Central projections of the saccular and utricular nerves in macaques

The central projections of the utricular and saccular nerve in macaques were examined using transganglionic labeling of vestibular afferent neurons. In these experiments, biotinylated dextran amine was injected directly into the saccular or utricular neuroepithelium of fascicularis (Macaca fascicularis) or rhesus (Macaca mulatta) monkeys. Two to 5 weeks later, the animals were killed and the peripheral vestibular sensory organs, brainstem, and cerebellum were collected for analysis. The principal brainstem areas of saccular nerve termination were lateral, particularly the spinal vestibular nucleus, the lateral portion of the superior vestibular nucleus, ventral nucleus y, the external cuneate nucleus, and cell group l. The principal cerebellar projection was to the uvula with a less dense projection to the nodulus. Principle brainstem areas of termination of the utricular nerve were the lateral/dorsal medial vestibular nucleus, ventral and lateral portions of the superior vestibular nucleus, and rostral portion of the spinal vestibular nucleus. In the cerebellum, a strong projection was observed to the nodulus and weak projections were present in the flocculus, ventral paraflocculus, bilateral fastigial nuclei, and uvula. Although there is extensive overlap of saccular and utricular projections, saccular inputs to the lateral portions of the vestibular nuclear complex suggest that saccular afferents contribute to the vestibulospinal system. In contrast, the utricular nerve projects more rostrally into areas of known concentration of vestibulo-ocular related cells. Although sparse, the projections of the utricle to the flocculus/ventral paraflocculus suggest a potential convergence with floccular projection inputs from the vestibular brainstem that have been implicated in vestibulo-ocular motor learning.     

Projection of reconstructed single purkinje cell axons in relation to the cortical and nuclear aldolase C compartments of the rat cerebellum

Although the overall topography of the cerebellar corticonuclear projection formed by Purkinje cell (PC) axons has been described, only a few studies have dealt with the organization of this projection at the level of individual PC axons. Thus, we reconstructed 65 single PC axons that were labeled with biotinylated dextran amine in the rat. We then analyzed the relationship between the projections of these PCs and the compartmentalization of the cerebellar cortex and nuclei based on the topography of olivocerebellar projection and aldolase C expression in PCs. After giving rise to short local recurrent collaterals near the soma, a PC axon formed a terminal arbor in a specific small area in the cerebellar nuclei (CN). The terminal arbors of vermal PCs were spread more widely than those of hemispheric PCs and sometimes extended to extracerebellar targets. PCs located in any of the aldolase C‐positive (Groups I and II) and ‐negative (Groups III and IV) stripes consistently projected to the caudoventral and rostrodorsal parts of the CN, respectively, precisely in accordance with the compartmentalization of the cortex and nuclei. Mediolateral segregation and rostrocaudal convergence were seen between projections of separate PCs in a single aldolase C compartment. The results revealed a tight link between the projection patterns of individual PC axons, the topography of the olivocerebellar pathway, and the aldolase C expression pattern. Their overall correspondence seems to reflect a basic aspect of cerebellar organization, although some area‐dependent variation in the relationship of these three entities was also present. J. Comp. Neurol. 512:282–304, 2009. © 2008 Wiley‐Liss, Inc.     

Divergent projections of single pontocerebellar axons to multiple cerebellar lobules in the mouse

