Tadashi Kawasaki

Afferent projections from the brainstem to the three floccular zones in cats. I. Climbing fiber projections

The cats flocculus can be divided into 3 zones on the basis of differences in their efferent projection sites. In the present study, climbing fiber projections from the inferior olive to each zone of the flocculus were studied by means of retrograde axonal transport of horseradish peroxidase (HRP). Following large injections of HRP into the flocculus, labeled cells appear in the dorsal cap and the ventrolateral outgrowth of the principal olive. No HRP-labeled somata are present in other parts of the inferior olive. Following microinjections of HRP into the rostral of caudal zones of the flocculus, labeled cells appear in the ventrolateral outgrowth and the rostral part of the dorsal cap, while, after injections into the middle zone, labeled cells are found in the caudal part of the dorsal cap. These findings show that there exists zonal organization in the climbing fiber projections to the flocculus; the rostral and caudal zones receive climbing fiber afferents from the ventrolateral outgrowth and the rostral part of the dorsal cap, while the middle zone receives those from the caudal part of the dorsal cap.

Role of the nucleus of the optic tract in monkeys in relation to optokinetic nystagmus

Nine monkeys were used in order to clarify the role of the nucleus of the optic tract (NOT) in the generation of optokinetic nystagmus (OKN). In 3 monkeys whose NOTs were almost totally damaged, optokinetic stimulus toward the lesioned side failed to generate either eye deviation or OKN and revealed only voluntary saccades, whereas that toward the side contralateral to the lesion generated normal gain of OKN. The phenomenon was identical in either monocular or binocular stimulation. In two of 3 monkeys whose NOTs were partially destroyed, optokinetic stimulus toward the lesioned side produced OKN, but the gain of OKN, but the gain of OKN was at maximum less than 60% in both binocular and monocular stimulation. In the remaining one monkey whose NOT was injured, but superficially, OKN showed normal gain in both directions. In 3 other monkeys whose NOTs were spared, this OKN asymmetry was not observed. Pursuit and saccadic eye movements were normal in all NOT-lesioned monkeys. Visually induced eye movements in the vertical axis were likewise normal. The present experiment suggests that the NOT in monkeys may be the first relay station in the horizontal optokinetic path and that in primates as in non-primates both crossed and uncrossed fibers reach motor centers for OKN via the NOT.

Topographical distribution of Purkinje cells in the uvula and the nodulus projecting to the vestibular nuclei in cats

The localization of the Purkinje cells in the uvula and nodulus projecting to the vestibular nuclei and the prepositus hypoglossal nucleus (PH) was studied by means of retrograde axonal transport of horseradish peroxidase in cats. Findings indicate a zonal organization in the uvula and nodulus projecting to the vestibular nuclei as follows; the Purkinje cells located in the medial half of the uvula except for the area along the posterolateral fissure project to the middle part of the inferior vestibular nucleus (IV) (middle IV zone); those in the lateral half of the uvula other than the laterocaudal part project to the caudal part of the IV (caudal IV zone); those in the mediorostral part of the nodulus and the middle part of the nodulus project to the middle part of the medial vestibular nucleus (MV) (middle MV zone); those in the lateral part of the nodulus project to the caudal part of the MV (caudal MV zone); those in the medial part of the uvula and nodulus along the posterolateral fissure project to the dorsal peripheral part of the superior vestibular nucleus (SV) (SV zone). There is no specific projection zone in the uvula and nodulus projecting to the lateral vestibular nucleus, the ventral peripheral and the central part of the SV, the rostral part of the MV, the rostral part and the caudal pole of the IV, the caudal one-third of the group f, the group x and the PH.

Neuronal pathway from floccular caudal zone contributing to vertical eye movements in cats--role of group y nucleus of vestibular nuclei.

In ketamine-anesthetized cats, electric microstimulation of the group y nucleus of the vestibular nuclei evoked a slow and smooth upward eye movement. Destruction of the group y nucleus eliminated a slow and smooth downward eye movement evoked by stimulation of the caudal zone of the flocculus. These data support the interpretation that Purkinje cell activity in the caudal zone of the flocculus can evoke vertical eye movements by inhibiting the activity of neurons of the group y nucleus.

Zonal organization of the floccular Purkinje cells projecting to the vestibular nucleus in cats

Injections of horseradish peroxidase (HRP) were made iontophoretically in the vestibular nuclear complex and the prepositus hypoglossal nucleus (PH) in cats. Differential localization of labeled Purkinje cells due to the retrograde axonal transport of HRP was studied in the flocculus. It was found that there existed three-dimensional zones which were perpendicular to the long axis of the folia in the ipsilateral flocculus; Purkinje cells projecting to the superior vestibular nucleus were distributed in the rostral zone, those to the medial vestibular nucleus in the middle zone. Specific projection-zones to the inferior vestibular nucleus, lateral vestibular nucleus and the PH were not found. Only a small number of labeled Purkinje cells were scattered in the flocculus after injection of HRP in them.

