Von Frey testing

Rats were allowed to acclimate to testing room, chambers, and light conditions for 2 h a day for 3 days prior to facial testing. Rats were handled for a single 5-min session at 24-h prior to habituation to the behavior chambers. Only rats that met a baseline of 8 g facial withdrawal threshold and 15 g hindpaw withdrawal threshold were included in the study. Following establishment of baseline, animals were given their respective injections. Facial withdrawal thresholds were determined by applying von Frey filaments to the periorbital region of the face (the midline of the forehead at the level of the eyes) in an ascending/descending manner starting from the 1 g filament. Briefly, if an animal did not respond, increasing filament forces were applied until the 8 g filament was reached or until a response was observed. If the animal responded to a specific filament, decreasing filament forces were applied until the 0.4 g filament was reached or until there were no responses observed. If no responses are observed, i.e. facial baseline is reached, the filaments tested are 1 g, 2 g, 4 g, 6 g, 8 g. Hindpaw withdrawal thresholds were determined via the same paradigm with a maximum of beginning with the 2 g filament and with a maximum of 15 g and a minimum of 0.6 g if an animal reaches a baseline withdrawal threshold on the paw the filaments tested are 2 g, 4 g, 6 g, 8 g, 15 g. Following central administration of IL-6 both the left and right hindpaws were tested; the paw showing greater hypersensitivity was then tested to be included in the data set.