Projections of nucleus paragigantocellularis lateralis to locus coeruleus and other structures in rat.

The projections of the retrofacial portion of nucleus paragigantocellularis lateralis (retrofacial PGCL) were mapped in the rat with the Phaseolus vulgaris leucoagglutinin anterograde tracing technique. This structure projects to a restricted number of bulbar or spinal nuclei involved in autonomic regulation, principally the intermediolateral cell column of the spinal cord, the nucleus tractus solitarius complex, the lateral parabrachial and Kolliker-Fuse nuclei and the ventrolateral medulla. Retrofacial PGCL also densely innervates the locus coeruleus. This projection originates in large part from phenylethanolamine-N-methyltransferase-immunoreactive cells (C1 adrenergic cluster) as demonstrated by immunohistochemistry combined with the retrograde transport of rhodamine-tagged microbeads. A very small suprabulbar projection of retrofacial PGCL was also detected in some cases.