Identification of the Purkinje cell/climbing fiber zone and its target neurons responsible for eye-movement control by the cerebellar flocculus

We identified 3 Purkinje cell/climbing fiber zones in the cat cerebellar flocculus. The zones were perpendicular to the long axes of the crooked floccular folia, forming the crooked zones. Each zone was different in axonal projection areas of its target neurons. From the neuronal networks it is theoretically expected that activity changes of a particular zone control eye movement in a particular plane: (1) the rostral and caudal zones on one side control movement in the anterior canal plane on the side of the activity changes and those on both sides control movement in all vertical planes from sagittal to transverse planes; and (2) the middle zone controls movement in the horizontal plane by reciprocal activity changes on both sides. The zone-specific climbing fiber input to a particular zone may contribute to activity changes of the zone in response to mossy fiber input spreading across several zones. Electrical stimulation of each zone evoked the same pattern of eye movement as that theoretically expected from the neuronal networks. This is the first indication that there are indeed functional differences between the Purkinje cell zones in the cerebellum. Our findings support Oscarssons proposal that each Purkinje cell/climbing fiber zone plus its target neurons may be an operational unit for control of a given motor function.

Zonal organization of the floccular Purkinje cells projecting to the group y of the vestibular nuclear complex and the lateral cerebellar nucleus in cats

Abstract Injections of horseradish peroxidase (HRP) were made iontophoretically in the group y of the vestibular nucleus and the lateral cerebellar nucleus (LC) in cats. Topographical distribution of labeled Purkinje cells due to the retrograde axonal transport of HRP was studied in the flocculus. It was found that Purkinje cells in the caudal part of the flocculus project mainly to the ipsilateral group y and sparsely to the ventromedial part of the ipsilateral LC.

Functional localization in the three floccular zones related to eye movement control in the cat

Anatomically, the cats cerebellar flocculus can be divided into 3 zones on the basis of differences in their efferent projection sites. The functional differences of these 3 zones in relation to eye movement control were investigated by observing the eye movements evoked by electric stimulation of each zone of the flocculus in ketamine-anesthetized cats. Stimulation of the flocculus elicited a slow eye movement. The direction of the slow eye movement was mapped. A downward eye movement was evoked by stimulation of the caudal zone. An ipsilateral horizontal eye movement was induced from the middle zone. An upward eye movement was elicited from the rostral zone. When prolonged stimulation was applied to the flocculus, the slow eye movement was followed by nystagmus in the opposite direction. This nystagmus persisted for many seconds after cessation of stimulation (afternystagmus). Nystagmus and afternystagmus could not be elicited in deeply anesthetized cats. Possibilities as to how the stimulation leads to various eye movements are discussed.

Afferent projection from the dorsal nucleus of the raphe to the flocculus in cats

Horseradish peroxidase (HRP) was injected iontophoretically into the cerebellar flocculus in cats. The neurons labeled with HRP were recognized in the caudal part of the dorsal nucleus of the raphe. Electrical stimulation of this region elicited orthodromic evoked potentials in the flocculus and stimulated sites of low threshold current necessary to evoke the responses were limited in a small area corresponding well with the dorsal nucleus of the raphe.

Mossy fiber projections from the brain stem to the nodulus in the cat. An experimental study comparing the nodulus, the uvula and the flocculus.

Mossy fiber projections from the brainstem to the nodulus were studied by means of the retrograde transport of horseradish peroxidase (HRP) in the cat. The findings indicate exclusive secondary vestibular projections to the nodulus (96.5% of the total number of labeled cells in cat 1). Major sources of such projections include the caudal half of the medial and inferior vestibular nuclei, and the dorsal half of the superior vestibular nucleus. Groups-x and -z of the vestibular nuclei give rise to minor projections. The projections from groups-f and -y, and the interstitial nucleus of the eighth nerve are very few, if any. Minor extravestibular projections originate from the prepositus hypoglossal nucleus and the infratrigeminal nucleus. All these projections are bilateral. No other nuclei in the brainstem were labeled following HRP injection in the nodulus. No indications of mediolateral and dorsoventral differences in mossy fiber projections were found. There are quantitative differences in the sources of projections to the nodulus, the ventral uvula and the flocculus, all of which belong to the vestibulocerebellum. The largest sources for projections to the nodulus and the ventral uvula are from the vestibular nuclei. Among the vestibular nuclei, group-x provides the major projections to the ventral uvula. For the flocculus, in contrast, the major sources of input are the reticular formation and raphe nuclei. These quantitative differences may play an important role for differential functions of the nodulus, the ventral uvula and the flocculus.