Takehiko Umetani

Corticonuclear and corticovestibular projections from the uvula in the albino rat: differential projections from sublobuli of the uvula

The organization of the corticonuclear and corticovestibular projections from the uvula was investigated in the albino rat by an autoradiographic method. The corticonuclear fibers from sublobule a of the uvula terminated in the caudoventral part of the medial cerebellar nucleus, and the caudomedial part of the posterior interpositus nucleus with mediolateral topography. The medial and lateral portions of the sublobule projected to the medial cerebellar and posterior interpositus nuclei, respectively. The corticovestibular fibers from sublobule a terminated in the dorsal and rostral parts of the superior vestibular nucleus, the dorsal part of the lateral vestibular nucleus, and the caudomedial part of the spinal vestibular nucleus. However, the corticonuclear fibers from sublobuli b and c of the uvula terminated additionally in the ventromedial part of the lateral cerebellar nucleus, while the corticovestibular fibers from these sublobuli terminated additionally in the subnucleus y of the vestibular complex, with probable termination in the medial vestibular nucleus. The cortical region which sent efferent projections to the ventromedial part of the lateral cerebellar nucleus and the subnucleus y was located laterally in sublobuli b and c of the uvula. These differential projection patterns from the dorsal and ventral sublobuli suggest the difference of the functional correlates between the sublobuli in the uvula.

Efferent projections from the flocculus in the albino rat as revealed by an autoradiographic orthograde tracing method

The terminal sites of floccular efferent fibers were investigated in the albino rat by an autoradiographic orthograde method. The corticonuclear fibers terminated in the caudoventral part of the lateral cerebellar nucleus and in the caudoventral region of the lateral part of the posterior interpositus nucleus. A few fibers from the rostral flocculus terminated in the granular cell layer of the basolateral part of the nodulus and uvula as mossy fiber type terminals. The projection to the nodulus and uvula was confirmed, by an additional retrograde HRP study, to originate from scattered spindle-shaped cells in the floccular stalk. The corticovestibular fibers terminated massively in the subnucleus y. The fibers passing through the subnucleus y divided into two bundles; one bundle coursed rostrally to terminate in the lateral and ventral parts of the superior vestibular nucleus, while the other bundle passed through the lateral and then ventral parts of the lateral vestibular nucleus, supplying a few terminals to these regions, to terminate sparsely in the rostral to intermediate part of the medial vestibular nucleus and the rostroventral part of the spinal vestibular nucleus. Some fibers passing through the lateral vestibular nucleus coursed rostrally to terminate in the medial part of the superior vestibular nucleus. Sparse terminals derived from the rostral flocculus were found in the prepositus hypoglossal nucleus. No definitive differential efferent projections were demonstrated in the rat flocculus.

Cerebellar corticonuclear and corticovestibular fibers from the posterior lobe of the albino rat, with comments on zones.

The topographic organization of cerebellar cortical efferent fibers from the posterior lobe of the albino rat was studied by silver impregnation methods. The corticonuclear fibers from the vermis of the posterior lobe project to the caudomedial and middle parts of the medial cerebellar nucleus (MN) with medio-lateral localization; fibers from the medial portion of the vermis project to the caudomedial part of the MN (MNcm) and those from the lateral portion project to the middle part of the MN (MNm). Corticovestibular fibers originate in the caudal vermis lateral to the area projecting to the MNcm and MNm, and terminate in the dorsal part of the lateral vestibular nucleus (LVN). The origins of corticonuclear fibers to the dorsolateral protuberance of the MN (MNdlp), the posterior interpositus nucleus (PIN) and the anterior interpositus nucleus (AIN) are located latero-medially in the intermediate cortex. Fibers from the area adjacent to the vermis and rostral to the prepyramidal fissure project to the MNdlp, while those from the area lateral to the origin of the corticovestibular fibers and caudal to the fissure project to the medial AIN. Together, these areas comprise a medial portion of the intermediate cortex. Corticonuclear fibers to the PIN and lateral AIN originate from the lateral portion of the intermediate cortex. The corticonuclear fibers to the dorsolateral hump and lateral nucleus originate from the medial and lateral portions of the lateral cortex, respectively.

Topographic organization of the cerebellar nucleocortical projection in the albino rat: an autoradiographic orthograde study

The topography of the cerebellar nucleocortical projection was investigated in the albino rat by experiments employing an autoradiographic orthograde tracing method. The present results indicate that neurons in the deep cerebellar nuclei project to the granule cell layer of cerebellar cortex as mossy fiber terminals in an orderly way. Thus, the medial cerebellar nucleus projects mainly to the bilateral vermis with ipsilateral dominance. The interpositus and lateral cerebellar nuclei project mainly to the intermediate and lateral zones of the anterior and posterior lobes of the cortex, respectively. The paraflocculus and flocculus receive the nucleocortical projection from the caudal and ventral parts of the interpositus nuclei and the dentate nucleus. A mediolateral topography within each subdivision of the cerebellar nuclear complex was observed; the medial and lateral parts of the subdivision project to the more medial and lateral portions of the primary cortical targets of the subdivision, respectively.

