Ghrelin Modulation of CaV 2.2 Channels After Spinal Cord Injury

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Project Summary Gastrointestinal (GI) dysfunction after spinal cord injury (SCI) is a highly prevalent, but significantly understudied comorbidity that negatively impacts quality of life for individuals with SCI. Increasing evidence suggests impaired vagal activity is a primary cause of upper GI dysfunction after injury. Under normal conditions, gastric reflexes are coordinated by the vagus nerve. The vagus nerve contains both afferent fibers that convey sensory information to central structures and efferent fibers that carry motor output needed for gastric contractions. Previous work in our lab has demonstrated that following injury, vagal afferents are significantly less responsive to chemical stimuli, including the gut peptide ghrelin. Ghrelin is an orexigenic hormone that normally serves to decrease vagal afferent activity and increase gastric motility by binding to the growth hormone secretagogue receptor (GHSR1a), a G protein-coupled receptor, expressed along the vagal afferents. The cellular mechanisms underlying ghrelin’s ability to modulate vagal afferent activity in both healthy and disease states have yet to be fully elucidated. This proposal will utilize an animal model of SCI combined with molecular and imaging techniques, in vitro patch-clamp electrophysiology, and in vivo nerve recordings to identify mechanisms underlying the loss of vagal sensitivity post-SCI. The proposed experiments will investigate the central hypothesis that GHSR1a-mediated inhibition of calcium currents is dysregulated in gastric-projecting nodose ganglia neurons after SCI. Based upon our preliminary observations, we will test the hypothesis with two specific aims. Aim 1 will determine the precise mechanism underlying GHSR1a modulation of voltage-gated Ca2+ channels (CaV2.2 or N-type) in gastric-projecting vagal afferent neurons of naïve rats using whole-cell patch- clamp electrophysiology. Aim 2 will utilize immunohistochemistry, single-cell quantitative reverse transcription polymerase chain reaction (qRT-PCR), electrophysiological techniques, and in vivo nerve recordings to identify whether the GHSR1a-mediated effects of ghrelin on N-type Ca2+ channel currents and gastric vagal afferent excitability are dysregulated following SCI. This proposal will provide critical information regarding how changes to GPCR-mediated inhibition of CaV channels impairs gastric vagal afferent activity following injury. In addition, the proposed work will benefit future studies investigating the use of ghrelin mimetics to treat gastric dysmotility associated with a broad range of conditions including SCI, diabetes mellitus, and obesity.