Identifying spinal sensory pathways activated by noxious esophageal acid

Abstract

The transient receptor potential vanilloid 1 (TRPV1) channel is critical for spinal afferent signaling of burning pain throughout the body. Such pain frequently originates from the esophagus, following acid reflux. The contribution of TRPV1 to spinal nociceptor signaling from the esophagus remains unclear. We aimed to identify the spinal afferent pathways that convey nociceptive signaling from the esophagus, specifically those sensitive to acid, and the extent to which TRPV1 contributes. Acid/pepsin (150mM HCl/1mgmL(-1) pepsin) or saline/pepsin was perfused into the esophageal lumen of anesthetized wild-type and TRPV1 null mice over 20min, followed by atraumatic perfuse fixation and removal of the cervical and thoracic spinal cord and dorsal root ganglia (DRG). To identify neurons responsive to esophageal perfusate, immunolabeling for neuronal activation marker phosphorylated extracellular receptor-regulated kinase (pERK) was used. Labeling for calcitonin gene-related peptide (CGRP) and isolectin B4 (IB4) was then used to characterize responsive neurons. Esophageal acid/pepsin perfusion significantly increased the number of pERK-immunoreactive (IR) neurons in the DRG and the cervical and thoracic spinal cord dorsal horn (DH) relative to saline/pepsin (DRG P<0.01; cervical DH P<0.05 and thoracic DH P<0.005). The number of pERK-IR neurons following acid perfusion was significantly attenuated in TRPV1 -/- mice (DH P<0.05 and DRG P<0.05). This study has identified populations of spinal afferent DRG neurons and DH neurons involved in signaling of noxious acid from the esophagus. There is a major contribution of TRPV1 to signaling within these pathways.