Subnuclear organization of the lateral tegmental field of the rat. I: Nucleus ambiguus and ventral respiratory group.

Three classes of neurons within the lateral tegmental field of the rat medulla having different target projections were identified by retrograde labelling with three different fluorescent tracers. Labelled bulbospinal premotor and propriobulbar interneurons of the ventral respiratory group and vagal motoneurons of nucleus ambiguus formed partially intermingled longitudinal columns encompassed within a common region of the lateral tegmental field. Labelled neurons of each class were organized in a nonuniform distribution within these columns forming subdivisions distinguished by neuron morphology, orientation, and target projection. The three major rostrocaudal divisions of the ventral respiratory group (VRG) previously identified in the cat and rabbit were identified here in the rat, suggesting a common pattern of VRG organization among these species.