The basilar pontine nucleus (PN) is the key relay point for the cerebrocerebellar link. However, the projection pattern of pontocerebellar mossy fiber axons, which is essential in determining the functional organization of the cerebellar cortex, has not been fully clarified. We reconstructed the entire trajectory of 25 single pontocerebellar mossy fiber axons labeled by localized injection of biotinylated dextran amine into various locations in the PN and mapped all their terminals in an unfolded scheme of the cerebellum in 10 mice. The majority of axons (20/25 axons) entered the cerebellum through the middle cerebellar peduncle contralateral to the origin, while others entered through the ipsilateral pathway. A small number of axons (1/25 axons) had collaterals terminating in the cerebellar nuclei. Axons projected mostly to a combination of lobules, often bilaterally, and terminated in multiple zebrin (aldolase C) stripes, more frequently in zebrin-positive stripes (83.9%) than in zebrin-negative stripes, with 66.5 mossy fiber terminals on the average. Axons originating from the rostral (plus medial and lateral), central and caudal PN mainly terminated in the paraflocculus, crus I and lobule VIb–c, in the simplex lobule, crus II and paramedian lobule, and in lobules II–VIa, VIII and copula pyramidis, respectively. The results suggest that the interlobular branching pattern of pontocerebellar axons determines the group of cerebellar lobules that are involved in a related functional localization of the cerebellum. In the hemisphere, crus I may be functionally distinct from neighboring lobules (simple lobule and crus II) in the mouse cerebellum based on the pontocerebellar axonal projection pattern.     

Cerebellar, medullary and spinal afferent connections of the paramedian reticular nucleus in the cat

The topographic organization of afferent projections from the deep cerebellar nuclei, medulla oblongata and spinal cord to the paramedian reticular nucleus (PRN) of the cat was studied using the horseradish peroxidase (HRP) method of retrograde labelling. Discrete placements of HRP within each of the dorsal (dPRN) and ventral (vPRN) regions of the PRN showed some segregation of input. The deep cerebellar nuclei project in a predominantly contralateral fashion upon the PRN. A small but significant ipsilateral fastigial afferent component is also present. The fastigial and dentate nuclei contribute the majority of fibers to the dPRN whereas the interposed nucleus provides very little. The vPRN receives a relatively uniform input from all 3 cerebellar nuclei. Both lateral vestibular nuclei contribute the majority of fibers from the vestibular nuclear complex largely from their dorsal division. Additional input arises from bilateral medial and inferior vestibular nuclei. The vPRN receives relatively more fibers from the inferior vestibular nuclei than does the dPRN while inputs from the medial vestibular nuclei are comparably sparse. The PRN receives bilateral projections from the nucleus intercalatus (of Staderini). A significant projection to the contralateral PRN occurs from the ventrolateral subnucleus of the solitary complex and its immediate vicinity. Additional sources of medullary afferent input include the lateral, gigantocellular and magnocellular tegmental fields, the contralateral PRN and the raphe nuclei. Sites of origin of spinal afferents to the dPRN are bilaterally distributed mainly within Rexed's laminae VII and VIII of the cervical cord whereas those to the vPRN are confined largely to the medial portion of the contralateral lamina VI in the C1 segment. A few labelled cells are found in the thoracolumbar cord with those to the vPRN being more caudal. These data provide the neuroanatomical substrate for a better understanding of the functional role of the PRN in mediating cardiovascular responses appropriate to postural changes.     

Organization of the inferior colliculus of the gerbil (Meriones unguiculatus): differences in distribution of projections from the cochlear nuclei and the superior olivary complex

The inferior colliculus (IC) receives its major ascending input from the cochlear nuclei, the superior olivary complex, and the nuclei of the lateral lemniscus. To understand better the terminal distribution of the inputs from these sources relative to one another, we made focal injections of a retrograde tracer, biotinylated dextran amine, in different parts of the IC in 74 gerbils (Meriones unguiculatus). The cases could be divided into three groups based on counts of labeled cells in brainstem auditory nuclei. Group 1 cases had labeled cells in both the cochlear nuclei and the lateral and medial superior olivary nuclei. Group 2 cases had labeled cells in the cochlear nuclei but few or none in the lateral and medial superior olivary nuclei. Both groups had labeled cells in the nuclei of the lateral lemniscus and the superior paraolivary nucleus. Group 3 cases had few labeled cells in any of the ascending auditory pathways. The group to which a case belonged was strongly related to the location of the injection site in the IC. The injection sites for both group 1 and group 2 were located in the central nucleus, but those for group 1 tended to be located laterally relative to those for group 2, which were located more medially and caudally. The injection sites for group 3 cases lay outside the central nucleus of the IC. The two regions of the central nucleus of the IC, distinguished on the basis of connectivity, are likely to subserve different functions.     

