Cerebellar efferents in the lizard Varanus exanthematicus. II. Projections of the cerebellar nuclei

The projections of the cerebellar nuclei have been studied in the lizard Varanus exanthematicus with various experimental anatomical techniques. In anterograde degeneration experiments (lesions of the cerebellar peduncle) both ascending and decending contralateral projections were found. Ascending fibers which could be traced from the cerebellar commissure ventralward decussated at the level of the trochlear and oculomotor nuclei. These fibers coursed rostralward to the mesodiencephalic junction. With anterograde tracing techniques (3H-leucine and HRP) this tract was found to terminate in the nucleus ruber and the interstitial nucleus of the fasciculus longitudinalis medialis. Moreover, retrograde tracer studies (HRP, "Fast Blue") showed that this tract appeared to arise mainly in the lateral cerebellar nucleus. With both anterograde degeneration and tracing techniques (3H-leucine and HRP) a bundle of fibers could be followed, which decussates in the basal part of the cerebellum and passes dorsally around the contralateral medial cerebellar nucleus to the lateral side of the brainstem. This contralaterally descending projection system was found, lateral to the vestibular nuclear complex, and as far caudally as the descending vestibular nucleus, to terminate on various vestibular nuclei. Horseradish peroxidase studies showed that this contralaterally descending projection system originates mainly in the medial cerebellar nucleus, but ipsilaterally descending projections were also found. With the fluorescent double labeling technique ("Fast Blue" and "Nuclear Yellow") the projections of the cerebellar nuclei described above were confirmed. Furthermore, double labeling revealed neurons in both cerebellar nuclei (especially the medial nucleus) that project to both the mesencephalon and the cervical spinal cord. The present results indicate that the efferent connections of the cerebellar nuclei in the lizard Varanus exanthematicus are organized as two main projections, an ascending projection comparable to the mammalian brachium conjunctivum arising in the lateral cerebellar nucleus, and a descending projection comparable to the mammalian hook bundle (fasciculus uncinatus), originating mainly in the medial cerebellar nucleus. Such projections are common for terrestrial vertebrates.     

On the projections from the vestibular and perihypoglossal nuclei to the spinal trigeminal and lateral reticular nuclei in the cat

The projection from the vestibular and perihypoglossal nuclei to the spinal trigeminal and lateral reticular nuclei has been studied in cats where the wheat germ agglutinin-horseradish peroxidase complex has been used as a retrograde tracer. All injections were made at the level of the caudal pole of the inferior olive. The medial and descending vestibular, and the perihypoglossal nuclei were found to project to the spinal trigeminal nucleus. The projection to the lateral reticular nucleus reaches its medial-most part only, and originates in the lateral vestibular nucleus. The lateral part of the reticular formation also appears to be the target for some vestibular efferent fibres, mainly from the descending vestibular nucleus. The retrogradely labelled cells within the medial and descending vestibular nuclei are of all sizes and distributed throughout their entire territory. Certain observations furthermore indicate that the fibres reaching the lateral reticular nucleus are collaterals only from the vestibulospinal tract. The projections are bilateral. The observations confirm and extend previous observations on the afferent projections to the spinal trigeminal and lateral reticular nuclei.     

Projections of the vestibular and cerebellar nuclei in Rana pipiens

The efferent projections and cytoarchitecture of the vestibulocerebellar region were examined to determine the nuclear boundaries and potential homologies. The anterior portion of the vestibular complex projects to the ipsilateral oculomotor and trochlear nuclei and is the major source of commissural fibers. Neurons in the rostromedial portions of the complex project to the contralateral trochlear nucleus. Large neurons in the ventrolateral portion of the complex give rise to a bilateral vestibulospinal pathway. Medium-sized neurons in the neuropil and small neurons in the central gray giving rise to bilateral projections to the spinal cord and oculomotor nuclei as well as commissural and ipsilateral cerebellar efferents. Projections from the nucleus of the cerebellum reach the contralateral spinal cord and cerebellar nucleus and there is also a bilateral projection to the ventral rhombencephalic and mesencephalic basal plates. The medial portion of the nucleus gives rise to commissural, ipsilateral mesencephalic and contralateral spinal projections. The lateral portion of the nucleus projects to the contralateral ventral mesencephalon. On the whole, the results of this investigation substantiate the division of the anuran vestibular complex in anurans into nuclei which may be homologous to the superior nucleus and nucleus of Deiters in mammals. The case for distinct descending and medial nuclei is less compelling. Further, it appears possible to divide the nucleus of the cerebellum into medial and lateral components whose connectivity is similar to that of reptiles and to a lesser extent mammals.     

