Modulation of Spinal Afferent Neuronal Structure and Function in Diseases Associated with Abdominal Pain

Abstract

Background: Abdominal pain is a primary symptom of many gastrointestinal diseases, including irritable bowel syndrome (IBS) and pancreatic ductal adenocarcinoma (PDAC). Many mediators have been implicated in the pathophysiology of these diseases and the development of abdominal pain, a phenomenon whose main feature is its vague localization. Emerging therapeutic targets for IBS are changes in diet and the release of specific microbial mediators, which can trigger symptoms of pain. Additionally, neurotrophins of the GDNF family and their RET receptors have been implicated in the development of neural invasion by pancreatic tumor cells, a process which has been linked to abdominal pain and decreased survival in cancer patients. Aims and Methodology: Patch clamp electrophysiology experiments were performed on DRG neurons incubated with fecal supernatant (FS) from IBS patients to determine the mechanisms behind a low FODMAP diet-microbiota interaction in the pathology of this disease. Retrograde tracing experiments were performed on C57Bl/6 mice using fluorescent neuron tracers to determine the extent of overlap in receptive fields of colon-projecting DRG neurons, a feature which can exacerbate and contribute to the vague localization of abdominal pain. Lastly, following treatment with conditioned media from PDAC cell lines (PanC1 and MiaPaCa-2) changes in DRG neuron morphology were quantified using Sholl analysis to determine if RET ligands released by PDAC cell lines have a neurotrophic effect on DRG neurons, facilitating neural invasion. Results: Spinal afferent neurons become more excitable following treatment with IBS-D patient FS, and lowering FODMAP intake reduces pain severity and mitigates the excitatory effect of patient FS. The underlying mechanisms in FS-induced hyperexcitability is a decreased leak K+ conductance triggered by activation of PAR2 receptors via cysteine proteases. Retrograde tracing revealed dual-innervation of the proximal and distal regions of the colon by individual extrinsic afferent neurons. Lastly, RET ligands secreted by PanC1 and MiaPaCa-2 cell lines lead to increases in DRG neurite branching and length via RET receptor activation, an event which could facilitate the development of neural invasion. Conclusion: Taken together, this data provides a more thorough understanding of the role of spinal afferent neurons in health and disease.