Formalin-induced long-term secondary allodynia and hyperalgesia are maintained by descending facilitation

► Intra-RVM injection of lidocaine/YM022 reverses secondary allodynia or hyperalgesia. ► Formalin injection increases dynorphin in dorsal spinal cord sections at day 6. ► Intrathecal dynorphin antiserum reverses secondary allodynia and hyperalgesia. ► Secondary allodynia/hyperalgesia are maintained by descending mechanisms.