A quantitative study of the vestibular commissures in the gerbil

Direct commissural connections between the bilateral vestibular nuclear complexes (VNC) were investigated in the gerbil using ionophoretic injections of horseradish peroxidase into individual vestibular nuclei. Labelled commissural neurons were counted, the cell counts adjusted by the relative nuclear volume, and the results treated quantitatively. The medial nucleus (MVN) contained the greatest number of commissural neurons. The MVN projected to each of the contralateral vestibular nuclei, but most strongly to the contralateral MVN and superior (SVN) nucleus. The SVN projected modestly to the contralateral VNC. Commissural connections of the descending nucleus were weak. Commissural afferents to the MVN were topographically organized. The crossed fastigiovestibular projection was also investigated.     

Connections of the Lateral Reticular Nucleus to the Lateral Vestibular Nucleus in the Rat. An Anterograde Tracing Study with Phaseolus vulgaris Leucoagglutinin

Efferent projections from the lateral reticular nucleus in the rat were investigated with anterograde transport of Phaseolus vulgaris leucoagglutinin. Besides the well known mossy fibre connections to the cerebellar cortex and collaterals to the cerebellar nuclei, a substantial bilateral projection to the lateral vestibular nucleus was found. Terminal arborizations found within this nucleus appeared to detach from the reticulocerebellar fibres in the cerebellar white matter and enter the lateral vestibular nucleus from dorsally. This projection may have functional relevance for the control, by ascending spinal pathways, of the descending lateral vestibulospinal tract.     

The spatial organization of the vestibulospinal neurons in the guinea pig]

Quantitative investigation of the spatial organization of vestibulospinal neurons has been performed on a guinea pig using the horseradish peroxidase retrograde transport method. After unilateral injection in the upper cervical and low thoracic spinal cord the labelled neurons were found unilaterally in the lateral vestibular nucleus and bilaterally in descending and medial vestibular nuclei. Distribution of vestibulospinal neurons within the brainstem has been analyzed. It was revealed that projections of some neurons of medial and descending vestibular nuclei coincided with spinal projections of cortical and rubral descending pathways. Functional significance of the vestibulospinal system in the supraspinal motor control was discussed.     

Development of the vestibular apparatus and central vestibular connections in a wallaby (Macropus eugenii)

We have studied the early development of the vestibular apparatus and its central connections in the tammar wallaby (Macropus eugenii) in order to determine whether the vestibular system anatomy is sufficiently mature at birth to assist in climbing to the pouch. Structural development was studied with the aid of hematoxylin and eosin stained sections and immunoreactivity for GAP-43, whereas the development of vestibular system connections was examined by carbocyanine dye tracing. At the time of birth, the otocyst has distinct utricle, saccule and semicircular canals with immature sensory regions receiving innervation by GAP-43 immunoreactive fibers. Vestibular nerve fibers can be traced into the brainstem to the developing vestibular nuclei, which are not yet cytoarchitectonically distinct. The vestibular nuclei do not contribute direct projections to the lower cervical spinal cord at birth; most bulbospinal projections in the newborn appear to be derived bilaterally from the gigantocellular, lateral paragigantocellular reticular and ventral medullary nuclei. A substantial bilateral projection to the vestibular ganglion and apparatus from the region of the gigantocellular and lateral paragigantocellular nuclei was seen at birth, but not in subsequent ages. This is similar to a projection seen in newborn Ameridelphians. By postnatal day (P) 5, the vestibular apparatus had extensive projections to all vestibular nuclei and neurons projecting in the lateral vestibulospinal tract could be identified in the lateral vestibular nucleus. Cytoarchitectonic differentiation of the vestibular nuclei proceeded over the next 3 to 4 weeks with the emergence of discrete parvicellular and magnocellular components of the medial vestibular nucleus by P19. GAP-43 immunoreactivity stayed high in the lateral vestibulospinal tract for several months after birth, suggesting that the development of this tract followed a prolonged timecourse. Our findings indicate that central and peripheral connections of the vestibular ganglion are present at birth, but that there is no direct projection from the vestibular nuclei to the cervical spinal cord until P5. Nevertheless, the possibility remains that an indirect projection between the vestibular nuclei and the medial reticular formation is present at birth and mediates control of the climb.     

