Pathogenesis of abdominal pain in bowel obstruction: Role of mechanical stress-induced upregulation of nerve growth factor in gut smooth muscle cells

Abstract

Abdominal pain is one of the major symptoms in bowel obstruction (BO); its cellular mechanisms remain incompletely understood. We tested the hypothesis that mechanical stress in obstruction upregulates expression of nociception mediator nerve growth factor (NGF) in gut smooth muscle cells (SMC), and NGF sensitizes primary sensory nerve to contribute to pain in BO. Partial colon obstruction was induced with a silicon band implanted in the distal bowel of Sprague-Dawley rats. Colon-projecting sensory neurons in the dorsal root ganglia (DRG, T13 to L2) were identified for patch clamp and gene expression studies. Referred visceral sensitivity was assessed by measuring withdrawal response to stimulation by von Frey filaments (VFF) in the lower abdomen. Membrane excitability of colon-projecting DRG neurons was significantly enhanced, and the withdrawal response to VFF stimulation markedly increased in BO rats. The expression of NGF mRNA and protein was increased in a time-dependent manner (day 1 to day 7) in colonic SMC, but not in mucosa/submucosa of the obstructed colon. Mechanical stretch in vitro caused robust NGF mRNA and protein expression in colonic SMC. Treatment with anti-NGF antibody attenuated colon neuron hyper-excitability and referred hypersensitivity in BO rats. Obstruction led to significant increases of tetrodotoxin-resistant (TTX-r) Na ⁺ currents and mRNA expression of Na _v1.8, but not Na _v1.6 and Na _v1.7 in colon neurons; these changes were abolished by anti-NGF treatment. In conclusion, mechanical stress-induced upregulation of NGF in colon SMC underlies the visceral hypersensitivity in BO through increased gene expression and activity of TTX-resistant Na ⁺ channels in sensory neurons.