Reduced nerve injury-induced neuropathic pain in kinin B1 receptor knock-out mice

Abstract

Injury to peripheral nerves often results in a persistent neuropathic pain condition that is characterized by spontaneous pain, allodynia, and hyperalgesia. Nerve injury is accompanied by a local inflammatory reaction in which nerve-associated and immune cells release several pronociceptive mediators. Kinin B1 receptors are rarely expressed in nontraumatized tissues, but they can be expressed after tissue injury. Because B1 receptors mediate chronic inflammatory painful processes, we studied their participation in neuropathic pain using receptor gene-deleted mice. In the absence of neuropathy, we found no difference in the paw-withdrawal responses to thermal or mechanical stimulation between B1 receptor knock-out mice and 129/J wild-type mice. Partial ligation of the sciatic nerve in the wild-type mouse produced a profound and long-lasting decrease in thermal and mechanical thresholds in the paw ipsilateral to nerve lesion. Threshold changed neither in the sham-operated animals nor in the paw contralateral to lesion. Ablation of the gene for the B1 receptor resulted in a significant reduction in early stages of mechanical allodynia and thermal hyperalgesia. Furthermore, systemic treatment with the B1 selective receptor antagonist des-Arg9-[Leu8]-bradykinin reduced the established mechanical allodynia observed 7-28 d after nerve lesion in wild-type mice. Partial sciatic nerve ligation induced an upregulation in B1 receptor mRNA in ipsilateral paw, sciatic nerve, and spinal cord of wild-type mice. Together, kinin B1 receptor activation seems to be essential to neuropathic pain development, suggesting that an oral-selective B1 receptor antagonist might have therapeutic potential in the management of chronic pain.

Figure 1.

Time-dependent thermal hyperalgesia in the ipsilateral paw (A) but not in contralateral paw (B) induced by partial sciatic nerve lesion (PSNL) in wild-type (+/+) or B₁ receptor knock-out (-/-) mice. Data represent the latencies of the response to thermal stimuli. Each point represents the mean ± SEM of four to six mice. In some cases, the error bars are hidden within the symbols. ^*p < 0.05 or ^**p < 0.01 denotes the significance level when compared with the wild-type sham-operated group. ^#p < 0.05 or ^##p < 0.01 denotes the significance level when compared with the wild-type PSNL group (one-way ANOVA followed by Student-Newman-Keuls test).

Figure 2.

A, Mechanical sensitivity to von Frey hairs stimulation in wild-type (+/+) or B₁ receptor knock-out (KO) (-/-) mice before nerve injury. B, Increased mechanical sensitivity in the ipsilateral paw observed 7 d after partial sciatic nerve lesion (PSNL) in wild-type mice (+/+) but not in B₁ receptor knock-out mice (-/-). Data represent the response frequency to mechanical stimuli. Each point represents the mean ± SEM of four to six mice. In some cases, the error bars are hidden within the symbols. ^*p < 0.05 or ^**p < 0.01 denotes the significance level when compared with the wild-type sham-operated group. ^#p < 0.05 or ^##p < 0.01 denotes the significance level when compared with the wild-type PSNL group (one-way ANOVA followed by Student-Newman-Keuls test).

Figure 3.

Time-dependent mechanical allodynia in ipsilateral paw (A) but not in contralateralpaw (B) induced by partial sciatic nerve lesion in wild-type (+/+) or B₁ receptor knock-out (-/-) mice. Data represent the frequency response to 0.16 g von Frey hair stimulation. Each point represents the mean ± SEM of four to six mice. In some cases, the error bars are hidden within the symbols. ^*p < 0.05 or ^**p < 0.01 denotes the significance level when compared with the wild-type sham-operated group. ^#p < 0.05 or ^##p < 0.01 denotes the significance level when compared with the wild-type partial sciatic nerve lesion group (one-way ANOVA followed by Student-Newman-Keuls test).

Figure 4.

Antinociception produced by treatment with the selective B₁ receptor antagonist des-Arg⁹-[Leu⁸]-bradykinin (DALBK; 150 nmol/kg) in mechanical allodynia in the ipsilateral paw observed after partial sciatic nerve lesion in wild-type mice. A, Time course of the antiallodynic effect 7 d after surgery. B, Anti-allodynic effect of DALBK 7-42 d after nerve injury when administered 1 h before mechanical allodynia measurement. Data represent the frequency response to 0.16 g von Frey hair (VFH) stimulation. Each point represents the mean ± SEM of five to six mice. ^*p < 0.05 or ^**p < 0.01 denotes the significance level when compared with PBS-treated mice. ^##p < 0.01 denotes the significance level when compared with baseline (B) value without hair stimulation (one-way ANOVA followed by Student-Newman-Keuls test). The point 0 on the x-axis represents the measured mechanical allodynia immediately before drug treatment.

Figure 5.

Levels of expression of kinin B₁ receptor mRNA in the paw skin (A), sciatic nerve (B), spinal cord (C), and cerebral cortex (D) 7 d after sham surgery or partial sciatic nerve ligation (PSNL) in wild-type mice (+/+) assessed by real-time RT-PCR assay. All data have been normalized for levels of GAPDH expression within the same sample. Each bar represents the mean ± SEM of three to six mice. ^*p < 0.05 denotes the significance level when compared with the sham-operated group (Student's t test).

Figure 6.

A, Overt nociception produced by intraplantar injection of des-Arg⁹-bradykinin (DABK; 10 nmol per paw) in wild-type mice (+/+) 7 d after partial sciatic nerve ligation (PSNL). B, Difference in temperature [Δ Temperature (°C)] between ipsilateral and contralateral hindpaw surface observed 7 d after unilateral sciatic nerve lesion. Each point represents the mean ± SEM of four to six mice. ^**p < 0.01 denotes the significance level when compared with wild-type sham-operated group. ^##p < 0.01 denotes the significance level when compared with wild-type PSNL group (one-way ANOVA followed by Student-Newman-Keuls test).