Assessment of an Electronic Mechanical Sensory Threshold Testing Device (RatMet) in Wistar rats (Rattus norvegicus)

von Frey (vF) monofilaments are used to quantify mechanical hypersensitivity and nociception in rodents; however, this method of testing has been criticized due to inconsistencies in testing methods, filament properties, and nonlinearity. This study compared withdrawal thresholds measured by using vF monofilaments with those of a novel mechanical threshold testing device currently in development (RatMet) in a carrageenan inflammatory model in 9- to 11-wk-old male Wistar rats. Rats were randomly assigned to assessment of mechanical hypersensitivity after intraplantar carrageenan injection by using either vF monofilaments (n = 10) or the RatMet device equipped with 3 sizes of probe tips (0.9 mm [RM0.9], n = 15; 0.5 mm [RM0.5], n = 11; and 0.09 mm [RM0.09], n = 11). All RatMet probe sizes and vF monofilaments identified a reduction in withdrawal threshold after treatment. Systematic differences in threshold were identified between vF and both RM0.9 and RM0.5 groups; RM0.09 did not differ from vF. Withdrawal thresholds showed linear relationships with probe diameter, square root of probe diameter, and area of the RatMet probes. In contrast, exponential relationships were observed with the vF monofilaments. Furthermore, none of the RatMet probe results differed in accuracy when comparing a single test with the averages of 3 or 5 tests per time point. Overall, the RatMet device measurements have construct validity even when the number of testing replicates is low. These data indicate that the RatMet device produces data comparable with those from vF monofilaments, with the potential for a shortened testing period without a decrease in accuracy.