The effects of restraint stress on nociceptive responses induced by formalin injected in rat's TMJ

Abstract

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.

Predictive behaviors for anxiety and depression in female Wistar rats subjected to cafeteria diet and stress

“…The animals were subjected to the stressor agent for an hour in the afternoon (from 2 p.m. to 3 p.m.), for five days a week, during 50 days. The selection of this model was based on several studies [28,[33][34][35]80,69,25,[56][57][58]. We associate it with the cafeteria diet as an attempt to simulate the daily life of the general population, at times when people undergo low intensity stresses.…”

Mechanical Allodynia and Thermal Hyperalgesia Induced by Experimental Squamous Cell Carcinoma of the Lower Gingiva in Rats

“…49 Under some experimental conditions, repeated or prolonged stress can elicit hyperalgesia. 16,40 We carefully monitored the mechanical and thermal sensitivity of the contralateral facial skin and hindpaw and did not see any significant changes during the experimental period. The hyperalgesia of the whisker-pad area may indeed represent a specific somatosensory change in this area rather than a generalized reaction to stress due to experimental condition.…”

Influence of early neonatal experience on nociceptive responses and analgesic effects in rats

“…18 Stressful stimuli such as maternal separation at an early age has been suggested to cause stress-induced analgesia. 10 Despite the observed differences, the data were not sufficiently robust to conclusively state that cross-fostering rats decreases sensitivity to thermal stimuli. Therefore, it seems that cross-fostering is not sufficiently stressful to cause major alterations in the rats' responses to thermal nociception in this case.…”