The paragigantocellular nucleus of the ventral medulla: a secondary source of cholinergic innervation of rat brainstem nuclei.

Many parts of the brainstem are known to be innervated by the cholinergic neurons of the pontomesencephalic tegmentum, but other possible sources of this innervation have rarely been considered. We sought to examine whether other cells in the brainstem were responsible for this cholinergic input using axonal tract tracing and choline acetyltransferase (ChAT) immunocytochemistry. The results confirm previous studies on the projections of the neurons of the pontomesencephalic tegmentum but also show that a group of ChAT-positive cells in the paragigantocellular nucleus in the ventral medulla are a source of widespread, albeit less substantial cholinergic projections to several areas of the brainstem.