Identification of premotor interneurons which project bilaterally to the trigeminal motor, facial or hypoglossal nuclei: a fluorescent retrograde double-labeling study in the rat.

With the aid of a fluorescent retrograde double-labeling technique, we examined in the rat the distribution of single neurons which project bilaterally to one of the orofacial motor nuclei (the trigeminal motor, facial and hypoglossal nuclei) by branching axons. The results suggested that premotor interneurons were distributed most frequently in the medial part of the parvicellular reticular nucleus; such neurons were further scattered in the other regions of the medullary reticular formation, in the regions around the trigeminal motor nucleus, in the parabrachial area, and in the mesencephalic reticular formation.