RAT FACIAL MECHANICAL ALLODYNIA BEHAVIOR (VON FREY FILAMENTS) METHOD

Animals

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 cutaneous sensitivity to a mechanical stimulation using von Frey filaments in rodents is considered a surrogate for tactile allodynia seen in patients and continues to be a standard in the preclinical pain field.

Rats are placed in Bowman restrainers (diameter 3.5”, length 10”) to acclimate to loose restraint for one hour on each of three days prior to testing. On test days, rats are placed in Bowman restrainers and a series of calibrated Semmes-Weinstein von Frey filaments (Stoelting, Wood Dale, IL, USA) with handle numbers 4.08, 4.31, 4.56, 4.74, and 4.93 are used to measure mechanical allodynia in rats. Filaments are applied perpendicularly to the periorbital region of the forehead above the eye with enough force to cause a slight buckling. Filaments are applied in ascending order beginning with the 4.08 handle number filament, and a positive response was defined as a recoil of the head, stroking of the face, vocalization, or aggressive behavior toward the filament. The filament force (g) that results in 2 positive responses out of 3 stimulations is defined as the facial sensitivity threshold. If no filament force produces 2 positive responses out of 3 stimulations, a maximum facial sensitivity threshold of 10 g is assigned.

This work was conducted by PsychoGenics Inc. (Paramus, NJ) in collaboration with PSPP, NINDS, NIH under contract # 75N95019D00026 and 75N95024D00038