Single axonal morphology and termination to cerebellar aldolase C stripes characterize distinct spinocerebellar projection systems originating from the thoracic spinal cord in the mouse

The spinocerebellar projection has an essential role in sensorimotor coordination of limbs and the trunk. Multiple groups of spinocerebellar projections have been identified in retrograde labeling studies. In this study, we aimed at characterizing projection patterns of these groups using a combination of anterograde labeling of the thoracic spinal cord and aldolase C immunostaining of longitudinal stripes of the cerebellar cortex in the mouse. We reconstructed 22 single spinocerebellar axons, wholly in the cerebellum and brain stem and partly, in the spinal cord. They were classified into three groups, (a) non‐crossed axons of Clarke's column neurons (NCC, 8 axons), (b) non‐crossed axons of marginal Clarke's column neurons (NMCC, 7 axons), and (c) crossed axons of neurons in the medial ventral horn (CMVH, 7 axons), based on previous retrograde labeling studies. While NCC axons projected mainly to multiple bilateral stripes in vermal lobules II–IV and VIII–IX, and the ipsilateral medial cerebellar nucleus, NMCC axons projected mainly to ipsilateral stripes in paravermal lobules II–V and copula pyramidis, and the anterior interposed nucleus. CMVH axons projected bilaterally to multiple stripes in lobules II–V with a small number of terminals but had abundant collaterals in the spinal cord and medullary reticular nuclei as well as in the vestibular and cerebellar nuclei. The results indicate that, while CMVH axons overlap with propriospinal and spinoreticular projections, NCC and NMCC axons are primarily spinocerebellar axons, which seem to be involved in relatively more proximal and distal sensorimotor controls, respectively.     

Multiple topographically organized projections connect the central nucleus of the inferior colliculus to the ventral division of the medial geniculate nucleus in the gerbil, Meriones unguiculatus

The ventral division of the medial geniculate nucleus (MGv) receives almost all of its ascending input from the ipsilateral central nucleus of the inferior colliculus (CNIC). In a previous study (Cant and Benson [2006] J. Comp. Neurol. 495:511-528), we made injections of biotinylated dextran amine into the CNIC of the gerbil and demonstrated that it can be divided into two parts. One part (zone 1) receives almost all of its ascending input from the cochlear nuclei, the nuclei of the lateral lemniscus, and the main nuclei of the superior olivary complex; the other part (zone 2) receives inputs from the cochlear nuclei and nuclei of the lateral lemniscus but few or no inputs from the main olivary nuclei. Here we show that these two parts of the CNIC project differentially to the MGv. Axons labeled anterogradely by injections in zone 1 project throughout the rostral two-thirds of the MGv, whereas axons from zone 2 project to the caudal third of the MGv. Throughout much of their extent, the terminal fields do not appear to overlap, although both parts of the CNIC project to medial and dorsal parts of the MGv, and there may be overlap in the most ventral part as well. The results indicate that two parallel pathways arising in the CNIC remain largely separate in the medial geniculate nucleus of the gerbil. It seems most likely that the neurons in the two terminal zones in the MGv perform different functions in audition.     

Cerebellar nucleo-cortical neurons projecting to the vermis of lobule VII in the rat

Cerebellar nucleo-cortical neurons projecting to lobule VII vermis in the rat are located in the caudal fastigial nucleus (FN) and in the white matter ventral to the intracerebellar nuclei. The cortico-nuclear and nucleo-cortical projections of lobule VII vermis are only in part reciprocal; nucleo-cortical neurons in the dorsolateral protuberance (dlp) of the FN and ventral to the more lateral cerebellar nuclei, may serve to relate the cerebellar hemispheres to the vermis.     

