The role of transient receptor potential vanilloid 1 in mechanical and chemical visceral hyperalgesia following experimental colitis

Abstract

The transient receptor potential vanilloid 1 receptor (TRPV1) is an important nociceptor involved in neurogenic inflammation. We aimed to examine the role of TRPV1 in experimental colitis and in the development of visceral hypersensitivity to mechanical and chemical stimulation. Male Sprague-Dawley rats received a single dose of trinitrobenzenesulfonic acid (TNBS) in the distal colon. In the preemptive group, rats received the TRPV1 receptor antagonist JYL1421 (10 mumol/kg, i.v.) or vehicle 15 min prior to TNBS followed by daily doses for 7 days. In the post-inflammation group, rats received JYL1421 daily for 7 days starting on day 7 following TNBS. The visceromotor response (VMR) to colorectal distension (CRD), intraluminal capsaicin, capsaicin vehicle (pH 6.7) or acidic saline (pH 5.0) was assessed in all groups and compared with controls and naïve rats. Colon inflammation was evaluated with H&E staining and myeloperoxidase (MPO) activity. TRPV1 immunoreactivity was assessed in the thoraco-lumbar (TL) and lumbo-sacral (LS) dorsal root ganglia (DRG) neurons. In the preemptive vehicle group, TNBS resulted in a significant increase in the VMR to CRD, intraluminal capsaicin and acidic saline compared the JYL1421-treated group (P<0.05). Absence of microscopic colitis and significantly reduced MPO activity was also evident compared with vehicle-treated rats (P<0.05). TRPV1 immunoreactivity in the TL (69.1+/-4.6%) and LS (66.4+/-4.2%) DRG in vehicle-treated rats was increased following TNBS but significantly lower in the preemptive JYL1421-treated group (28.6+/-3.9 and 32.3+/-2.3 respectively, P<0.05). JYL1421 in the post-inflammation group improved microscopic colitis and significantly decreased the VMR to CRD compared with vehicle (P<0.05, >/=30 mm Hg) but had no effect on the VMR to chemical stimulation. TRPV1 immunoreactivity in the TL and LS DRG was no different from vehicle or naïve controls. These results suggest an important role for TRPV1 channel in the development of inflammation and subsequent mechanical and chemical visceral hyperalgesia.

Figure 1

Summary data of the mean VMR to CRD following TNBS in rats treated with pre-emptive vehicle or JYL1421 and post-inflammation vehicle or JYL1421. A. The VMR significantly increased at distension pressures ≥ 30mmHg one week following intracolonic TNBS in the vehicle treated group (*p<0.05 vs. baseline) indicating the development of visceral hyperalgesia. There was no difference in the VMR in the rats that received pre-emptive JYL1421 (10μmol/kg, i.v.) when compared to baseline. B. The VMR significantly increased at distension pressures ≥ 30mmHg two week following TNBS in the vehicle control group (*p<0.05 vs. baseline). The VMR in the post-inflammation JYL1421 group remained significantly higher than baseline at CRD pressures > 30mmHg (*p<0.05 vs baseline VMR), but the response was significantly less than the vehicle treated group at CRD pressures of 30, 40 and 60mmHg (#p<0.05 vs post-inflammation vehicle).

Figure 2

Summary data of mean VMR to acute intraluminal capsaicin vehicle (pH 6.7), acidic saline (pH 5.0) or capsaicin following TNBS in rats treated with pre-emptive vehicle or JYL1421 and post-inflammation vehicle or JYL1421. A. There was no difference in the response to intraluminal capsaicin vehicle in rats in the pre-emptive groups when compared to naïve rats. Rats that received intracolonic TNBS with preemptive vehicle (i.v.) exhibited a significantly greater response to intraluminal acidic saline and capsaicin (0.015mg) compared to naïve rats and pH 6.7 vehicle. However, animals treated with pre-emptive JYL1421 did not exhibit any significant increase in VMR to intraluminal acidic saline or capsaicin compared to naïve and were significantly lower than JYL1421 vehicle treated (* p<0.05 vs naïve and pH 6.7 vehicle, # p<0.05 vs JYL1421 vehicle). B. There was no difference in the response to intraluminal capsaicin vehicle in rats in the post-inflammation groups when compared to naïve rats. (p>0.05). Rats that received JYL1421 vehicle post-inflammation exhibited a significantly greater response to intraluminal acidic saline and capsaicin (0.015mg) compared to naïve rats. Similarly, animals treated with JYL1421 post-inflammation continued to exhibited a significantly higher response to intraluminal acidic saline and capsaicin compared to naïve (*p<0.05).

Figure 3

Acute effects of JYL1421 on mechanical distension and intraluminal capsaicin in pre-emptive vehicle rats. A. The VMR significantly increased at distension pressures ≥ 30mmHg one week following TNBS in the pre-emptive vehicle group (*p<0.05 vs. baseline). There was no difference in the VMR in the rats that received JYL-1421 (10μmol/kg, iv) 15 minutes prior the second VMR. B. The increased response to intraluminal capsaicin (0.03mg) in rats that received TNBS with pre-emptive vehicle was significantly attenuated by acute dosing of JYL1421 (10μmol/kg, iv) given 15 minutes prior to intraluminal capsaicin (* p<0.05).

Figure 4

A. Hematoxylin and eosin staining of distal colon one week following TNBS administration. TNBS-treated rats demonstrated destruction of the epithelium with prominent neutrophilic infiltrates in the JYL1421 vehicle treated rats (a) 10X and (b) 20X. Pretreatment with JYL1421 prevented the epithelial damage in the distal colon and decreased the inflammatory infiltrates (c) 10X and (d) 20X. B. Staining of the distal colon in the post inflammation groups (two weeks following intracolonic TNBS). Rats continued to demonstrate destruction of the epithelium with prominent mixed inflammatory infiltrates in the JYL1421 vehicle treated rats (e) 10X and (f) 20X. Post-inflammation treatment with JYL1421 improved the epithelial damage in the distal colon and decreased the inflammatory infiltrates (g) 10X and (h) 20X. Scale bar, 100μm.

Figure 5

Bar graph represents the MPO activity in the distal colon following intracolonic TNBS. The MPO activity was significantly lower in rats with pre-emptive administration of JYL1421 compared to vehicle controls (*p<0.05). There was no difference in the MPO activity in the post-inflammation JYL1421 group compared to vehicle control.

Figure 6

Percentage of TRPV1–immunoreactive neurons per total DRG neuronal profile in the thoracolumbar (T13-L1) and lumbosacral (L6-S1) spinal segments in naïve and TNBS treated rats. A. Following TNBS there was a significant increase in the TRPV1 immunoreactivity in the vehicle treated groups (*p<0.05 vs naive). Pre-emptive administration of JYL1421 significantly decreased the TRPV1 expression when compared to naïve and vehicle treated rats (#p<0.05). B. There was no difference in the TRPV1 immunoreactivity in the post-inflammation JYL1421 and vehicle treated group when compared to naïve (p>0.05 vs naive).

Figure 7

TRPV1 expression in the T13- L1 DRG in naïve rats (A and D) and following intracolonic TNBS. The proportion of TRPV1-immunoreactive neurons (green) is increased following inflammation with TNBS in the JYL1421 vehicle treated rats (B) and is prevented by pre-emptive administration of JYL1421(C). TRPV1 expression returned to baseline in the post-inflammation vehicle control (E) and was no different than JYL1421 treated rats (F). Scale bar, 100μm.