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The most predictive of the models for acute pain is the Formalin Test.  In this widely used model a 5% solution of formaldehyde is injected subcutaneously to mouse or rat paw to produce a biphasic pain response over a test period of 60 minutes.  The initial pain response occurs at 1 minute following subplantar injection of formalin and results from direct stimulation of nociceptors.  The second phase of pain response occurs after a period of sensitization (quiescent period) during which inflammatory phenomena take place (2). Opiod analgesics appear to be antinociceptive for both phases.  NSAIDS such as indomethacin appear to suppress only the second phase (3).

Pain response scoring includes counts per unit of time of reactions to the pain stimulus by licks, twitches, raising or shaking of the injected paw.

 

REFERENCES:    

1. Le Bars D, Gozariu M and Cadden SW (2001). Animal Models of Nociception. Pharmacol Rev 53: 597-652.
2. Dubisson D and Dennis SG (1977). The Formalin Test: A Quantitative Study of the Analgesic Effects of Morphine, Merperidine and Brain Stem Stimulation in Rats and Cats. Pain 4:161-174.
3. Jourdan D, Ardid D, Bardin L, Bardin M, Neuzeret D and Lanphouthacoul L (1997). A New Method of Pain Scoring in the Formalin Test in Rats. Pain 71:265-270.

 

Formalin-induced Pain Model
A valuable and widely used tool for investigating chronic pain
Species	Mouse or Rat
Group Size	6-10
Study Duration	One day
Readouts	Pain response Scoring

 

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