The vestibular complex of the American opossum didelphis virginiana. II. Afferent and efferent connections.

We have demonstrated the connectivity of the opossum's vestibular nuclei using degeneration, autoradiographic and horseradish peroxidase techniques and have found it to be generally comparable to that reported for the cat. Apart from the primary input described in Part I of our study, the cerebellum provides the major source of afferent connections to the vestibular complex. Axons from the cerebellar cortex distribute mainly to vestibular areas which receive no primary afferent projections, e.g., the dorsal part of the lateral vestibular nucleus, the dorsolateral margin of the inferior vestibular nucleus as well as cell groups comparable to "f" and "x." In contrast, fastigial fibers show considerable overlap with primary vestibular input, particularly in the ventral part of the lateral nucleus, the central part of the inferior nucleus and the medial nucleus. Axons of fastigial origin also distribute to the superior vestibular nucleus, to subnuclei "f" and "x" and to the parasolitary region. Although spinal fibers are diffuse within the main vestibular nuclei, they ramify quite densely within subnucleus "x." Most of the spinovestibular projection appears to arise in the cervical spinal cord of the opossum. Ipsilateral connections from the interstitial nucleus of Cajal and surrounding areas end predominantly, but not exclusively, in the medial vestibular nucleus. A crossed midbrain projection has been verified from the red nucleus to cell group "x" and the lateral part of the inferior nucleus, as well as to an area possibly comparable to cell group "z," as described for the cat. In Part I of our study we have shown that the major targets of primary vestibular fibers are the central part of the superior nucleus, a portion of the parabrachial complex possibly comparable to subnucleus "y"," the ventral part of the lateral nucleus and the medial nucleus. All of these primary zones give rise to fibers supplying extraocular nuclei and surrounding areas (present study). The ascending midbrain fibers from the superior nucleus end mainly ipsilaterally, whereas those from the putative subnucleus "y" and the medial vestibular nucleus distribute contralaterally for the most part. Although the dorsal part of the lateral vestibular nucleus has no primary vestibular input, it does receive a major projection from the cerebellar cortex. This same region of the lateral nucleus projects to the spinal cord, but not to extraocular nuclei. The ventral part of the lateral nucleus, and perhaps the medial nucleus, also relay to the spinal cord. Additional projections from all vestibular nuclei to the reticular formation provide indirect routes through which the vestibular nuclei can potentially effect multiple systems, including those innervating the spinal cord. Finally, commissural vestibular connections of the opossum are shown to arise within all four major nuclei.     

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 the cerebellum in the pigeon (Columba livia): III. Corticovestibular connections with eye and neck premotor areas.

