Chemo-nociceptive signalling from the colon is enhanced by mild colitis and blocked by inhibition of transient receptor potential ankyrin 1 channels - PubMed
Chemo-nociceptive signalling from the colon is enhanced by mild colitis and blocked by inhibition of transient receptor potential ankyrin 1 channels
Martina Mitrovic et al. Br J Pharmacol.2010 Jul.
Abstract
Background and purpose: Transient receptor potential ankyrin 1 (TRPA1) channels are expressed by primary afferent neurones and activated by irritant chemicals including allyl isothiocyanate (AITC). Here we investigated whether intracolonic AITC causes afferent input to the spinal cord and whether this response is modified by mild colitis, morphine or a TRPA1 channel blocker.
Experimental approach: One hour after intracolonic administration of AITC to female mice, afferent signalling was visualized by expression of c-Fos in laminae I-II(o) of the spinal dorsal horn at sacral segment S1. Mild colitis was induced by dextran sulphate sodium (DSS) added to drinking water for 1 week.
Key results: Relative to vehicle, AITC (2%) increased expression of c-Fos in the spinal cord. Following induction of mild colitis by DSS (2%), spinal c-Fos responses to AITC, but not vehicle, were augmented by 41%. Colonic inflammation was present (increased myeloperoxidase content and disease activity score), whereas colonic histology, locomotion, feeding and drinking remained unchanged. Morphine (10 mg.kg(-1)) or the TRPA1 channel blocker HC-030031 (300 mg.kg(-1)) inhibited the spinal c-Fos response to AITC, in control and DSS-pretreated animals, whereas the response to intracolonic capsaicin (5%) was blocked by morphine but not HC-030031.
Conclusions and implications: Activation of colonic TRPA1 channels is signalled to the spinal cord. Mild colitis enhanced this afferent input that, as it is sensitive to morphine, is most likely of a chemonociceptive nature. As several irritant chemicals can be present in chyme, TRPA1 channels may mediate several gastrointestinal pain conditions.
Figures
Figure 1 Photomicrographs showing the expression of c-Fos in laminae I–IIo of the S1 spinal dorsal horn as visualized by immunohistochemistry 1 h after intracolonic administration of vehicle (peanut oil) or allyl isothiocyanate (AITC; 2%) to control mice and mice pretreated with dextran sulphate sodium (DSS; 2%) for 1 week. (A) Intracolonic vehicle in control mice, (B) intracolonic AITC in control mice, (C) intracolonic vehicle in DSS-pretreated mice, (D) intracolonic AITC in DSS-pretreated mice, (E) intracolonic AITC in control mice injected with HC-030031, (F) intracolonic AITC in DSS-pretreated mice injected with HC-030031. Calibration bar: 100 µm.
Figure 2 Quantitative estimates of c-Fos positive cells in laminae I–IIo of the S1 spinal dorsal horn as visualized by immunohistochemistry 1 h after intracolonic administration of (A) vehicle (peanut oil), 1% or 2% allyl isothiocyanate (AITC) and (B) vehicle or 5% capsaicin (Caps) in control mice. The values represent means + SEM, n = 5–16 (n = 16 for vehicle in panel A, combining the two vehicle groups run in parallel with the 1% AITC and the 2% AITC group, n = 5–7 for the other groups). **P < 0.01 (one-way
anova followed by Bonferroni's multiple comparison test), ++P < 0.01 (Student's t-test).
Figure 3 Myeloperoxidase (MPO) content of the distal colonic wall. (A) Colonic MPO content in control mice and mice pretreated with dextran sulphate sodium (DSS; 1 or 2%) for 1 week. DSS was added to the drinking water, whereas control mice drank normal tap water. (B) Colonic MPO content in mice pretreated with DSS (2%) for 1 week and treated with morphine (10 mg·kg−1 subcutaneously) or its vehicle 2 h before tissue collection. (C) Colonic MPO content in mice pretreated with DSS (2%) for 1 week and treated with HC-030031 (300 mg·kg−1) or its vehicle 1.5 h before tissue collection. The values represent means + SEM, n = 4–13 (n = 13 for control in panel A, combining the two control groups run in parallel with the 1% DSS and the 2% DSS group, n = 4 for the groups in panel C, n = 7 for the other groups). One outlier in panel A (control) and one outlier in panel C (HC-030031) were removed on the basis of Grubb's test. **P < 0.01 (one-way
anova followed by the Bonferroni's multiple comparison test).
