The effects of restraint stress on nociceptive responses induced by formalin injected in rat's TMJ.
It has been reported that stress can alter nociception from superficial tissues, such as skin and subcutaneous region. However, the influence of stress on an experimental deep nociception model is not understood. In this study, the temporomandibular joint (TMJ) formalin test was used to evaluate the effects of acute and chronic restraint stress on nociceptive responses in rats. Animals were initially submitted to one session of acute restraint stress (1 h) or exposed to chronic stress (40 days-1 h/day). Then, animals were killed immediately to collect blood for hormonal determinations by radioimmunoassay, or submitted to the TMJ formalin test to evaluate nociception. Rats submitted to acute restraint presented a performance similar to unstressed controls in the TMJ formalin test, whereas chronically stressed rats showed an increase in nociceptive responses. After 40 days of restraint, morphine was injected i.p. (1, 5 mg/kg or saline). The stressed rats displayed decreased morphine effects on nociception compared to unstressed controls. These findings suggest that repeated stress can produce hyperalgesia, which is, at least in part, due to alterations in the activity of opioid systems. This model may help elucidate the underlying neural mechanisms that mediate the effects of repeated stress on orofacial pain.
Gameiro
Gustavo Hauber
GH
Laboratory of Orofacial Pain, Department of Physiology, Faculty of Dentistry of Piracicaba, University of Campinas-Unicamp, Av. Limeira 901 C.P. 52, CEP 13414-900, Piracicaba, São Paulo, Brazil. ggameiro@fop.unicamp.br
Andrade
Annicele da Silva
Ada S
de Castro
Margaret
M
Pereira
Lígia Ferrinho
LF
Tambeli
Cláudia Herrera
CH
Veiga
Maria Cecília Ferraz de Arruda
MC
D000324:Adrenocorticotropic Hormone / Q000097:blood; D000701:Analgesics, Opioid / Q000494:pharmacology; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D003345:Corticosterone / Q000097:blood; D005557:Formaldehyde / Q000008:administration & dosage; D007267:Injections; D008297:Male; D009020:Morphine / Q000494:pharmacology; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D009619:Nociceptors / Q000187:drug effects*; D010147:Pain Measurement / Q000187:drug effects*; D051381:Rats; D017208:Rats, Wistar; D012149:Restraint, Physical; D013315:Stress, Psychological / Q000523:psychology*; D013704:Temporomandibular Joint
D000701:Analgesics, Opioid; D009292:Narcotic Antagonists; D005557:Formaldehyde; D009270:Naloxone; D009020:Morphine; D000324:Adrenocorticotropic Hormone; D003345:Corticosterone