Evidence for cerebellar efferents to the ventral lateral geniculate nucleus and the lateral terminal nucleus of the accessory optic system in the rabbit. A morphological study with comments on the organizational features of visuo-oculomotor-trunco-cerebellar loops.
The efferent ascending connections of the cerebellar nuclei and afferent optic projections to the ventral lateral geniculate nucleus and the terminal nuclei of the accessory optic tract were traced in the 26 rabbits using the technique of experimental anterograde degeneration. Following eyeball enucleation, within the ventral lateral geniculate nucleus terminal degeneration was found mostly contralaterally and was restricted to both the sublayers (external and internal) of the lateral division, while ipsilaterally only scanty and confined to the dorsal region of the external sublayer of the lateral (sector alpha) division. After cerebellar lesions degeneration was found within the ventral region of the medial division (sector gamma) of the contralateral LGv and within contralateral LTN. From the localization of the lesions in the cerebellar nuclei, as well as from the distribution of degenerations in the area of the LGv, it was postulated that the parent neurons for the cerebello-LGV fibers are located in the contralateral posterior interposed nucleus, although the anteroventral lateral cerebellar nucleus, the Y group and the infracerebellar nucleus have been not excluded. Within the all terminal nuclei of the accessory optic tract the retinal fibers were found to terminate bilaterally with contralateral preponderance, mostly in the MTN, while ipsilateral fibers terminate most extensively in the lateral terminal nucleus of the accessory optic tract (LTN). In this means the retinal afferents of both sides seem to subserve the contralateral lateral cerebellar nucleus control. Taken together, the findings indicate that the extrageniculate visual inputs might be subjected to direct reciprocal cerebello-nuclear control. The visual extrageniculate cerebellopetal pathways and their correlations with the vestibulo-ocular and optokinetic reflex loops are discussed.
D000818:Animals; D001931:Brain Mapping; D002529:Cerebellar Nuclei / Q000033:anatomy & histology*; D005133:Eye Movements; D005829:Geniculate Bodies / Q000033:anatomy & histology*; D009410:Nerve Degeneration; D009412:Nerve Fibers / Q000648:ultrastructure; D009474:Neurons / Q000648:ultrastructure; D009802:Oculomotor Nerve / Q000033:anatomy & histology; D009900:Optic Nerve / Q000033:anatomy & histology*; D011149:Pons / Q000033:anatomy & histology; D011817:Rabbits; D012018:Reflex / Q000502:physiology; D012160:Retina / Q000033:anatomy & histology; D014726:Vestibular Nuclei / Q000033:anatomy & histology; D014793:Visual Cortex / Q000033:anatomy & histology; D014795:Visual Pathways / Q000033:anatomy & histology; D014796:Visual Perception / Q000502:physiology*