Brain stem localization of rodent esophageal premotor neurons revealed by transneuronal passage of pseudorabies virus

Background/Aims : Brain stem premotor neurons control swallowing through contacts with both afferent neurons and motoneurons. The location and connectivity of premotor neurons innervating the esophagus was determined using pseudorabies virus. Methods : In 30 rats, viral injections were made into either the cervical or subdiaphragmatic esophagus, cricothyroid muscle, or stomach. After a 48–62-hour survival, brain sections were processed immunocytochemically for the virus. Results : Neuronal labeling was limited to the compact formation of the nucleus ambiguus for survivals of 48–54 hours. At 57–62-hour survivals, virus-labeled second-order neurons (premotor neurons) were localized to the central subnucleus of nucleus of the solitary tract. Injections in the cricothyroid muscle and stomach resulted in distinct patterns of motoneuronal labeling in the nucleus ambiguus and dorsal motor nucleus and premotor neuronal labeling in the nucleus of the solitary tract. Conclusions : Virus-labeled premotor neurons in the nucleus of the solitary tract occurred as a result of retrograde transport of the virus from the nucleus ambiguus because no viral antigen was present in the tractus solitarius. The esophagus is controlled by a central circuit whereby esophageal vagal afferents terminate on premotor neurons in the central subnucleus that in turn innervate esophageal motoneurons in the nucleus ambiguus.