Projection of nodose ganglion cells to the upper cervical spinal cord in the rat

Afferent fibers mediating pain from myocardial ischemia classically are believed to travel in sympathetic nerves to enter the thoracic spinal cord. After sympathectomies, angina pectoris still may radiate to the neck and inferior jaw. Sensory fibers from those regions are thought to enter the central nervous system through upper spinal cord segments. We postulated that axons from nodose ganglion cells might project to cervical cord segments. The purpose of this study was to determine the density and pathway of vagal afferent innervation to the upper cervical spinal cord. Following an injection of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) into the upper cervical spinal cord, approximately 5.8% of cells in the nodose ganglion contained reaction product. Cervical vagotomy did not diminish the density of WGA-HRP labeled cells in the nodose ganglion. However, a spinal cord hemisection cranial to the injection site eliminated labeling of nodose cells. These data indicate that a portion of vagal afferent neurons project from the nodose ganglion to the upper cervical spinal cord. In addition, vagal afferent fibers reach the spinal cord via a central route rather than through dorsal root ganglia.