Weight bearing evaluation in inflammatory, neuropathic and cancer chronic pain in freely moving rats.

Preclinical pain assessment remains a key step for the development of new and potent painkillers. Significant progress in pain evaluation has been achieved with the development of non-reflexive tools. Seeking efficient and clinically relevant devices for pain-related quality of life assessment, we evaluated a new Dynamic Weight Bearing (DWB) device based on pressure captors in three different preclinical chronic pain models. Inflammatory (CFA), neuropathic (CCI) and bone cancer pain (femoral tumor) models were evaluated in Sprague Dawley rats for mechanical allodynia using dynamic von Frey for pain-related behaviors and DWB for discomfort. We observed similar impairment patterns in all of the models for both von Frey (allodynia) and DWB (weight balance) during the complete observation period, starting at day 3 in CCI- and CFA-affected limbs and at day 14 in bone cancer-afflicted rats, indicating that the DWB could be a useful tool for supporting pain assessment. Interestingly, we demonstrated that the main compensation, when animals experienced pain, was seen in the forepaws, ranging from 46% to 69% of increased load compared to normal. Other pain-related coping behaviors were also measured, such as the time spent on each paw and the contact surface. Our results revealed that CFA, CCI and cancerous rats decreased the use of their ipsilateral hind paws by 30% and showed a 50% reduction in paw surface pressed against the floor. In conclusion, this new device improves methods for preclinical evaluation of discomfort and quality of life proxies and could be helpful in screening putative analgesics.