How are nociceptors altered by tissue injury?
When there is tissue injury (e.g., an arthritic joint), the nociceptor is exposed to an inflammatory “soup” containing a host of molecules that influence the properties of the nociceptor. These molecules include prostaglandin products of arachidonic acid metabolism, bradykinin, cytokines, serotonin, and growth factors (notably nerve growth factor). This all occurs in the setting of lowered pH. Together these molecules contribute to peripheral sensitization, a process through which the threshold for firing of the nociceptor is lowered. The most direct way to treat peripheral sensitization is with nonsteroidal anti-inflammatory drugs, (NSAIDS), which block the cyclooxygenase enzyme. In clinical development are antibodies that target NGF for the management of osteoarthritis pain.