The formalin test refers to the quantification of characteristic nociceptive behaviors that occur in response to subcutaneous (s.c.) or intradermal injection of a dilute solution of formaldehyde in 0.9 % saline, typically into the dorsal or plantar hindpaw of rodents.
The formalin test was originally described by Dubuisson and Dennis (1977) using 50 μl of 5 % formalin injected s.c. into the dorsal surface of one forepaw in rats and cats. “Five percent formalin” consisted of 1 ml of saturated formaldehyde (37 %) in water + 19 ml 0.9 % saline (i.e., 1.85 % formaldehyde). It is now more common to inject between 0.2 % and 5 % formalin into the dorsal or plantar hindpaw, using 20–50 μl in rats or 10–25 μl in mice. Another common site is the lateral aspect of the muzzle, or the temporomandibular joint, in rats, as a model of orofacial pain (Clavelou et al. 1995). The hindpaw has replaced the forepaw...
- Coderre, T. J. (2001). Noxious stimulus-induced plasticity in spinal cord dorsal horn: Evidence and insights on mechanisms obtained using the formalin test. In M. M. Patterson & J. W. Grau (Eds.), Spinal cord plasticity: Alterations in reflex function (pp. 163–183). Boston: Kluwer Academic.Google Scholar
- McNamara, C. R., Mandel-Brehm, J., Bautista, D. M., Siemens, J., Deranian, K. L., Zhao, M., Hayward, N. J., Chong, J. A., Julius, D., Moran, M. M., & Fanger, C. M. (2007). TRPA1 mediates formalin-induced pain. Proceedings of National Academy of Sciences USA, 104, 13525–13530.Google Scholar
- Puig, S., & Sorkin, L. S. (1995). Formalin-evoked activity in identified primary afferent fibres: Systemic lidocaine suppresses phase-2 activity. Pain, 64, 345–355.Google Scholar
- Sawynok, J., & Liu, X. J. (2003). The formalin test: Characteristics and usefulness of the model. Reviews in Analgesia, 7, 145–163.Google Scholar