Role of peripheral and spinal 5-HT3 receptors in development and maintenance of formalin-induced long-term secondary allodynia and hyperalgesia

► Peripheral pre-treatment with 5-HT and m-CPBG increased formalin-induced pain. ► Spinal pre-treatment with m-CPBG increased formalin-induced pain. ► Peripheral and spinal ondansetron prevented formalin-induced pain. ► Ondansetron prevented the pronociceptive effect of m-CPBG at peripheral/spinal sites. ► Spinal post-treatment with ondansetron reversed established formalin-induced pain.