Cerebellar corticovestibular projections from lobule IX to the descending vestibular nucleus in the cat. A retrograde wheat germ agglutinin-horseradish peroxidase study

Role of the vestibular system in regulating respiratory muscle activity during movement

1. Changes in posture can affect the resting length of the diaphragm, which is corrected through increases in both diaphragm and abdominal muscle activity. Furthermore, postural alterations can diminish airway patency, which must be compensated for through increases in firing of particular upper airway muscles. 2. Recent evidence has shown that the vestibular system participates in adjusting the activity of both upper airway muscles and respiratory pump muscles during movement and changes in body position. 3. Vestibulo-respiratory responses do not appear to be mediated through the brainstem respiratory groups; labyrinthine influences on respiratory pump muscles may be relayed through neurons in the medial medullary reticular formation, which have recently been demonstrated to provide inputs to both abdominal and diaphragm motoneurons. 4. Three regions of the cerebellum that receive vestibular inputs, the fastigial nucleus, the nodulus/uvula and the anterior lobe, also influence respiratory muscle activity, although the physiological role of cerebellar regulation of respiratory activity is yet to be determined. 5. It is practical for the vestibular system to participate in the control of respiration, to provide for rapid adjustments in ventilation such that the oxygen demands of the body are continually matched during movement and exercise.

Role of the inferior olivary complex in motor skills and motor learning in the adult rat

The inferior olivary complex of adult rats was chemically destroyed using intraperitoneal injection of 3-acetylpyridine. Animals were submitted to different motor tasks: hanging test, equilibrium test and motor co-ordination test. The different scores show that 3-acetylpyridine-treated rats had motor co-ordination and static equilibrium deficiencies, whereas their rod suspension capabilities were intact. Animals were also trained on an unrotated rod or on a rod rotating at 5, 10 or 20 r.p.m. 3-Acetylpyridine-treated rats were able to maintain their equilibrium on the unrotated rod and at 5 r.p.m. Moreover, after motor training at 5 r.p.m., rats were able to improve their motor skills and reached the same score as controls. Despite their good motor skills, animals were unable to maintain their equilibrium when rotated at 10 and 20 r.p.m. These results suggest that the inferior olivary complex is needed for motor learning involving the temporal organization of movement.

Synapses from medial olivocochlear branches in the inferior vestibular nucleus

Olivocochlear neurons are auditory efferent neurons that convey information from the brainstem to the auditory periphery. With light and electron microscopy, using mice, we studied the central branches of medial olivocochlear neurons that are given off to the inferior vestibular nucleus. At the level of the electron microscope, the branches form synapses. The synapses are asymmetric with round vesicles, suggesting that they are excitatory. The synapses are formed mainly onto neuronal dendrites. These dendrites have a large range of diameters, and they may emanate from several types of target neurons. These results indicate that the inferior vestibular nucleus is an integrating center for vestibular, auditory, and other types of information, but the results do not fit with current theories about the function of the olivocochlear system.

Secondary vestibulocerebellar mossy fiber projection to the caudal vermis in the rabbit

The vestibulocerebellar projection in the rabbit has been investigated by the anterograde axonal transport of tritiated leucine, wheat germ-agglutinated horseradish peroxidase, and Phaseolus vulgaris leucoagglutinin. Mossy fiber terminals originating from all vestibular nuclei, with the exception of the lateral vestibular nucleus of Deiters, were found bilaterally in the lobules X, IX, and VIII of the caudal vermis, without a clear difference in laterality. Most of the vestibular mossy fiber terminals in the caudal vermis originated in the superior and caudal medial vestibular nuclei. Application of the different tracers led to similar results. The labeled terminals were always most numerous in the lobules X and IXd. Small to moderate numbers of mossy fiber terminals were found in the lobules IXa, b, c, and lobule VIII. The greatest change in the density of terminals occurred in most cases around the apex of lobule IXd and not in the depth of the posterolateral fissure between lobules X and IX. The mossy fiber terminals were not distributed equally over the cortex but showed a preference for the proximal parts of the individual lobules. In all experiments, the terminals exhibited a certain degree of clustering in the mediolateral direction, but the clusters were not arranged in longitudinal zones continuous over successive folia.