The connections of the cerebellar cortex with vestibular premotor neurons of the oculomotor and collimotor systems in the pigeon were delineated in experiments using WGA-HRP as an anterograde and retrograde tracer. Putative premotor neuron pools were identified by injections into the oculomotor (mIII) and trochlear nuclei (mIV) and into the most rostral portion of the cervical neck motor nucleus, nucleus supraspinalis (SSp). The retrograde data indicate that ipsilateral projections upon oculomotor neurons arise from the medial portions of the superior (VeS) and tangential (Ta) nuclei. Contralateral projections originate from the infracerebellar nucleus, the interstitial vestibular region including the main (lateral) portion of the tangential nucleus, and from the descending and medial vestibular nuclei (VeD, VeM). These projections were confirmed in anterograde studies that also defined the connections of these vestibular premotor regions with specific subnuclear divisions of the pigeon's "oculomotor" nuclei (mIII, mIV, mVI). The organization of projections from the vestibular nuclei to the pigeon's extraocular motoneurons is similar to that reported in mammals. Projections upon neck premotor neurons arise primarily from neurons in the interstitial region of the vestibular nuclear complex. After injections in SSp, retrogradely labeled neurons were found, contralaterally, in the lateral part of the tangential and superior vestibular nuclei and in the dorsolateral vestibular nucleus (VDL). Ipsilateral labeling was seen in the medial interstitial region (VeM, VeD, and medial Ta). These projections were confirmed in anterograde experiments. With the exception of VDL, vestibular nuclei projecting to neck motoneurons also project to extraocular motoneurons. Thus the infracerebellar nucleus projects exclusively, and the superior vestibular nucleus predominantly, upon oculomotor (mIII, mIV) nuclei; VDL projects predominantly upon the neck motor nucleus, whereas the interstitial vestibular regions (medial Ta, rostral VeD, intermediate VeM) project upon both collimotor and oculomotor neurons. The pattern of retrograde labeling seen in the cerebellar cortex after injections into vestibular premotor nuclei was used to define the projections of specific cerebellar cortical zones upon vestibular eye and neck premotor neurons. Corticovestibular projections upon these regions arise from the auricle and lateral unfoliated cortex, the posterior lobe components of cortical zones B and E, and from the vestibulocerebellum. Each of these cortical zones projects upon components of the vestibular nuclear complex, which are premotor to either oculomotor nuclei or collimotor nuclei. The hodological findings are related to the functional organization of the oculomotor and collimotor systems in the pigeon and compared with the mammalian data.     

Projections of the lateral terminal accessory optic nucleus of the common marmoset (Callithrix jacchus)

The connections of the lateral terminal nucleus (LTN) of the accessory optic system (AOS) of the marmoset monkey were studied with anterograde ³H-amino acid light autoradiography and horseradish peroxidase retrograde labeling techniques. Results show a first and largest LTN projection to the pretectal and AOS nuclei including the ipsilateral nucleus of the optic tract, dorsal terminal nucleus, and interstitial nucleus of the superior fasciculus (posterior fibers); smaller contralateral projections are to the olivary pretectal nucleus, dorsal terminal nucleus, and LTN. A second, mejor bundle produces moderate-to-heavy labeling in all ipsilateral, accessory oculornotor nuclei (nucleus of posterior commissure, interstitial nucleus of Cajal, nucleus of Darkschewitsch) and nucleus of Bechterew; some of the fibers are distributed above the caudal oculomotor complex within the supraoculornotor periaqueductal gray. A third projection is ipsilateral to the pontine and mesencephalic reticular formations, nucleus reticularis tegmenti pontis and basilar pontine complex (dorsolateral nucleus only), dorsal parts of the medial terminal accessory optic nucleus, ventral tegmental area of Tsai, and rostral interstitial nucleus of the medial longitudinal fasciculus. Lastly, there are two long descending bundles: (1) one travels within the medial longitudinal fasciculus to terminate in the dorsal cap (ipsilateral > > contralateral) and medial accessory olive (ipsilateral only) of the inferior olivary complex. (2) The second soon splits, sending axons within the ipsilateral and contralateral brachium conjunctivum and is distributed to the superior and medial vestibular nuclei. The present findings are in general agreement with the documented connections of LTN with brainstem oculomotor centers in other species. In addition, there are unique connections in marmoset monkey that may have developed to serve the more complex oculomotor behavior of nonhuman primates. © 1995 Wiley-Liss, Inc.     

