title: The effects of acute restraint stress on nociceptive responses evoked by the injection of formalin into the temporomandibular joint of female rats.
abstract: The temporomandibular joint (TMJ) formalin test was used to evaluate the effects of acute restraint stress on the nociceptive behavioral responses of female rats during proestrus and estrus phases of the estrous cycle. Rats were subjected to one session of restraint stress (15, 30 min or 1 h). They were then either immediately killed to allow the collection of blood for hormonal radioimmunoassay determinations or subjected to TMJ formalin test to evaluate nociception. All stress protocols significantly raised the plasma concentrations of corticosterone. The performance of rats subjected to 15 and 30 min of restraint stress was similar to that of control rats, whereas rats that were stressed for 1 h showed a decrease in nociceptive responses, during both proestrus and estrus phases. The stress-induced analgesia (SIA) was greater in the proestrus phase. To evaluate the role of kappa-opioid receptors, the selective receptor kappa-opioid antagonist nor-binaltorphimine (nor-BNI; 200 microg or saline) was injected into the TMJ 24 h prior to the 1 h stress period and the TMJ formalin test. The local administration of nor-BNI partially reversed the SIA during the proestrus phase. These findings suggest that (1) acute stress for 1 h can produce analgesia both during proestrus and estrus phases; this effect is greater during the proestrus phase and (2) kappa-opioid receptor activation is involved in the SIA observed in the proestrus phase.
authors.affiliation: Laboratory of Orofacial Pain, Department of Physiological Sciences, Piracicaba Dental School, University of Campinas-UNICAMP, Piracicaba, Sao Paulo, Brazil.
authors.forename: Ana Paula
authors.initials: AP
authors.lastname: Botelho
authors.forename: Gustavo Hauber
authors.initials: GH
authors.lastname: Gameiro
authors.forename: Carlos Eduardo da Silva Nossa
authors.initials: CE
authors.lastname: Tuma
authors.forename: Fernanda Klein
authors.initials: FK
authors.lastname: Marcondes
authors.forename: Maria Cecília Ferraz
authors.initials: MC
authors.lastname: de Arruda Veiga
mesh_terms: D000208:Acute Disease; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects / Q000502:physiology; D004971:Estrus / Q000502:physiology; D005260:Female; D005557:Formaldehyde / Q000494:pharmacology; D009271:Naltrexone / Q000031:analogs & derivatives / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D009619:Nociceptors / Q000187:drug effects / Q000502:physiology*; D010146:Pain / Q000139:chemically induced / Q000503:physiopathology*; D010147:Pain Measurement; D011359:Proestrus / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D011957:Receptors, Opioid / Q000502:physiology; D012149:Restraint, Physical; D013312:Stress, Physiological / Q000502:physiology*; D013704:Temporomandibular Joint / Q000187:drug effects / Q000502:physiology; D013705:Temporomandibular Joint Disorders / Q000139:chemically induced / Q000503:physiopathology*
chemical_list: D009292:Narcotic Antagonists; D011957:Receptors, Opioid; D005557:Formaldehyde; C051844:norbinaltorphimine; D009271:Naltrexone