An Orthograde Labelling Study of Axons of the Dorsal Motor Nucleus of the Vagus to Rat Cardiac Ganglia as Demonstrated by Autoradiography

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Abstract
Central organization of the cardiac vagus has not been clarified. Retrograde changes produced in medulla oblongata neurons after section of vagal branches has favored the dorsal motor nucleus of the vagus (DMNX). Current information concerning the origin, course, and termination of vagal preganglionic fibers within cardiac ganglia is conflicting. The explicit purpose of this study was to determine if vagal fibers originated specifically within the DMNX proper. Fibers within the cardiac ganglia were labelled with 3 H-leucine following injection into the DMNX. 12 adult albino rats were studied. DMNX were injected with 25 µCi 3H-leucine reconstituted to 5 µl. Animals were sacrificed by transcardial perfusion following a 4-day survival period. Serial cross-sections of the caudal pons, medulla oblongata, and thoracic viscera were processed for autoradiography. DMNX possessed a heavy incorporation of the radiochemical. Label was observed within the axons of the vagi. Cardiac ganglia contained labelled vagal fibers in close proximity to the postganglionic somata. Cardiac ganglia containing labelled preganglionic vagal axons were located in the cardiac plexuses and in the epicardium. Results show a labelled vagal preganglionic input to cardiac ganglia from the DMNX.