Projections from facial nucleus interneurons to the respiratory groups of brainstem in the rat.

Projections of the interneurons of the facial nucleus to respiration-related areas in the brainstem of the rat were revealed by unilateral, iontophorectic injection of the anterograde neuronal tracer, Phaseolus vulgaris leucoagglutinin (PHA-L), into the facial nucleus after motor neurons degeneration had been induced by axotomy of the facial nerve. Anterogradely labeled fibers and terminals were found bilaterally in the nucleus tractus solitarius, nucleus ambiguous and ventrolateral reticular formation in the medulla oblongata and ipsilaterally in the nucleus parabrachialis and nucleus Kolliker-Fuse in the pons. These results revealed that the interneurons in the facial nucleus have widespread projections to the respiratory groups in the brainstem, and suggest that the facial nucleus is involved not only in the control of muscles for facial expression but also in the regulation of functional respiratory activity.