The vestibulothalamic connections in the rat: A morphological analysis using wheat germ agglutinin-horseradish peroxidase

The vestibulothalamic connections were studied in the rat using wheat germ agglutinin-horseradish peroxidase (WGA-HRP). The distributions of anterograde labelling of fibers and terminals in the brainstem and the thalamus were analyzed by injecting WGA-HRP into the superior (SVN) and lateral (LVN) vestibular nuclei, and the medial (MVN) and inferior (IVN) vestibular nuclei. The distributions of retrograde labelling of cells were analyzed in the vestibular nuclear complex by injecting WGA-HRP into the thalamus centered in the central lateral nucleus (CL), ventral posterolateral nucleus (VPL), and rostral part of the dorsal medial geniculate nucleus (rMGd). The vestibular projection to the CL via the medial longitudinal fasciculus (MLF) and the ascending tract of Deiters (ATD) originates mainly in the contralateral MVN and ipsilateral SVN. The vestibular projections to the VPL and the ventral lateral nucleus (VL) via MLF, ATD and superior cerebellar peduncle (SCP) originate mainly in the MVN and SVN, bilaterally. The projection to the rMGd via the lateral lemniscus-inferior collicular brachium, and MLF (and SCP) originates in the contralateral IVN.     

Spinovestibular projections in the rat,with particular reference to projections from the central cervical nucleus to the lateral vestibular nucleus

Projections from the spinal cord to the vestibular nuclei were examined following injections of Phaseolus vulgaris–leucoagglutinin, cholera toxin subunit B, or biotinylated dextran at various levels of the spinal cord in the rat. Labeled terminals were abundant after injections of the tracers into the C2 and C3 segments containing the central cervical nucleus. Labeled terminals were seen in the descending vestibular nucleus and the parvocellular, magnocellular, and caudal parts of the medial vestibular nucleus throughout its rostrocaudal extent. Labeled terminals were most numerous in the lateral vestibular nucleus throughout its rostrocaudal extent. The projections from the central cervical nucleus to the vestibular nuclei were exclusively contralateral to the cells of origin because the axons of the central cervical nucleus neurons cross in the spinal cord. Following tracer injections in the cervical enlargement, many labeled terminals were seen in the magnocellular part of the medial vestibular nucleus, but a few were seen in the lateral and the descending vestibular nucleus. Injections into more caudal segments resulted in sporadic terminal labeling in the magnocellular part of the medial vestibular nucleus, the descending vestibular nucleus, and the caudal part of the lateral vestibular nucleus. The results indicate that primary neck afferent input relayed at the central cervical nucleus is mediated directly to the contralateral vestibular nuclei. It is suggested that this projection serves as an important linkage from the upper cervical segments to the lateral vestibulospinal tract in the tonic neck reflex. © 1995 Wiley-Liss, Inc.     

Descending supraspinal pathways in amphibians: III. Development of descending projections to the spinal cord in Xenopus laevis with emphasis on the catecholaminergic inputs

In developmental stages of the clawed toad, Xenopus laevis, we describe the ontogeny of descending supraspinal connections, catecholaminergic projections in particular, by means of retrograde tracing techniques with dextran amines. Already at embryonic stages (stage 40), spinal projections from the reticular formation, raphe nuclei, Mauthner neurons, vestibular nuclei, the locus coeruleus, the interstitial nucleus of the medial longitudinal fasciculus, the posterior tubercle, and the periventricular nucleus of the zona incerta are well developed. At the beginning of the premetamorphic period (stage 46), spinal projections arise from the suprachiasmatic nucleus, the torus semicircularis, the pretectal region, and the ventral telencephalon. After stage 48, tectospinal and cerebellospinal projections develop, with spinal projections from the preoptic area following at stage 51. Rubrospinal projections are present at stage 50. During the prometamorphic period, spinal projections arise in the nucleus of the solitary tract, the lateral line nucleus, and the mesencephalic trigeminal nucleus. With in vitro double-labeling methods, based on retrograde tracing of dextran amines in combination with tyrosine hydroxylase (TH) immunohistochemistry, we show that at stage 40/41, catecholaminergic (CA) neurons in the posterior tubercle are the first to project to the spinal cord. Subsequently, at stage 43, new projections arise in the periventricular nucleus of the zona incerta and the locus coeruleus. The last CA projection to the spinal cord originates from neurons in the nucleus of the solitary tract at the beginning of prometamorphosis (stage 53). Our data show a temporal, rostrocaudal sequence in the development of the CA cell groups projecting to the spinal cord. Moreover, the early appearance of CA fibers, preterminals and terminal-like structures in dorsal, intermediate, and ventral zones of the embryonic spinal cord, suggests an important role for catecholamines during development in nociception, autonomic functions, and motor control at the spinal level.     

