Reduced formalin-induced pain behaviour in hph mice. (a) and (b) time course after paw injection of 0.5 and 2.5% formalin. (c) and (d) total time licking and biting the paw during 0–10 min (phase 1) and 10–50 min (phase 2). A statistical significant reduction in spontaneous pain activity of hph mice was seen at both formalin-concentrations in the first phase compared to WT mice (0.5%: #p = 0.014, n = 9 and 2.5%: #p = 0.012, n = 9). Mann–Whitney t-test, two-tailed. No significant change in pain behaviour between genotypes was found in the second phase (0.5%: p = 0.48 and 2.5%: p = 0.69). Unpaired t-test, two-tailed. Data are presented as mean ± or + SEM.