Establishing a new model of cancer neuropathic pain in rats

To guide the treatment of malignant neuropathic pain (MNP) in clinical practice, by inoculating MADB-106 breast cancer cells into the right L4 nerve root in Sprague-Dawley rats, a rat model of MNP was established, providing basic conditions for the study of neuropathic pain and development and application of therapeutic drugs. As the tumor grew over time, it pressed the nerve roots, causing nerve damage. The spinal nerve ligation (SNL) model, which is a neuropathic pain model widely used in rats, was compared with the L4 nerve root SNL model, and histologic examination of the nerve tissue of both models was performed by electron microscopy. In addition to the infiltration and erosion of the L4 nerve by tumor cells, the tumor tissue gradually grew and compressed the L4 nerve roots, resulting in hyperalgesia of the rat's posterior foot on the operative side. Some spontaneous pain phenomena were also observed, such as constant lifting or licking of the posterior foot on the operative side under quiet conditions. Electron microscopy images showed that nerve injury was due to progressive compression by the tumor, cells of which were visualized, but the injury was lighter than that in SNL rats. Imaging showed a paravertebral tumor near the L4 nerve root in the carcinomatous neuropathic pain model rat. These results suggest that progressive compression of the nerve by a malignant tumor leads to nerve damage similar to the behavioral changes associated with chronic compression injury resulting from a loose ligature of the nerve. The cancer neuropathologic pain model at the L4 nerve root was successfully established in Sprague-Dawley rats.