Central projections of cochlear nerve fibers in the alligator lizard

The auditory (cochlear) ganglion cells of the alligator lizard (Gerrhonotus multicarinatus) give rise to two types of peripheral fibers: tectorial fibers, which contact hair cells covered by a tectorial membrane, and free-standing fibers, which contact hair cells without a tectorial membrane. To determine the central projections of these fibers, we applied intracellular and extracellular injections of horseradish peroxidase (HRP) to the peripheral component of the cochlear nerve. After histological processing with diaminobenzidine, individual cochlear nerve fibers could be traced through serial sections with the aid of a light microscope and drawing tube. The projection patterns formed two morphologically distinct groups. Neurons whose peripheral processes contacted tectorial hair cells in the cochlea projected to three divisions of the cochlear nucleus: nucleus magnocellularis lateralis (NML), nucleus magnocellularis medialis (NMM), and nucleus angularis lateralis (NAL). Neurons whose peripheral processes contacted free-standing hair cells projected primarily to the nucleus angularis medialis (NAM), although some also sent a single, thin branch to the NML; these neurons never projected to NAL or NMM. Morphometric comparisons of tectorial and free-standing fibers demonstrate that tectorial fibers have a larger axonal diameter, form a greater number of terminal swellings, and make proportionally more somatic contacts. By correlating the morphologically defined groups with previously reported physiologically defined groups, we conclude that different divisions of the cochlear nucleus are associated with separate frequency ranges and that stimuli in the different frequency ranges may be processed separately in the brain.     

Central projections of the vestibular nerve: a review and single fiber study in the Mongolian gerbil

The primary purpose of this article is to review the anatomy of central projections of the vestibular nerve in amniotes. We also report primary data regarding the central projections of individual horseradish peroxidase (HRP)-filled afferents innervating the saccular macula, horizontal semicircular canal ampulla, and anterior semicircular canal ampulla of the gerbil.

In total, 52 characterized primary vestibular afferent axons were intraaxonally injected with HRP and traced centrally to terminations. Lateral and anterior canal afferents projected most heavily to the medial and superior vestibular nuclei. Saccular afferents projected strongly to the spinal vestibular nucleus, weakly to other vestibular nuclei, to the interstitial nucleus of the eighth nerve, the cochlear nuclei, the external cuneate nucleus, and nucleus y.

The current findings reinforce the preponderance of literature. The central distribution of vestibular afferents is not homogeneous. We review the distribution of primary afferent terminations described for a variety of mammalian and avian species. The tremendous overlap of the distributions of terminals from the specific vestibular nerve branches with one another and with other sensory inputs provides a rich environment for sensory integration.     

Central projections of lagenar primary neurons in the chick

Perception of linear acceleration and head position is the function of the utricle and saccule in mammals. Nonmammalian vertebrates possess a third otolith endorgan, the macula lagena. Different functions have been ascribed to the lagena in arboreal birds, including hearing, equilibrium, homing behavior, and magnetoreception. However, no conclusive evidence on the function of the lagena in birds is currently available. The present study is aimed at providing a neuroanatomical substrate for the function of the lagena in the chicken as an example of terrestrial birds. The afferents from the lagena of chick embryos (E19) to the brainstem and cerebellum were investigated by the sensitive lipophilic tracer Neuro Vue Red in postfixed ears. The results revealed that all the main vestibular nuclei, including the tangential nucleus, received lagenar projections. No lagenar terminals were found in auditory centers, including the cochlear nuclei. In the cerebellum, the labeled terminals were found variably in all of the cerebellar nuclei. In the cerebellar cortex, the labeled fibers were found mostly in the uvula, with fewer afferents in the flocculus and paraflocculus. None was seen in the nodulus. The absence of lagenar afferent projections in auditory nuclei and the presence of a projection pattern in the vestibular nuclei and cerebellum similar to that of the utricle and saccule suggest that the primary role of the lagena in the chick lies in the processing of vestibular information related to linear acceleration and static head position. J. Comp. Neurol. 521:3524‐3540, 2013. © 2013 Wiley Periodicals, Inc.     

