Subcortical Afferents to the Nucleus Reticularis Tegmenti Pontis in the Rabbit: A Retrograde Horseradish Peroxidase Study

Abstract

Summary: The subcortical afferent projections to the nucleus reticularis tegmenti pontis (RT)were identified from the retrograde transport of horseradish peroxidase (HRP). HRP was injected into the medial and lateral parts of the RT, respectively. The major afferent inputs to the RT were found to arise ipsilaterally from the nucleus of the fields of Forel, the medial division of the medial mammillary nucleus, the region lateral to the red nucleus, and the posterior commissural nucleus; contralaterally from the anterior pretectal nucleus, the deep layer of the superior colliculus, and the supragenual nucleus; and bilaterally from the lateral habenular nucleus, the retrorubral nucleus, the central and posterior nuclei of the interpeduncular complex, the gray matter along the floor of the fourth ventricle, and the prepositus hypoglossi nucleus. Regions containing fewer labeled cells included the premammillary nucleus, the zona incerta, the nucleus pontis centralis oralis and the medial vestibular nucleus. In addition, the medial division of the medial mammillary nucleus, the lateral habenular nucleus, the central and posterior nuclei of the interpeduncular complex, and the supragenual nucleus were found to project mainly to the medial part of the RT. The superior colliculus, the retrorubral nucleus and the gray matter along the floor of the fourth ventricle projected mainly to the lateral part of the RT.These results indicate that the medial part of the RT receives fibers mainly from the diencephalic limbic areas, whereas the lateral part of the RT receives fibers mainly from nonlimbic (somatomotor, visuomotor and vestibular) areas.