The efferent connections of the nucleus of the optic tract and the superior colliculus in the rabbit

Abstract

3H-leucine injections were made in tectal and pretectal areas in the rabbit. After injections in the nucleus of the optic tract (NOT) labeled fibers were distributed bilaterally to the superior colliculus, the dorsal part of the medial geniculate nucleus (MGd), and the pulvinar nucleus, and ipsilaterally to the external layer of the ventral lateral geniculate nucleus (LGv), the dorsal geniculate nucleus (LGd) pars beta, the reticular thalamic nucleus, and the lateral and medial terminal nucleus (LTN, MTN). Many labeled fibers were distributed to the lateral and some to the medial parts of the pontine nuclei. more caudally, coarse labeled fiber bundles descended ipsilaterally, distributing fibers to the prepositus hypoglossi and abducens nucleus and to the caudally adjoining medial reticular formation. Many labeled fibers were also present in the inferior olive, especially ipsilaterally in the dorsal cap and the ventrally adjoining pars beta, and a few in the contralateral dorsal cap area. Contralaterally, some descending fibers terminated in the dorsal part of the facial nucleus, in which motoneurons are located innervating the orbicularis oculi muscle. The superficial layers of superior colliculus distributed fibers bilaterally to the internal layer in the ventral lateral geniculate nucleus (LGv), the LGd alpha (lateral part), the MGd, the pulvinar, and more caudally to the ipsilateral parabigeminal and lateral pontine nuclei. The deep collicular layers distributed fibers ipsilaterally to MG (internal division), pulvinar, and the internal layer of LGv. Furthermore, ascending connections were found to the suprageniculate nucleus, the zona incerta, the mediodorsal nucleus, and some intralaminar and midline nuclei. Descending fibers terminated in the mesencephalic lateral tegmentum, pontine nuclei, and ventrally in the pontine and high medullary reticular formation. Contralaterally fibers were distributed to the nucleus reticularis tegmenti pontis (NRTP), the medial reticular formation, and the inferior olive just lateral to the nucleus beta. In one case fibers were also distributed to the lateral part of the contralateral facial nucleus in which motoneurons are located innervating the upper lip muscles.