Ascending auditory projections to the inferior colliculus in the adult gerbil, Meriones unguiculatus

Ascending auditory projections to the inferior colliculus (IC) of the adult gerbil were studied using the retrograde transport of horseradish peroxidase. Our results indicate that in gerbils, the IC receives afferent projections from most brainstem auditory nuclei. A strong contralateral projection originates in the cochlear nuclear complex (CN). A smaller but consistent projection from all three divisions of ipsilateral CN is also present. The medial superior olive (MSO), superior parolivary nucleus, and ventral nucleus of the lateral lemniscus all maintain ipsilateral projections to the IC. Bilateral projections arise from the lateral superior olive, lateral nucleus of the trapezoid body, and dorsal nucleus of the lateral lemniscus. Previous investigations in other mammalian species provide conflicting data concerning the magnitude of a direct ipsilateral projection from CN to the IC. Our quantitative data indicate that the ipsilateral projection from CN in the gerbil is nearly one third as large as the projection from ipsilateral MSO. The projection from contralateral CN is six times larger than the MSO projection. The distribution of labeled cells across the rostrocaudal extent of MSO and the three divisions of the cochlear nuclear complex are presented.     

The ventral nucleus of the lateral lemniscus of the gerbil (Meriones unguiculatus): organization of connections with the cochlear nucleus and the inferior colliculus

The spatial organization of projections from the ventral cochlear nucleus (VCN) to the ventral nucleus of the lateral lemniscus (VNLL) and from the VNLL to the central nucleus of the inferior colliculus (CNIC) was investigated by using neuroanatomical tracing methods in the gerbil. In order to label cells in the VNLL that project to the CNIC, focal injections of biotinylated dextran amine (BDA) were made into different CNIC regions. Retrogradely labeled cells were distributed throughout the dorsal-to-ventral axis of the VNLL in all cases. In contrast, the distribution of labeled cells across the lateral-to-medial dimension of the VNLL was related to the location of the injection site along the dorsolateral to ventromedial (frequency) axis of the CNIC. Cells projecting to dorsolateral (low-frequency) regions of the CNIC were located peripherally in the VNLL, mainly laterally and caudally, whereas those projecting to ventromedial (high-frequency) regions of the CNIC tended to be clustered centrally. Projections to the VNLL were labeled anterogradely following injections of BDA in the VCN. The distribution of terminal fields in the VNLL closely paralleled the topographic arrangement of cells projecting to the CNIC; projections from ventrolateral (low-frequency) areas of the VCN terminated mainly along the lateral and caudal borders of the VNLL, whereas projections from dorsomedial (high-frequency) areas terminated in more central regions. The results demonstrate a topographic organization of the major afferent and efferent connections of the gerbil VNLL.     

Primary projections and efferent cells of the VIIIth cranial nerve in the monitor lizard, Varanus exanthematicus

