title: The orofacial formalin test in rats: effects of different formalin concentrations.
abstract: In this study of the orofacial formalin test in rats, the effects of different formalin concentrations (0.2%, 0.5%, 1.5%, 2.5%, 5% and 10%) on the behavioural nociceptive response (face rubbing) was investigated. The histological responses of the skin were also evaluated. Increasing the concentration of formalin caused a parallel aggravation of histological signs of tissue inflammation and injury. All concentrations provoked an early phase of nociceptive response, but its intensity was not concentration-dependent. The 2nd phase of response to formalin only occurred for concentrations of 1.5% and higher. A positive relationship between the formalin concentration and the amplitude of the rubbing activity measured between 12 and 45 min after injection could be observed until 2.5% but with the highest concentrations (5 and 10%), the amplitude of the response decreased. Our findings indicate that the orofacial formalin test should be carried out using concentration between 0.5 and 2.5%. This is essential to assess increase as well as decrease in pain intensity. Moreover, this will have the effect of minimizing the suffering of the experimental animal.
authors.affiliation: Laboratoire de Physiologie Oro-Faciale, Faculté de Chirurgie Dentaire, Clermont-Ferrand 63000 France Département de Biologie, Faculté de Chirurgie Dentaire, Clermont-Ferrand 63000 France.
authors.forename: Pierre
authors.initials: P
authors.lastname: Clavelou
authors.forename: Radhouane
authors.initials: R
authors.lastname: Dallel
authors.forename: Thierry
authors.initials: T
authors.lastname: Orliaguet
authors.forename: Alain
authors.initials: A
authors.lastname: Woda
authors.forename: Patrick
authors.initials: P
authors.lastname: Raboisson
mesh_terms: D000818:Animals; D004305:Dose-Response Relationship, Drug; D005145:Face; D005557:Formaldehyde / Q000008:administration & dosage* / Q000494:pharmacology; D006225:Hand; D007267:Injections; D008046:Lip / Q000187:drug effects / Q000473:pathology; D008297:Male; D009043:Motor Activity / Q000187:drug effects*; D009055:Mouth; D009619:Nociceptors / Q000187:drug effects*; D009994:Osmolar Concentration; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D005557:Formaldehyde