Fig. 5. Formalin-induced substance P (SP)-immunoreactivity expression variations are correlated with nociceptive behavioral responses. (A ) Bar heights give time-point-by-time-point formalin-induced variations of SP-immunoreactivity expression level in a day in wild-type mice. (B ) The circadian fluctuations in the variations of SP-immunoreactivity expression (blue circles , same data as shown in 5A) match the nociceptive behavioral circadian fluctuations in responses to formalin (red squares , same data as shown in fig. 4B) in wild-type. Pearson's correlation coefficient, r = 0.97, P < 0.01. ir = immunoreactivity; SP = substance P; ZT = zeitgeber time.