Trigeminocerebellar projections to the posterior lobe in the cat, as studied by anterograde transport of wheat germ agglutinin-horseradish peroxidase.

Cerebellar projections of the nucleus interpolaris and oralis of the spinal trigeminal nucleus were studied in the cat by anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP). Injections of WGA-HRP into these nuclei labeled many mossy fiber terminals mainly ipsilaterally in the rostral folium of lobule IX (IXa or IXa + b), the simple lobule, the anterior part (sublobule A) of the paramedian lobule and the posterior part of crus II. Labeled terminals were also seen in the anterior lobe, lobules VI and VII, the anterior part of crus I, and the paraflocculus dorsalis. Projection fields in the horizontal plane of lobules were reconstructed from a series of transverse sections through each folium of lobule IX, the paramedian lobule, and the posterior part of crus II on the ipsilateral side. In sublobule IXa + b, labeled terminals were distributed in five longitudinal areas extending along the apicobasal axis of the sublobule. These five areas were located in the apical two-thirds of the ipsilateral half of the sublobule. Labeled terminals were distributed in five longitudinal areas in sublobule A (the rostral part) of the paramedian lobule. In the posterior part of crus II, four aggregations of labeled terminals were present in cross sections through a lobule. They were distributed in the apicobasal extent of the lobules. The present study indicates that the projection fields of trigeminocerebellar fibers are longitudinally arranged along the apicobasal axis of the cerebellar lobules.     

Single axonal characterization of trigeminocerebellar projection patterns in the mouse

The cerebellar projection from the trigeminal nuclear complex is one of the major populations of the cerebellar inputs. Although this projection is essential in cerebellar functional processing and organization, its morphological organization has not been systematically clarified. The present study addressed this issue by lobule-specific retrograde neuronal labeling and single axonal reconstruction with anterograde labeling. The cerebellar projection arose mainly from the interpolaris subdivision of the spinal trigeminal nucleus (Sp5I) and the principal trigeminal sensory nucleus (Pr5). Although crus II, paramedian lobule, lobule IX, and simple lobule were the major targets, paraflocculus, and other lobules received some projections. Reconstructed single trigeminocerebellar axons showed 77.8 mossy fiber terminals on average often in multiple lobules but no nuclear collaterals. More terminals were located in zebrin-negative or lightly-positive compartments than in zebrin-positive compartments. While Pr5 axons predominantly projected to ipsilateral crus II, Sp5I axons projected either predominantly to crus II and paramedian lobule often bilaterally, or predominantly to lobule IX always ipsilaterally. Lobule IX-predominant-type Sp5I neurons specifically expressed Gpr26. Gpr26-tagged neuronal labeling produced a peculiar mossy fiber distribution, which was dense in the dorsolateral lobule IX and extending transversely to the dorsal median apex in lobule IX. The projection to the cerebellar nuclei was observed in collaterals of ascending Sp5I axons that project to the diencephalon. In sum, multiple populations of trigeminocerebellar projections showed divergent projections to cerebellar lobules. The projection was generally complementary with the pontine projection and partly matched with the reported orofacial receptive field arrangement.     

Projections from the spinal and the principal sensory nuclei of the trigeminal nerve to the cerebellar cortex in the cat, as studied by retrograde transport of horseradish peroxidase.

Projections from the spinal (Vsp) and the principle sensory (Vp) nuclei of the trigeminal nerve to the cerebellar cortex were studied by means of retrograde transport of horseradish peroxidase in the cat. Neurons projecting to the simple lobule and the dorsal part of the paramedian lobule (PMD) were located mainly in the dorsal part of the nucleus interpolaris (Vi) and of the caudal one third of the nucleus oralis (Vo) and in the rostralmost part of the Vo. Neurons projecting to the medial part of the posterior folia of crus II (crus IIp) were located in the dorsal to ventral parts of the Vi and of the caudal one third of the Vo and in the rostralmost part of the Vo, while those projecting to the lateral part of crus IIp were confined to the ventral part of the Vi and of the caudal one third of the Vo. Neurons of the Vp also projected to all of these cortical areas. They were relatively confined to the ventral part of this nucleus. Thest trigeminocerebellar projections were exclusively ipsilateral to the cell origin. There were sparse projections from the Vi and Vo to lobules V to VIIIa. In addition, a small group of neurons in the subnucleus magnocellularis of the nucleus caudalis of the Vsp also projected to the above cortical areas. No projections were, however, observed to the anterior portion of the anterior lobe, crus I, the anterior folia of crus II, paraflocculus, flocculus and the ventral part of the PMD. The majority of these cerebellar projection neurons were medium-sized and triangular, fusiform or ovoid in shape. There were small neurons of similar types and large multipolar neurons as well.     

