Figure 3.

Responses to noxious heat was determined in the (A) tail flick and (B) hotplate tests. tail flick latency (mean ± SEM) were similar between the two genotypes at high- and low-light beam-intensities. After swim stress, analgesia was observed as a significant delay in tail flick latency, which also did not differ between the genotypes. In contrast, pain-response latency in the hotplate test was highly significantly increased in mice with the Tac1^−/− genotype. Responses to noxious chemical stimuli were determined in the (C) acetic acid-induced abdominal constriction assay and in the (D) formalin test. No significant difference between the genotypes was found in the number of abdominal constriction, but Tac1^−/− mice did not show any significant pain responses in the early or late phase of the formalin test. Data were analyzed with the Mann–Whitney U test, except the stress-induced analgesia was analyzed with the Wilcoxon signed rank test. ∗, P < 0.05; ∗∗∗, P < 0.0005. The number at the bottom of each bar indicates the number of animals analyzed.