Neurological Disorders: Nociception Formalin Paw Assay
The formalin paw assay has been recognized for a number of years as an assay for hyperalgesia, as well as initial acute nociception. Recently, this assay has been automated and thus has become available for use in high throughput analysis. Two wild type (one male and one female) and six homozygous mice (three males and three females) from each project are tested for nociception with Automatic Nociception Analyzers (purchased from the Ozaki lab at University of California, San Diego). A metal band is placed around the left hind paw of each mouse with superglue 30 minutes prior to testing. After the 30-minute acclimation period, 20 μl of 5% formalin is subcutaneously injected in the dorsal surface of the left hind paw. Mice are individually housed in cylindrical chambers for 45 minutes. A computer records flinches per minute, total flinches for phase I (acute phase = first 8 minutes), and total flinches for phase II (tonic phase between 20 - 40 minutes) through an electromagnetic field. Pharmacological validation of this assay has been performed using morphine (decreased paw flinching) and MK-801, an NMDA receptor blocker (increased paw flinching; Yaksh et al., 2001).
Displayed below is a sample graph of how paw flinching observations are presented. In comprehensive phenotypic data packages graphs are interactive. Raw or calculated data and statistics can be seen by clicking on points in the graph.
Figure illustrates median paw flinches of mutant mice following formalin injection. Total flinches for wild type littermates (green circle), homozygous (red diamond), and recent historical wild type (purple line) mice are plotted against long-term historical median paw flinches (+/- 2 standard deviations) for wild type animals (green shading). Recent wild type values are calculated from data collected within 60 days of current measures and long-term historical values were derived from data collected on more than 10,000 wild type mice.
Yaksh T, Ozaki G, McCumber D, Rathbun M, Svensson C, Malkmus S, Yaksh M. (2001) An automated flinch detecting system for use in the formalin nociceptive bioassay, Journal of Applied Physiology, 90:2386-2402.