Several reports show greater prevalence of chronic pain conditions, as well as higher sensitivity to nociceptive stimuli, in women compared to men. However, around 80% of experimental studies are performed exclusively in male rodents (MogilJSetal.2005). The aim of this study was to characterize sex dimorphism in the development of cold and mechanical allodynia in Sprague-Dawley rats subjected to Spared Nerve Injury (SNI). Moreover, the development of anxiety- and depression-like behaviours were also studied as they are associated with long-lasting chronic pain.

Please see Figure 1 for a summary of the experimental design and methods.


SNI surgery induced cold allodynia in rats of both sexes. However, male-SNI rats developed cold allodynia later than females and showed a degree of recovery at the end of the experiment, an effect not observed in females. SNI-induced mechanical allodynia did not reach significance (vs Sham) until day 14 in females and day 42 in males.  In the OF, SNI did not induce any alteration in horizontal locomotor activity, but decreased vertical activity in males. There were no effects of SNI in the sucrose splash or sucrose preference tests in males or females.

Our results demonstrate differential development of SNI-induced nociceptive behaviour between male and female rats suggesting important sex-dimorphic modifications in pain pathways which persist at least 40 days after SNI surgery. Over this timeframe, SNI had no effect on depression- or anxiety- related behaviour in rats of either sex.

STUDY OF SEX DIFFERENCES IN PAIN-, DEPRESSION- AND ANXIETY-RELATED BEHAVIOURS IN THE RAT SPARED NERVE INJURY MODEL OF NEUROPATHIC PAIN