Studies are conducted in adult male and female Sprague Dawley rats (Envigo) in an AAALAC-accredited facility with approval from an Institutional Animal Care and Use Committee, and implemented in accordance with the Guide for the Care and Use of Laboratory Animals 8th Edition (National Research Council, 2011) with standards set by the National Institutes of Health.

Experimental procedure

Evaluation of hind paw guarding behavior in rat pain models has been used to investigate the efficacy of analgesic compounds. This non-evoked behavior is displayed when the animal reduces the weight placed on a painful limb (Brennan et al., 1996).

Guarding behavior is measured in rats thoroughly acclimated to individual chambers placed on a wire mesh floor. Guarding score is measured every 5 minutes for 60 minutes (13 times) by observing the painful hind paw through the mesh floor of the chambers. Guarding is scored on a scale from 0 to 3 as follows:

  1. the injured paw is flat on the mesh and the rat is putting weight on it (paw is directly under the body). The plantar surface, toes, and heel of the paw must be on the mesh floor firmly, balancing weight uniformly with the contralateral paw.
  2. the injured heel is raised, but the animal is still bearing some weight on the plantar surface and toes. The distribution of weight between the ipsilateral and contralateral paws ceases to be equal, and no signs of blanching, or whitening, of the ipsilateral paw appear.
  3. the injured paw is not bearing weight and only touches the mesh floor by the toes. Heel and possibly plantar surface and base of the toes are raised up, but not completely away from the mesh floor, with an unbalanced support of weight. To check that the ipsilateral foot is not supporting the body weight, the experimenter can use a blunt pen or instrument and gently try to lift first the uninjured paw, then the injured paw while avoiding the injury site. If the ipsilateral foot is easily lifted with limited resistance, a score of 2 is given.
  4. the entire injured paw is completely off the mesh floor surface and held close to the body.

The scores for each animal are added and a final score of the sum calculated from the 13 scores recorded (maximum score of 39).


Brennan TJ, Vandermeulen EP, Gebhart GF (1996). Characterization of a rat model of incisional pain. Pain 64: 493-501. PMID: 8783314 DOI: 10.1016/0304-3959(95)01441-1

National Research Council (2011). Guide for the Care and Use of Laboratory Animals: Eighth Edition. Washington, DC: The National Academies Press

This work was conducted by PsychoGenics Inc. (Paramus, NJ) in collaboration with PSPP, NINDS, NIH under contract # 75N95019D00026