In order to describe the central relations of both the afferent and efferent components of the VIIIth cranial nerve in one reptile, the methods of anterograde and retrograde axonal transport and anterograde degeneration were used to study the vestibular and cochlear projections and the efferent system of this nerve in Varanus exanthematicus. On the basis of cresyl violet and Klüver-Barrera staining, five vestibular nuclei, four cochlear nuclei, and two clusters of small cells which could not be designated as strictly auditory or vestibular are distinguished. The vestibular nuclei include the nucleus dorsolateralis, nucleus ventrolateralis, nucleus tangentialis, nucleus ventromedialis, and nucleus descendens. The well-developed cochlear nuclear complex includes the nucleus angularis, nuclei magnocellulares medialis and lateralis, and nucleus laminaris. The two cell clusters are located dorsolaterally in the brainstem just ventrolateral to the acoustic tubercle. The primary afferent vestibular fibers coursing in the anterior VIIIth nerve root distribute to the ventral portions of all vestibular nuclei except nucleus ventromedialis, whereas the fibers coursing in the posterior root project to the dorsal portions of these nuclei. In nucleus ventromedialis fibers of both roots do not segregate into ventral and dorsal portions. Other targets of the vestibular fibers are the two cell clusters, the granular layer of the ipsilateral cerebellum, the reticular formation, and the descending trigeminal tract and its nucleus. The primary cochlear fibers coursing in the posterior root terminate in nucleus angularis, nuclei magnocellulares medialis and lateralis, and the inner cell strand of nucleus laminaris. The efferent system is, ipsi- and contralaterally in the brainstem, composed of ventral and dorsal cell groups that extend from the level of the principal abducens nucleus caudally where they overlap with the facial motor nucleus. The fibers, which originate from the contralaterally located efferent cells, course beneath the IVth ventricle to exit the brainstem on the ipsilateral side.     

Commissural and ipsilateral internuclear connection of vestibular nuclear complex of the cat

Commissural and ipsilateral intrinsic connections of the vestibular nuclear complex of cats were investigated using retrograde transport of horseradish peroxidase (HRP). HRP was microiontophoretically injected into limited areas (0.2-0.5 mm in diameter) of the respective vestibular nuclei. In the commissural connections, major fibers were observed between the bilateral superior vestibular nuclei (SVN) and between the bilateral descending vestibular nuclei (DVN); a moderate number of fibers was found from the medial vestibular nucleus (MVN) to the contralateral MVN, SVN and lateral vestibular nucleus (LVN) and from the DVN to the contralateral LVN. Minor commissural connections were detected between the bilateral LVN. The ipsilateral internuclear connections of the vestibular nuclear complex were: (1) from the LVN, MVN and DVN to the SVN, (2) from the MVN and DVN to the LVN and (3) from the MVN to the DVN. Minor ipsilateral intrinsic connections were found from the SVN to the MVN.     

Organization of eighth nerve afferent projections from individual endorgans of the inner ear in the teleost, Astronotus ocellatus

Eighth nerve fibers from the saccule, utricle, lagena, and the anterior, horizontal, and posterior semicircular canals of a cichlid fish were traced to the octavolateralis region of the brainstem using HRP and degeneration methods. The anterior, magnocellular, descending, and posterior nuclei of the octavus column receive inputs from all endorgans, whereas the tangential nucleus receives projections only from the utricle and semicircular canals. The most rostral projections only from the utricle and semicircular canals. The most rostral projection from each endorgan is found in the eminentia granularis of the vestibulolateral lobe of the cerebellum. Sparse terminals are found in the medial reticular formation from the utricle adn semicircular canals, and utricular and saccular remain terminate in the vicinity of the lateral dendrite of the Mauthner cell. Utricular and semicircular canal projections consistently overlap centrally as do saccular and lagenar inputs. Afferent fibers from all endorgans end within relatively distinct regions throughout the octavus column of nuclei. Saccular and lagenar inputs lie dorsal to the semicircular canal terminations. Utricular endings are complex, however, in that they overlap dorsally with saccular and lagenar terminals and ventrally with the semicircular canal inputs. Cerebellar inputs are found only in the eminentia granularis of the vestibulolateral lobe, and the densest terminals are from the utricle and the semicircular canals; the sparsest are from the saccule. Previous studies in fish have indicated that generally the utricle and semicircular canals are concerned with he maintenance of static and dynamic equilibrium whereas the saccule and lagena are concerned with auditory reception. There is recent evidence, however, for multiple functions within individual endorgans. Our anatomical findings suggest that in Astronotus each otolithic endorgan carries more than one modality; that the semicircular canals are concerned solely with an equilibrium function; and that acoustic information is processed dorsally and vestibular information ventrally along the octavus column of nuclei. No single nucleus appears to be solely auditory in function and only the tangential nucleus, situated ventrally in the octavus column, appears to be solely vestibular.     

