The relationship of the medullary catecholamine containing neurones to the vagal motor nuclei.

We have re-examined in the rat the nuclear localization of the medullary catecholamine-containing cell groups (A1 and A2) and their relation to the vagal motor nuclei using a double labeling method. The vagal nuclei were defined by the retrograde transport of horseradish peroxidase applied to the cervical vagus, and noradrenergic and adrenergic neurons were stained with the peroxidase-antiperoxidase immunocytochemical method using an antibody to dopamine beta-hydrolase. The method allows visualization of both labels within single neurons. The neurons of the A2 group are primarily distributed in both the nucleus of the solitary tract and the dorsal motor nucleus of the vagus in a complex interrelationship that depends on the rostrocaudal level. Caudal to the obex, cells of the dorsal motor nucleus of the vagus are scattered among cells immunoreactive for dopamine beta-hydroxylase in the area considered to be the commissural subnucleus of the nucleus of the solitary tract. At levels near and slightly rostral to the obex, the dopamine beta-hydroxylase-positive cells are largely confined to nucleus of the solitary tract. However, the rostral third of the A2 group lies predominantly within dorsal motor nucleus, as defined by horseradish peroxidase labeled cells, with only a few cells in the nucleus of the solitary tract. A subset of the dopamine beta-hydroxylase positive cells within the rostral dorsal motor nucleus of the vagus are also vagal efferents. Our results suggest that a second population of dopamine beta-hydroxylase positive vagal efferents may exist ventrolaterally where neurons of the AI cell group intermingle with those of nucleus ambiguus.