Fastigial efferent projections in the monkey: an autoradiographic study.

Because fastigial efferent fibers partially decussate within the cerebellum and cerebellar corticovestibular projections pass near, or through, the fastigial nucleus (FN), degeneration studies based on lesions in the nucleus leave unresolved questions concerning fastigial projections. Attempts were made to determine fastigial projections in the monkey using autoradiographic tracing technics. Cells in rostral, caudal and all parts of the FN were labeled with [³H] amino acids. Selective labeling of neurons in either rostral or caudal parts of the FN results in transport of isotope primarily via fibers of the contralateral uncinate fasciculus (UF) and the ipsilateral juxtarestiform body (JRB). Fastigial projections to the vestibular nuclei are mainly to ventral portions of the lateral (LVN) and inferior (IVN) vestibular nuclei, are nearly symmetrical and are quantitatively similar on each side. Fastigiovestibular projections to cell groups f and x arise from all parts of the FN and are mainly crossed; modest projections to the medial vestibular nucleus are uncrossed. No fastigial efferent fibers end in the superior vestibular nucleus on either side, or in dorsal regions of the LVN. Crossed fibers descending in IVN terminate in the nucleus parasolitarius. Fastigioreticular fibers arise predominately from rostral regions of the FN, are entirely crossed and project mainly to: (1) medial regions of the nucleus reticularis gigantocellularis, (2) the dorsal paramedian reticular nucleus and (3) the magnocellular part of the lateral reticular nucleus. Fastigiopontine fibers, emerge with the UF, bypass the vestibular nuclei and terminate upon the contralateral dorsolateral pontine nuclei. Crossed fastigiospinal fibers separate from fastigiopontine fibers and descend in the ventrolateral tegmentum beneath the spinal trigeminal tract; in the medulla and upper cervical spinal cord these fibers are intermingled with those of the vestibulospinal tract. Fastigiospinal fibers terminate in the anterior gray horn at C-1 and probably descend further. Ascending fastigial projections arise from caudal parts of the FN, are entirely crossed and ascend in dorsal parts of the midbrain tegmentum. Label is transported bilaterally to the superior colliculi and the nuclei of the posterior commissure. Contralateral fastigiothalamic projections terminate in the ventral posterolateral (VPLc and VPLo) and in parts of the ventral lateral (VLo) thalamic nuclei. The major region of termination of fastigiothalamic fibers is in VPLo. Fastigiothalamic projections, probably conveying impulses concerned with equilibrium and somatic proprioception, appear to impinge upon thalamic neurons receiving inputs from less specialized receptors that signal information concerning position sense and body movement. More modest fastigial projections to VLo could directly influence activity of neurons in the primary motor cortex.     

Central distribution of cervical primary afferents in the rat, with emphasis on proprioceptive projections to vestibular, perihypoglossal, and upper thoracic spinal nuclei