The intrinsic organization of the vestibular complex: evidence for internuclear connevtivity

The HRP anterograde and retrograde labeling techniques provide evidence for extensive internuclear connectivity within the vestibular complex. Specifically: (1) the superior vestibular nucleus is topographically and reciprocally related to the spinal (spv) and medial vestibular nuclei (mv); (2) the lateral vestibular nucleus (lv) is reciprocally related to the mv, and (3) the lv receives afferent fibers from the spv but does not reciprocate this input.     

Dorsal nucleus of the lateral lemniscus in the rat: Concentric organization and tonotopic projection to the inferior colliculus

A basic principle of organization in auditory centers is the topographic-tonotopic order. Whether this applies to the dorsal nucleus of the lateral lemniscus (DNLL), however, is still debated. To clarify this problem, we have utilized the neuroanatomical tracers horseradish peroxidase (HRP) and biotinylated dextran (BD) injected into different regions of the central nucleus of the inferior colliculus (CNIC) in the rat. After large injections of HRP that included most of the CNIC, retrogradely labelled neurons were found all across the ipsi- and contralateral DNLL, showing that all parts of this nucleus innervate the CNIC bilaterally. More neurons were seen consistently on the side contralateral to the injection site. Labelled fibers, however, were abundant ipsilaterally, but scarce in the contralateral DNLL. Single, small injections of HRP or BDinto the CNIC resulted in labelling in restricted areas of the ipsi- and contralateral DNLL. In coronal sections, the neurons and fibers labelled in the ipsilateral DNLL formed a well-defined, ring-shaped structure made of dendrites and axons oriented parallel to each other, which we termed “annular band.” The observation of serial sections revealed that the annular band seen in any individual section represents a slice through a more or less complete three-dimensional, hollow, ovoid structure oriented rostrocau-dally. The position and diameter of the annular band changed as the injection site was shifted along the tonotopic axis of the CNIC. Single injections placed in the ventromedial, high-frequency region of the CNIC produced a large annular band along the periphery of the DNLL. After injections placed in progressively more dorsolateral, lower-frequency regions of the CNIC, the annular band became smaller in diameter and occupied a successively more central position in the DNLL. Double injections along the tonotopic axis of the CNIC resulted in two roughly concentric annular bands. The labelled neurons and fibers in the contralateral DNLL systematically occupied a position symmetric to the annular band seen ipsilaterally. These findings indicate that the rat DNLL is primarily composed of neurons with flattened dendritic arbors and flattened fields of terminal fibers. These two elements intermingle, forming concentric layers around the geometric center of the nucleus. The axons of neurons within corresponding layers on the two sides converge onto the CNIC of both sides in a strict topographic fashion: the peripheral layers project to the ventromedial, high-frequency region of the CNIC, and the central layers project to the dorsolateral, low-frequency region. These results suggest that the concentric arrangement of the DNLL is the substrate of its tonotopic organization. © 1994 Wiley-Liss, Inc.     

Afferent projection from reticular nuclei, inferior olive and cerebellum to lateral vestibular nucleus of the cat as demonstrated by horseradish peroxidase

Afferent connection to lateral vestibular nucleus (LVN) was examined using retrograde transport of horseradish peroxidase (HRP). When HRP was microiontophoretically applied to the immediate vicinity of the LVN neuron, which monosynaptically fired spike upon VIIIth cranial nerve stimulation, HRP-labelled cells were observed in the ipsilateral lateral reticular nucleus, bilateral gigantocellular nucleus, and contralateral dorsal cap and beta-nucleus of inferior olive in addition to various parts of cerebellum.