Figure 4 Light microscopic appearance of the colonic mucosa taken from a control mouse (A) and a mouse pretreated with dextran sulphate sodium (2%) for 1 week (B). Calibration bar: 100 µm.
Figure 5 Time course of the circadian locomotor (A), exploratory (B), feeding (C) and drinking (D) activities in mice over a period of 2 weeks, before and after pretreatment with dextran sulphate sodium (DSS; 2%). During the first week, the mice drank normal tap water, whereas during the second week they drank water containing 2% DSS. The cumulative activities measured during the light (white areas) and dark (shaded areas) phases were expressed as a percentage of the activity measured during the dark phase of day 7, immediately before the pretreatment with DSS was begun. The values represent means ± SEM, n = 6. There were no significant differences between control and DSS-pretreated mice.
Figure 6 Quantitative estimates of c-Fos positive cells in laminae I–IIo of the S1 spinal dorsal horn as visualized by immunohistochemistry 1 h after intracolonic administration of (A) vehicle (peanut oil) and allyl isothiocyanate (AITC, 2%) in control mice and mice pretreated with 1% dextran sulphate sodium (DSS), (B) vehicle and AITC (2%) in control mice and mice pretreated with 2% DSS, and (C) vehicle and capsaicin (Caps, 5%) in control mice and mice pretreated with 2% DSS. DSS was added to the drinking water for 1 week, whereas control mice drank normal tap water. The values represent means + SEM, n = 5–7. +P≤ 0.1 (Student's t-test), **P < 0.01 (two-way
anova followed by Bonferroni's multiple comparison test).
Figure 7 Corticosterone levels in blood plasma as measured 2 days before (baseline) and 20 min after intracolonic administration of vehicle (peanut oil) and allyl isothiocyanate (AITC, 2%) to control mice and mice pretreated for 1 week with 2% dextran sulphate sodium (DSS). The values represent means + SEM, n = 6–7. One outlier in the control group treated with AITC (baseline) was removed on the basis of Grubb's test. **P < 0.01 (two-way repeated measures
anova followed by Bonferroni's multiple comparison test).
Figure 8 Effect of morphine on the quantitative estimates of c-Fos positive cells in laminae I–IIo of the S1 spinal dorsal horn as visualized by immunohistochemistry 1 h after intracolonic administration of (A) 2% allyl isothiocyanate (AITC) or (B) 5% capsaicin (Caps) to control mice and mice pretreated for 1 week with dextran sulphate sodium (DSS, 2%). Morphine (10 mg·kg−1) or its vehicle was injected subcutaneously 1 h before intracolonic administration of AITC or capsaicin. The values represent means + SEM, n = 5–7. +P≤ 0.1 (Student's t-test), *P < 0.05, **P < 0.01 (two-way
anova followed by Bonferroni's multiple comparison test).
Figure 9 Effect of HC-030031 on the quantitative estimates of c-Fos positive cells in laminae I–IIo of the S1 spinal dorsal horn as visualized by immunohistochemistry 1 h after intracolonic administration of (A) 2% allyl isothiocyanate (AITC) or (B) 5% capsaicin (Caps) to control mice and mice pretreated for 1 week with 2% dextran sulphate sodium (DSS). HC-030031 (300 mg·kg−1) or its vehicle was injected intraperitoneally 30 min before intracolonic administration of AITC or capsaicin. The values represent means + SEM, n = 5–6. +P≤ 0.1 (Student's t-test), *P < 0.05, **P < 0.01 (two-way
anova followed by Bonferroni's multiple comparison test).
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