Topographic Organization of the Corticonuclear and Corticovestibular Projections from the Pyramis and Copula pyramidis in the Albino Rat

The topographic organization of the corticonuclear and corticovestibular fibers from the pyramis and copula pyramidis in the albino rat was investigated by the autoradiographic orthograde tracing technique. Cortical efferent fibers from the medial part of the pyramis project to the caudoventral part of the caudomedial and middle subdivisions of the medial cerebellar nucleus, whereas those arising from the lateral part of the pyramis project to the caudomedial part of the posterior interpositus nucleus and also to the dorsal part of the lateral vestibular nucleus via the juxtarestiform body. Fibers from the medial part of the copula pyramidis project to the medial part of the anterior interpositus nucleus. On the other hand, fibers from the medial portion of the lateral part of the copula pyramidis project to the posterior interpositus nucleus, while those from the lateral portion, including the lateral limit of the copula pyramidis, project to the rostroventral part of the lateral cerebellar nucleus. These results indicate that the cortical efferent projections from the pyramis and the copula pyramidis are clearly oriented mediolaterally in the albino rat.

Topographic Organization of the Corticonuclear Fibers from the Tuber Vermis and Paramedian Lobule in the Albino Rat

The topographic organization of the corticonuclear fibers from the tuber vermis and paramedian lobule in the albino rat was investigated by autoradiographic anterograde tracing method. The medial portion of the tuber vermis projects to the dorsal part of the caudomedial subdivision of the medial cerebellar nucleus (MNcm), whereas the lateral portion of the tuber vermis projects to the dorsal part of the MNcm and the caudal part of the middle subdivision of the medial nucleus. The intermediate cortex of the paramedian lobule can be subdivided mediolaterally into three portions which project to the dorsolateral protuberance of the medial cerebellar nucleus, the rostrodorsal part of the posterior interpositus nucleus, and the caudodorsal part of the lateral anterior interpositus nucleus, respectively. The lateral cortex of the paramedian lobule can also be subdivided mediolaterally into two portions: the medial portion projects to the dorsolateral hump, and the lateral one to the lateral cerebellar nucleus. These results indicate that the cortical efferent fibers from the tuber vermis and paramedian lobule are clearly organized in the mediolateral direction in the albino rat.

Course of the accessory optic fascicular fibers in the rat

The courses of fibers in the dorsal and lateral fasciculi of the accessory optic tract were studied in the rat by means of a selective silver impregnation method for degenerating nerve fibers and Mesulams HRP method. The results indicate that except for a moderate number of fibers entering the dorsal terminal nucleus and the lateral terminal nucleus respectively, all optic fibers constituting the dorsal and lateral fasciculi descend the lateral surface of the brain to terminate in the medial terminal nucleus. No ascending optic nerve fiber to the dorsal or lateral terminal nucleus is included in these fasciculi.

Topographic Organization of the Corticonuclear Projections from the Paraflocculus in the Albino Rat: An Autoradiographic Orthograde Tracing Study

The topographic organization of corticonuclear projections from the paraflocculus was studied in rats by an autoradiographic orthograde tracing method. The corticonuclear fibers from the paraflocculus terminated primarily in the caudoventral part of the lateral cerebellar nucleus and in the lateral part of the posterior interpositus nucleus. The rostrolateral part of the ventral paraflocculus projected only to the lateral nucleus, and the caudomedial part projected only to the posterior interpositus nucleus. Although differential projections from the dorsal and ventral paraflocculi were not clearly observed, the dorsal paraflocculus appeared to project to slightly more dorsal parts of the lateral and posterior interpositus nuclei than did the ventral paraflocculus. The lateral, medial, rostral, and caudal parts of each sublobule tended to project to the ventral, dorsal, rostral, and caudal regions within the caudoventral part of the lateral nucleus, respectively, despite massive overlap in the individual terminal fields. The corticonuclear projection from the dorsal and ventral paraflocculi to the posterior interpositus nucleus were organized in different directions; those from the dorsal paraflocculus were organized rostrocaudally, while those from the ventral paraflocculus were organized mediolaterally. These results suggest that in rats the corticonuclear projections from the paraflocculus are topographically organized in the mediolateral and rostrocaudal directions as well as in the dorsoventral direction.