Evidence that catecholamine-synthesizing perikarya in rat medulla oblongata do not contribute axons to the vagus nerve

We attempted to confirm reports that medullary catecholamine-synthesizing neurons in the rat contribute axons to the vagus nerve. Vagal preganglionic neurons in the medulla were identified by the retrograde intra-axonal transport of Fast Blue from the cervical vagus. Catecholamine-synthesizing neurons were identified using a specific antibody against tyrosine hydroxylase. A rhodamine-labelled second antibody was used to ensure that Fast Blue and tyrosine hydroxylase could be viewed entirely independently. We did not find any medullary neurons which contained both tyrosine hydroxylase and Fast Blue. Although further investigations by other laboratories are necessary, we believe that previous studies, using punctate versus diffuse horseradish peroxidase staining to doubly label neurons may have produced false positive results.