The projections of primary afferents from rostral cervical segments to the brainstem and the spinal cord of the rat were investigated by using anterograde and transganglionic transport techniques. Projections from whole spinal ganglia were compared with those from single nerves carrying only exteroceptive or proprioceptive fibers. Injections of horseradish peroxidase (HRP) or wheat germ agglutinin-horseradish peroxidase conjugate (WGA-HRP) were performed into dorsal root ganglia C2, C3, and C4. Free HRP was applied to the cut dorsal rami C2 and C3, greater occipital nerve, sternomastoid nerve, and to the C1/2 anastomosis, which contains afferents from suboccipital muscles and the atlanto-occipital joint. WGA-HRP injections into ganglia C7 and L5 were performed for comparative purposes. Injections of WGA-HRP or free HRP into rostral cervical dorsal root ganglia and HRP application to C2 and C3 dorsal rami produced labeling in dorsal and ventral horns at the level of entrance, the central cervical nucleus, and in external and main cuneate nuclei. From axons ascending to pontine and descending to upper thoracic spinal levels, medial collaterals were distributed to medial and descending vestibular, perihypoglossal and solitary nuclei, and the intermediate zone and Clarke's nucleus dorsalis in the spinal cord. Lateral collaterals projected mainly to the trigeminal subnucleus interpolaris and to lateral spinal laminae IV and V. Results from HRP application to single peripheral nerves indicated that medial collaterals were almost exclusively proprioceptive, whereas lateral collaterals were largely exteroceptive with a contribution from suboccipital proprioceptive fibers. WGA-HRP injections into dorsal root ganglia C7 and L5 failed to produce significant labeling within vestibular and periphypoglossal nuclei, although they demonstrated classical projection sites within the brainstem and spinal cord. The consistent collateralisation pattern of rostral cervical afferents along their whole rostrocaudal course enables them to contact a variety of precerebellar, vestibulospinal, and preoculomotor neurons. These connections reflect the well-known significance of proprioceptive neck afferents for the control of posture, head position, and eye movements.     

Afferent and efferent connections of the medial, inferior and lateral vestibular nuclei in the cat and monkey

Attempts were made to determine the afferent and efferent connections of the medial (MVN), inferior (IVN) and lateral (LVN) vestibular nuclei (VN) in the cat and monkey using retrograde and anterograde axoplasmic transport technics. Injections of HRP and [3H]amino acids were made selectively into MVN, IVN and LVN and into: (1) MVN and IVN, (2) LVN and IVN and (3) all 4 VN. Contralateral afferents to MVN arise from (1) the nuclei prepositus (NPP) and intercalatus (NIC), (2) all parts of MVN and cell group 'y' and (3) parts of the superior vestibular nucleus (SVN), IVN and the fastigial nucleus (FN). Ipsilateral projections to MVN arise from: (1) a central band of the flocculus and the nodulus and uvula, (2) the interstitial nucleus of Cajal (INC), and (3) visceral nuclei of the oculomotor nuclear complex (OMC). Efferent projections of MVN are to: (1) the ipsilateral supraspinal nucleus (SSN), and (2) the contralateral central cervical nucleus (CCN), MVN, SVN, cell group 'y', the rostroventral region of LVN, the trochlear nucleus (TN) and the INC. Projections to the abducens nuclei (AN) and the OMC are bilateral. Some ascending fibers in the cat cross within the OMC. In the monkey fibers from MVN end in a central band of the ipsilateral flocculus. Afferents to IVN arise ipsilaterally from SVN, the nodulus, the uvula and the anterior lobe vermis. Contralateral afferents arise from: (1) parts of CCN, MVN, SVN, IVN and cell group 'y' and (2) the central third of the FN. IVN receives bilateral projections from the perihypoglossal nuclei (PH) and the visceral nuclei of the OMC. Efferents from IVN project: (1) ipsilaterally to nucleus beta of the inferior olive, (2) contralaterally to parts of MVN, SVN and cell group 'y' and (3) bilaterally to the paramedian reticular nuclei. No commissural fibers interconnect cell groups 'f' and 'x'. Ascending fibers from IVN terminate contralaterally in the TN and the OMC. In the monkey fibers from IVN terminate in the ipsilateral nodulus, uvula and anterior lobe vermis; no fibers project to FN in either the cat or the monkey. Afferents to the LVN arise primarily from the ipsilateral anterior lobe vermis and bilaterally from rostral parts of the FN. No commissural fibers interconnect the LVN. Projections of the LVN are primarily to spinal cord via the vestibulospinal tract (VST); collaterals of the VST terminate in the lateral reticular nucleus (LRN). Ascending uncrossed projections from LVN in the cat terminate in the medial rectus subdivision of the OMC.(ABSTRACT TRUNCATED AT 400 WORDS)