Nociceptive responses of WT and PK2-/- mice to noxious chemical stimuli. A. Nociceptive responses to capsaicin. Duration of licking in response to intraplantar injection of capsaicin (3 μg/10 μL) in WT (black bars, n = 8), PK2+/- (grey bars, n = 7) and PK2-/- mice (white bars, n = 8). B. Nociceptive responses to formalin. Time course of pain behavior induced by intraplantar injection of 5% formalin (20 μL) in WT (filled circles, n = 9) and PK2-/- mice (open triangles, n = 8). C. Formalin-induced pain behavior during the early and late phases. D. Visceral pain responses to acetic acid. Abdominal stretching produced by intraperitoneal injection of 0.6% acetic acid (5 μl/g body weight) was recorded. E. Visceral pain response to MgSO4. Abdominal stretching produced by intraperitoneal injection of 0.1 mM Mg SO4 (10 μl/g body weight) was recorded. All data are mean ± SEM. Asterisk, P < 0.05; two asterisks P < 0.01.