Wire mesh floor

Nociceptive thresholds were measured using calibrated von Frey filaments (4–26 g; North Coast Medical, Morgan Hill, CA). Rats (n = 6 per group) were placed in elevated plastic chambers with a wire mesh floor (IITC Life Science Inc., Woodland Hills, CA) and allowed to habituate prior to testing. Filaments were applied perpendicularly to the medial plantar surface of the hind paw from below the mesh floor in an ascending order of filament force, beginning with the lowest filament. Filaments were applied until buckling occurred for approximately 2 s. Mechanical paw withdrawal thresholds (PWTs) correspond to the lowest force that elicited a withdrawal of the hind paw in at least two out of three applications. Forces larger than 26 g would physically elevate the paw and did not reflect pain-like behavior. For time course procedures, rats received a single injection of a drug or vehicle immediately following the t=0 measurement, and were assessed every 30 minutes. In experiments where a cumulative dosing procedure was used, measurements were recorded every 30 minutes, and immediately after each measurement, rats received the next dose of drug.

Mechanical hypersensitivity was measured using Von Frey filaments consisting of calibrated filaments (10–60 g; North Coast Medical, Morgan Hill, CA). Rats were placed in elevated plastic chambers with a wire mesh floor (IITC Life Science Inc., Woodland Hills, CA) and allowed to habituate prior to testing. Filaments were applied perpendicularly to the medial plantar surface of the same hind paw (right) from below the mesh floor in an ascending order of filament force, beginning with the lowest filament (10 g). A filament was applied until buckling occurred and maintained for approximately 2 s. Mechanical thresholds correspond to the lowest force that elicited a behavioural response (withdrawal of the hind paw) in at least two out of three applications.