors.lastname: Freund-Mercier
authors.forename: Michel
authors.initials: M
authors.lastname: Barrot
authors.forename: Pierrick
authors.initials: P
authors.lastname: Poisbeau
mesh_terms: D000818:Animals; D001522:Behavior, Animal; D002211:Capsaicin; D002351:Carrageenan; D003080:Cold Temperature; D004121:Dimethyl Sulfoxide; D004924:Escape Reaction; D006614:Hindlimb; D006358:Hot Temperature; D006930:Hyperalgesia / Q000139:chemically induced / Q000175:diagnosis*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D010146:Pain / Q000139:chemically induced / Q000175:diagnosis*; D010147:Pain Measurement; D011597:Psychomotor Performance; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
chemical_list: D002351:Carrageenan; D002211:Capsaicin; D004121:Dimethyl Sulfoxide