Nociception- and anxiety-like behavior in rats submitted to different periods of restraint stress.
The aim of this study was to evaluate the effect of acute, sub-chronic and chronic stress on nociception induced by formalin injection in rats' temporomandibular joint (TMJ). It was evaluated the relation between blood levels of adrenocorticotropin, corticosterone, the levels of anxiety and nociceptive responses recorded after different stress protocols. Animals were initially submitted to acute restraint stress (15; 30 min and 1 h), or exposed to sub-chronic (3 days-1 h/day) or chronic stress (40 days-1 h/day). Then, animals were (1) killed immediately to collect blood for hormonal determinations; or (2) submitted to the elevated plus-maze to evaluate anxiety; or (3) submitted to the TMJ formalin test to evaluate nociception. It was also evaluated the role of serotoninergic and opioid systems in nociceptive changes induced by stress. For this, the serotonin-selective reuptake inhibitor (fluoxetine 10 mg/kg) and the opioid agonist (morphine 1-5 mg/kg) were administered before the nociception test. All stress protocols significantly raised the levels of ACTH or corticosterone, as well as the anxiety behavior. In relation to nociception, the chronic stressed animals showed an increase in nociceptive responses (hyperalgesia). In this group, there was a reduction in the morphine analgesic effects, suggesting dysfunction in the endogenous opioid system. Fluoxetine had an analgesic effect in both stressed and control groups, although this effect was more evident in the stressed group. It was concluded that stress-induced hyperalgesia may result from changes in the serotoninergic and opioid systems, which can explain, at least in part, the important link between stress and orofacial pain.
Department of Physiological Sciences, Faculty of Dentistry of Piracicaba, State University of Campinas-UNICAMP, Av. Limeira 901, C.P. 52, CEP 13414-900, Piracicaba, São Paulo, Brazil. ggameiro@fop.unicamp.br
Gustavo Hauber
GH
Gameiro
Paula Hauber
PH
Gameiro
Annicele da Silva
Ada S
Andrade
Lígia Ferrinho
LF
Pereira
Mariana Trevisani
MT
Arthuri
Fernanda Klein
FK
Marcondes
Maria Cecília Ferraz de Arruda
MC
Veiga
D000208:Acute Disease; D000324:Adrenocorticotropic Hormone / Q000097:blood*; D000701:Analgesics, Opioid / Q000494:pharmacology; D000818:Animals; D001007:Anxiety / Q000097:blood* / Q000209:etiology; D002908:Chronic Disease; D003348:Cortisone / Q000097:blood*; D004195:Disease Models, Animal; D004644:Emotions; D005106:Exploratory Behavior; D005473:Fluoxetine / Q000494:pharmacology; D008297:Male; D009020:Morphine / Q000494:pharmacology; D010146:Pain / Q000097:blood*; D017288:Pain Threshold / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D011957:Receptors, Opioid / Q000819:agonists; D012149:Restraint, Physical; D017367:Selective Serotonin Reuptake Inhibitors / Q000494:pharmacology; D013315:Stress, Psychological / Q000097:blood* / Q000150:complications / Q000523:psychology; D013997:Time Factors
D000324:Adrenocorticotropic Hormone; D000701:Analgesics, Opioid; D003348:Cortisone; D005473:Fluoxetine; D009020:Morphine; D011957:Receptors, Opioid; D017367:Selective Serotonin Reuptake Inhibitors