New Solution: MouseMet and RatMet: refined mechanical and thermal nociceptive testing

Fundamental and pharmacological studies in pain require nociceptive threshold testing (NTT) to detect increases or decreases in sensitivity to a noxious stimulus. Thermal and mechanical sensitivity testing is very widely used in such research, and rodents, primarily mice, are the most common species studied. Testing with von Frey filaments and hot plate technology, principally the Hargreaves system, are currently the accepted methods for mechanical and heat testing respectively. However, these have a number of scientific and animal welfare limitations.

In response to the need for better systems Topcat developed MouseMet RatMet, novel rotary force transducers with a range specific for mice (0.1-7gf) and rats (1-80gf). This provides a single ramped mechanical stimulus that replaces the succession of “go/no go” tests and post-testing calculations required by filaments. The rotary action transducer is used with species-specific cages designed to make access to the foot and controlled application of the stimulus more efficient; minimising the time taken to obtain results and the time each animal has to spend away from the home cage environment. Threshold force is automatically recorded and the force ramp displayed. A thermal stimulus has also been developed to work with the same transducer and is applied to the plantar surface of the foot in the same way as the mechanical test, with the animal still in the same cage

A height adjustable system of one-dimensional cages was developed to ensure that the subject, after first exploring the environment, will sit sideways to the tester. Carefully spaced foot bars ensure that the animal can sit naturally throughout the procedure, while ensuring optimal access to the appropriate test site on the foot. This enhances animal well-being compared with traditional square and mesh-floored cages as testing is quicker and easier.

Both systems can be used in all circumstances where NTT is used and provide significant improvements over the current methodologies used for mechanical and thermal stimuli. Replacing traditional methods with these systems would make a significant contribution to refinement and reduction where there is no alternative to in vivo studies. A single ramped stimulus replaces the series of stimuli (usually at least five) required for testing with filaments. Combined with one-dimensional cages, this offers a quicker and less stressful approach, as the animal has to be handled less. Mechanical/thermal NTT data obtained these systems are less variable and less prone to errors than current approaches. These characteristics may permit smaller animal group sizes of five or six animals.

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