The effect of spinal cord injury on the neurochemical properties of 3 vagal sensory neurons

41 The vagus nerve is comprised primarily of non-myelinated sensory neurons 42 whose cell bodies are located in the nodose ganglion (NG). The vagus has widespread 43 projections that supply most visceral organs, including the bladder. Due to its non-spinal 44 route, the vagus nerve itself is not directly damaged from spinal cord injury (SCI). 45 Because most viscera, including bladder, are dually innervated by spinal and vagal 46 sensory neurons, an impact of SCI on the sensory component of vagal circuitry may 47 contribute to post-SCI visceral pathologies. To determine if SCI, in male Wistar rats, 48 might impact neurochemical characteristics of NG neurons, immunohistochemical 49 assessments were performed for P2X3 receptor expression, IB4 binding, and 50 Substance-P expression, three known injury-responsive markers in sensory neuronal 51 subpopulations. In addition to examining the overall population of NG neurons, those 52 innervating the urinary bladder also were assessed separately. All three of the 53 molecular markers were represented in the NG from non-injured animals, with the 54 majority of the neurons binding IB4. In the chronically injured rats, there was a 55 significant increase in the number of NG neurons expressing P2X3 and a significant 56 decrease in the number binding IB4 compared to non-injured animals, a finding that 57 held true also for the bladder-innervating population. Overall, these results indicate that 58 vagal afferents, including those innervating the bladder, display neurochemical plasticity 59 post-SCI that may have implications for visceral homeostatic mechanisms and 60 nociceptive signaling. 61