Commensal microbiota is fundamental for the development of inflammatory pain

Abstract

The ability of an individual to sense pain is fundamental for its capacity to adapt to its environment and to avoid damage. The sensation of pain can be enhanced by acute or chronic inflammation. In the present study, we have investigated whether inflammatory pain, as measured by hypernociceptive responses, was modified in the absence of the microbiota. To this end, we evaluated mechanical nociceptive responses induced by a range of inflammatory stimuli in germ-free and conventional mice. Our experiments show that inflammatory hypernociception induced by carrageenan, lipopolysaccharide, TNF-alpha, IL-1beta, and the chemokine CXCL1 was reduced in germ-free mice. In contrast, hypernociception induced by prostaglandins and dopamine was similar in germ-free or conventional mice. Reduction of hypernociception induced by carrageenan was associated with reduced tissue inflammation and could be reversed by reposition of the microbiota or systemic administration of lipopolysaccharide. Significantly, decreased hypernociception in germ-free mice was accompanied by enhanced IL-10 expression upon stimulation and could be reversed by treatment with an anti-IL-10 antibody. Therefore, these results show that contact with commensal microbiota is necessary for mice to develop inflammatory hypernociception. These findings implicate an important role of the interaction between the commensal microbiota and the host in favoring adaptation to environmental stresses, including those that cause pain.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.

Mechanical hypernociception and edema formation induced by injection of carrageenan, LPS, or formalin in germ-free (GF, open symbols) or conventional (CV, filled symbols) mice. (A) Time–response curve of hypernociception induced by i.pl. injection of 30 μl of carrageenan (squares, 100 μg per paw) or 30 μl of saline (circles, vehicle). The hypernociceptive effects were determined at 1, 3, and 5 h after injection. (B) Time-response curve of hypernociception induced by i.pl. injection of 30 μl of LPS (squares, 100 ng per paw) or 30 μl saline (circles, vehicle). (C) Nociceptive responses induced by i.pl. injection of formalin (2%; 30 μl per paw) or 30 μl of saline (vehicle). The nociceptive responses were determined from 0 to 5 min and from 15 to 30 min after formalin injection. Results are expressed by the mean ± SEM of at least six animals per group. *, P < 0.05 when comparing GF and CV mice.

Fig. 2.

Production of TNF-α, IL-1β, and CXCL1 and recruitment of neutrophils after injection of carrageenan in GF (open bars) or CV (filled bars) mice. (A–C) Concentrations of TNF-α (A), IL-1β (B), and CXCL1 (C) in paws injected with 100 μg of Cg or saline (vehicle). (D) Recruitment of neutrophils in soft paw tissue injected with 100 μg of Cg or saline (vehicle). Mice were culled 1, 3, and 5 h after injection, and soft paw tissue was used to measure cytokines by ELISA and neutrophil influx by myeloperoxidase. Results are expressed as the mean ± SEM of five animals per group. *, P < 0.05 when comparing GF and CV mice.

Fig. 3.

Mechanical hypernociception induced by TNF-α, IL-1β, CXCL1, PGE2, and dopamine in GF (open symbols) and CV (filled symbols) mice. Time–response curves of hypernociception induced by i.pl. injection of the mediators (squares) TNF-α (100 pg per paw), IL-1β (100 pg per paw), CXCL1 (10 ng per paw), prostaglandin E2 (PGE2; 100 ng per paw), dopamine (Dopa; 10 μg per paw), or vehicle (circles, 30 μl saline). Results are expressed as the mean ± SEM of six animals per group. Asterisks denote statistically significant differences compared with the control group (P < 0.05).

Fig. 4.

Reversion of antihypernociceptive phenotype of GF (open bars) mice compared with CV (filled bars) ones. (A) Two weeks after feces administration (10 mg/kg; by oral gavage) from conventional or germ-free mice, mechanical hypernociception induced by i.pl. injection carrageenan (100 μg per paw) was evaluated in GF mice and compared with CV and GF vehicle-treated. (B) Then, 48 h after systemic LPS administration (1 mg/kg; s.c.), mechanical hypernociception induced by i.pl. injection of carrageenan (100 μg per paw) was evaluated in GF mice and compared with CV and GF vehicle-treated. The hypernociceptive responses were taken 3 h after carrageenan injection. The results are expressed by the mean ± SEM of at least five animals per group. Asterisks denote statistically significant differences compared with the control group (P < 0.05).

Fig. 5.

IL-10 mediates the diminished hypernociceptive response of GF mice. (A) CV mice were injected with recombinant murine IL-10 (100 ng per paw, s.c.) before the injection of carrageenan (100 μg per paw). (B) Expression of IL-10 as measured by quantitative PCR in paw skin of CV and GF mice after i.pl. injection of carrageenan (100 μg per paw). (C) GF or CV mice were treated with a monoclonal anti-IL-10 antibody (50 μg per mouse, s.c.) or control antibody (50 μg per mouse) and hypernociception after i.pl. injection of carrageenan (100 μg per paw) evaluated 40 min later. Data are mean ± SEM of measurements of at least five mice per group (except in B) and are from one of two representative experiments performed.