Gender-dependent effect on nociceptive response induced by chronic variable stress

It has previously been reported that exposure to repeated restraint stress induces hyperalgesia in male rats, an effect that was not observed in females. The aim of the present study was to investigate the effects of chronic variable stress over 40days on nociception threshold indexed by tail-flick latency in male and female adult rats. The results showed different behavior in chronically stressed animals when compared to the control group: male rats showed a decrease in tail-flick latency while females presented an increase in this parameter. For female rats this effect was independent of the phase of the estrous cycle. Several sources of data indicate that behavioral and physiological responses to stress are sexually dimorphic, including in nociception, and the estrous cycle appears to be a factor that influences opioid analgesia in female. These effects are modulated by the strain and conditions of nociception assay. Additional studies concerning the mechanisms involved in the hyperalgesic response in males and the differences on nociceptive response in females chronically exposed to stress are needed.