Protease-Induced Excitation of Dorsal Root Ganglion Neurons in Response to Acute Perturbation of the Gut Microbiota is Associated with Visceral Hypersensitivity.

Abdominal pain is a major symptom of diseases associated with microbial dysbiosis. Disruption of the gut microbiota with antibiotics increases visceral pain, and germ-free mice are more prone to pain than conventionally-raised mice. However, the mechanisms underlying microbial modulation of pain remain elusive. We hypothesized that disruption of the intestinal microbiota modulates the excitability of peripheral nociceptive neurons. Patch clamp electrophysiological recordings of dorsal root ganglion (DRG) neuron excitability were obtained from control mice and mice treated with the non-absorbable antibiotic vancomycin (50 µg/ml in drinking water) for one week. Ten days prior to recording visceromotor response (VMR) telemetric transmitters were placed into the abdominal cavity of the mice and allowed to recover. VMR was measured by insertion of balloon catheter into the rectum under light anesthetization in both control and vancomycin treated mice, then distended to 80 mmHg and VMR recorded. Bacterial dysbiosis was verified by metagenomic analysis of stool microbial composition. Mice treated with vancomycin were more sensitive to colorectal distension in vivo (VMR increased by 70% at 80 mmHg compared to control), and DRG neurons from vancomycin-treated mice were hyperexcitable in vitro compared to water-treated controls (rheobase decreased by 30% relative to control). Interestingly, hyperexcitability of DRG neurons was not restricted to gut projecting neurons, suggesting a widespread effect of gut dysbiosis on pain pathways. Incubation of DRG neurons from naïve mice in serum from vancomycin-treated mice increased neuron excitability (rheobase decreased by 30% relative to control), suggesting that microbial dysbiosis alters circulating mediators that influence nociception. Multiplex ELISA measurements did not detect any significant changes in serum cytokines or chemokines between vancomycin-treated and control mice. The cysteine protease inhibitor E64 (30 nM) and the protease-activated receptor 2 (PAR2) antagonist GB-83 (10 µM) each blocked the increase in DRG neuron excitability in response to serum from vancomycin-treated mice. Naïve DRG neurons incubated with fecal supernatants from vancomycin-treated mice also exhibited increased excitability (rheobase decreased by 40% relative to control), but supernatants derived from colonic tissue failed to cause hyperexcitability. Overall, this data suggests that microbial dysbiosis within the gut alters pain sensitivity. This effect is not caused by inflammation or host derived factors, rather bacterially-derived cysteine proteases activating PAR2 on DRG neurons.