Behavioral assessment of neuropathic pain in preclinical models

One of the greatest challenges to creating more efficacious medications for pain control has been the heterogeneity of the “chronic pain condition.” It is now appreciated that distinct mechanisms contribute to physiological pain, to pain arising from tissue damage, and to pain arising from injury to the nervous system. Unlike nociceptive pain, neuropathic pain can persist long after the initiating event has healed and is the expression of an abnormal processing of sensory information by the nervous system. Neuropathic pain is very heterogeneous and can originate from nerve injury associated with a wide array of conditions such as direct trauma to nerves, inflammation/nerve compression, metabolic diseases, infections, tumors, toxins, and primary neurological diseases. To study pain transmission, identify new pain targets, and characterize the potential analgesic profile of novel compounds for neuropathic pain relief, an array of experimental animal pain models has been developed mainly in rodents, trying to reflect as many “neuropathic pain conditions” as possible. However, one should remember that even for patients labeled under the same “neuropathic pain disease,” the pain experience is unique and can be very different from one patient to the other, increasing the difficulties of modeling such painful states in animal models. The present review will describe the most utilized animal models of neuropathic pain and the various methods used to assess degrees of hyperalgesia and allodynia in these animals, outlining similarities and differences observed under various preclinical “neuropathic pain conditions.” Drug Dev. Res. 67:302–307, 2006. © 2006 Wiley‐Liss, Inc.