Correlation of intact sensibility and neuropathic pain-related behaviors in eight inbred and outbred rat strains and selection lines

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Abstract
In some rat strains, total hindpaw denervation triggers autotomy, a behavior of self mutilation presumably related to neuropathic pain. Partial sciatic ligation (PSL) in rats produces tactile allodynia and heat hyperalgesia but not autotomy. Our aims in this study were to examine: (1) whether sensibility of intact rats to noxious and non-noxious stimuli is strain-dependent; (2) whether sensibility of intact rats could predict levels of autotomy, or of allodynia and hyperalgesia in the PSL model; and (3) whether autotomy levels are correlated with levels of allodynia or hyperalgesia. Here we report that in two inbred rat strains (Lewis and Fisher 344), two outbred rat strains (Sabra and Sprague-Dawley) and four selection lines of rats (Genetically Epilepsy-Prone Rats, High Autotomy, Low Autotomy and Flinders Sensitive Line), tactile sensitivity and response duration to noxious heat of intact animals were strain-dependent. Levels of autotomy following hindpaw denervation and of allodynia and hyperalgesia in the PSL model were also strain-dependent. Thus, these traits are determined in part by genetic factors. Sensory sensibility of intact rats was not correlated with levels of autotomy following total denervation, or allodynia and hyperalgesia following partial denervation. We suggest that preoperative sensibility of intact rats is not a predictor of levels of neuropathic disorders following nerve injury. Likewise, no correlation was found between autotomy, allodynia and hyperalgesia, suggesting that neuropathic pain behaviors triggered by nerve injury of different etiologies are mediated by differing mechanisms.