Catecholamine innervation of the rat hypoglossal nucleus

The catecholamine innervation of the hypoglossal nucleus (XII) was investigated immunocytochemically by comparing the distribution patterns of tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH) and phenylethanolamine N-methyltransferase (PNMT) in the rat. Numerous TH- and DBH-positive profiles were found throughout XII, while only occasional PNMT immunoreactivity was observed. Significantly, the distribution patterns of TH and DBH immunoreactivity were coextensive with the most intense staining found ventromedially along the caudal half of XII. We conclude, therefore, that the catecholamine innervation of XII is largely noradrenergic, and that motoneurons innervating the genioglossi muscles, the principal protrusors of the tongue, are the primary targets of this input.