Inflammatory Assays for Neuropathic Pain

Inflammatory assays were used in this study since the limited duration of facial grimacing is not appropriate for neuropathic assays. Complete Freund's adjuvant (CFA), kaolin and carrageenan were all obtained from Sigma (St. Louis, MO). In the intraplantar CFA model [11 ], rats were injected with 50% CFA, in a 150 μl injection volume, into the plantar surface of one hind paw. Rats (n = 10) were tested before, and 1 h, 4 h, 6 h, 24 h and (in a separate cohort; n = 8) 48 h and 7 days post-injection. In the rat intraarticular kaolin/carrageenan model [12 (link)], 2% kaolin and 2% carrageenan were successively injected (separated by 10 min), under isoflurane/oxygen anesthesia, into one knee joint, each in a volume of 200 μl. Rats (n = 6) were tested before, and 3 h, 6 h, and 12 h post-injection. Group sizes were based on our experience using similar assays in mice [9 (link)].