Abnormal mechanical and chemical pain response in <i>TrkAC-KI</i> mice.

<p>(A) Latency to mechanical stimulation using Von Frey apparatus was significantly lower in control mice one day after CFA injection, while <i>TrkAC-KI</i> mice did not show this response. Of note, the baseline latency to mechanical stimulation was lower in mutant mice (n = 9 for wild type and 13 for <i>TrkAC-KI</i>). (B) Lack of mechanical hypersensitivity after inflammation was also evident from a Dynamic Weight Bearing test. For <i>TrkAC-KI</i> mice, the weight distribution between inflamed and non-inflamed hindpaws was equal one day after CFA injection, while control mice favored the non-injected paw (n = 10 for wild type and 9 for <i>TrkAC-KI</i>). (C) Both <i>TrkAC-KI</i> and control mice developed thermal hyperalgesia one day after CFA injection (n = 8 for wild type and 6 for <i>TrkAC-KI</i>). The CFA effect (difference in latency between Day0 and day CFA+1) was significantly different between <i>TrkAC-KI</i> and wild type mice for Von Frey and DWB tests (A and B), but not for Hargreaves test (C). (D) <i>TrkAC-KI</i> mice exhibited severe deficit in pain from chemical injury when tested for nociceptive response after intraplantar injection of 10 µl of 2% formalin. Comparing to wild type littermates, <i>TrkAC-KI</i> mice had drastically reduced time of hindpaw shaking and biting during the first (0–10 min) and second (15–60 min) pain phases (n = 7 for each genotype). Data represent mean ± s.e.m * p<0.05, ** p<0.01.