Projections from the nuclei prepositus hypoglossi and intercalatus to the superior colliculus in the cat: an anatomical study using WGA-HRP.

In view of the recognized role of the superior colliculus (SC) in eye and head movement, and following recent physiological studies, the presence of afferents to the SC from the vestibular complex and adjacent cellular groups were sought using axonal transport techniques. Injections of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) were made in the SC of 9 adult cats. Retrogradely labelled cells were observed in the nuclei prepositus hypoglossi (PH) and intercalatus (INT) predominantly contralaterally with only occasional cells in the medial (MVN) and descending (DVN) vestibular nuclei contralaterally. There appeared to be some topographical differences in anteroposterior distribution of labelled cells in the perihypoglossal nuclei after restricted SC injections. Two cases of intramedullary injection of WGA-HRP which involved the PH, INT, MVN and DVN revealed anterogradely labelled terminations in laminae IV and VI of the contralateral SC. A few additional labelled terminations were found in the medial portion of the contralateral medial geniculate body (MGB) and the nucleus of the optic tract-(NOT). The possible role of the perihypoglossal nuclear complex as a site of convergence of vestibular and neck afferent inputs destined for the SC is discussed.