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.

Differential mossy fiber projections to the dorsal and ventral uvula in the cat

The brainstem afferents to the uvula were studied by using retrograde axonal transport of horseradish peroxidase in the cat. Findings indicate differential afferent projections to the ventral and dorsal uvula. Major sources projecting to the ventral uvula include the caudal parts of the medial and inferior vestibular nuclei, the x- and f-groups of the vestibular nuclei, the dorsal and central parts of the superior vestibular nucleus, the rostral dorsomedial part of the paramedian nucleus of the pontine nuclei, the caudal part of the prepositus hypoglossal nucleus, and the infratrigeminal nucleus. Labeled cells in the vestibular nuclei were 74.7% of the total number of labeled cells in cat 40. On the other hand, the major sources projecting to the dorsal uvula are the peduncular, paramedian, and lateral nuclei of the pontine nuclei at the rostral and intermediate levels. Labeled cells in the pontine nuclei comprised 82.1% of the total number of labeled cells in cat 1. Findings also indicate that the lateral part of the ventral uvula receives input mainly from the pontine nuclei, whereas the medial part of the ventral uvula receives input mainly from the vestibular nuclei. Mediolateral differences were not found for the dorsal uvula. These mossy fiber zones are mediolaterally wide, with a dorsoventral partition in the uvula, in contrast to the climbing fiber zones, which are narrow (about 0.4 mm) and extend longitudinally throughout the uvula. There are quantitative differences in afferent sources to the ventral uvula and flocculus, both of which belong to the vestibulocerebellum. The largest afferent sources for the ventral uvula are the vestibular nerve and nuclei, whereas the largest sources for the flocculus are the reticular formation and raphe nuclei. These quantitative differences may have an important role for differential functions between the ventral uvula and flocculus. It has been suggested that the ventral uvula controls the velocity storage integrator of the vestibuloocular and optokinetic reflexes, whereas the flocculus is responsible for rapid changes of eye velocity in these reflexes.

Zonal organization of climbing fiber projections to the uvula in the cat

Climbing fiber projections from the inferior olive to the uvula of the cerebellum were studied in the cat by using retrograde axonal transport of horseradish peroxidase. Following large and small injections into various parts of the uvula, the distribution of labeled cells in the inferior olive was investigated. The findings indicate six longitudinal zones extending throughout the dorsal and ventral uvula: the caudal part of the nucleus beta projects to a most medially located zone (caudal beta zone) with a width of about 0.4 mm; the rostral part of the nucleus beta projects to a zone located at about 0.6 mm from the midline (rostral beta zone); the caudal part of the medial accessory olive (MAO) projects to a zone (caudal MAO zone) located lateral to the rostral beta zone; the dorsomedial cell column projects to a zone (dorsomedial cell column zone) located in the intermediate part of the uvula at about 1.2 mm from the lateral edge of the uvula; the ventral lamella of the principal olive (PO) projects to a zone (ventral lamella of PO zone) about 0.7 mm from the lateral edge of the uvula; finally, the rostral part of the MAO projects to the most lateral zone (rostral MAO zone). These conclusions are in general agreement with those of earlier studies and also provide a more detailed zonal configuration of climbing fiber projections to the uvula.

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.

Projection pattern of vestibulocerebellar fibers in the anterior vermis of the cat: an anterograde wheat germ agglutinin-horseradish peroxidase study

The distribution of mossy fiber terminals of vestibulocerebellar fibers was studied in the anterior lobe following a unilateral injection of wheat germ agglutinin-horseradish peroxidase into the medial and descending vestibular nuclei in the cat. In the transverse plane 3 groups of labeled terminals were seen bilaterally: group 1 located in the midline region, group 2 at 0.5 mm, and group 3 between 0.75 and 1.5 mm lateral to the midline. Reconstruction of the distribution in the horizontal plane revealed that the labeled terminals were distributed in 3 areas extending apicobasally in the basal part of the lobules.