A re-examination of the cerebellar projections from the gracile, main and external cuneate nuclei in the cat

Cerebellar projections from the dorsal column and external cuneate nuclei in the cat have been studied by means of retrograde axonal transport of horseradish peroxidase. Localized injections covering the entire cerebellar cortex and nuclei show that the gracile nucleus has a weak projection only to the cortex of the anterior lobe, but that there is a conspicuous projection from the main cuneate nucleus to the cerebellum. Most of these fibres reach lobule V and the adjascent parts of lobules IV and VI, and there is also a heavy projection to the paramedian lobule. Some fibres reach lobule IX and possibly also lobules II, III and VIIIB, and nuclear afferents also reach the fastigial and interposite nuclei.Three cerebellar cortical regions are the main targets for the fibres from the external cuneate nucleus, viz. lobule V with the adjacent regions of lobules IV and VI, lobules I and II and lobule IX (the anterior part). Other important afferent regions are the paramedian lobule and the cerebellar nuclei, especially the anterior interposite, and some fibres reach the flocculus.The projections are predominantly ipsilateral.The investigation is the first detailed study of the cerebellar projections from the three nuclei and the findings are discussed in relation to previous experimental observations.     

Cerebellar cortical efferent fibers in the North American opossum,Didelphis virginiana. II. The posterior vermis

The projection pattern of corticonuclear and corticovestibular fibers from vermis lobules VI–X of the North American opossum, Didelphis virginiana, was studied using a modification of the Fink and Heimer (1967) technique. The evidence suggests that corticovestibular projections in opossum are ipsilateral and exit the cerebellum via the juxtarestiform body. Lobules VI and VII contribute few, if any, corticovestibular projections. Corticovestibular fibers from lobule VIII are sparse to moderate and those from lobules IX and X are numerous. The main targets of corticovestibular fibers are the superior and spinal vestibular nuclei with some input to the medial vestibular nucleus, particularly from lobules IX and X. Although degenerated axons course through the lateral vestibular nucleus, they do not appear to terminate therein. Corticonuclear fibers from lobules VI–X are ipsilateral and terminate in the caudal and caudoventral one-third of the medial cerebellar nucleus (NM). Fibers from lateral areas of some vermal lobules appear to enter contiguous parts of the immediately adjacent posterior interposed nucleus. Although each lobule projects into a specific area of caudal and caudoventral NM when the terminal fields for lobules VI–X are superimposed, it is apparent that they are largely coextensive. This is in contrast to the pattern seen in projections from the anterior vermis. The results further indicate that zones A and B are present in lobules VI–X of opossum.     

Distribution of external cuneate nucleus afferents to the cerebellum: I. Notes on the projections from the main cuneate and other adjacent nuclei. An experimental study with radioactive tracers in the cat

Transport of radioactive leucine was used to demonstrate cerebellar projections from the external cuneate nucleus (NCE) and from adjacent portions of the main cuneate nucleus (NC), of the spinal trigeminal nucleus (N.tr.sp.V) and of the vestibular nuclei. Projections from NCE and NC in part terminate over exclusive regions and in part overlap. After injections limited to NCE, labeling is found in all regions of the anterior lobe and lobule VI, in vermal lobules VII, VIII, and IX, and in medial regions of central folia of the paramedian lobule. Afferents from NC are observed in intermediate and lateral regions of lobules IV-VI, in lobules VIII and IX, in medial portions of crura I and II, and in lateral parts of central folia of the paramedian lobule as well as in its rostral folia. Afferents from N.tr.sp.V are distributed in lateral regions of lobules II-VI, in the rostral folium of lobule IX, in medial parts of crura I and II, and in rostral folia of the paramedian lobule. Afferents from the vestibular nuclei are present in vermal lobules VII, IX, and X and in the paramedian lobule. Projections from NCE are bilateral with ipsilateral predominance, whereas those from NC and N.tr.sp.V are ipsilateral. Projections from NCE are generally much denser than those from the other nuclei. Throughout the projection area, afferents from NCE are distributed in greater amounts in folia close to the medullary core and are much less dense near the surface. Afferents from the other nuclei do not show surface-to-depth density differences.     

Olivocerebellar connections in sheep studied with the retrograde transport of horseradish peroxidase

We describe here the morphology of the inferior olive and the localization of labeled cells after HRP injections into various lobules of vermis and hemisphere of the cerebellum of the sheep. The medial part of the caudal half of the medial accessory olive projects to a medial zone in the anterior lobe, the simple lobule, and the lobules VII and VIII. The lateral part of the medial accessory olive projects to more lateral parts of these lobules with the exception of lobule VII. The group beta projects in a differential manner to the lateral parts of the lobules VII and VIII and the medial parts of the lobules IX and X. The dorsomedial cell column projects to lobules VIII, IX, and X; the connections of the dorsal cap are restricted to lobule X. Fibers from the caudal limb of the dorsal accessory olive terminate in the B zone, the simple lobule, and in lobule VIII. The rostral half of the medial accessory olive projects to lobule IX and to the hemisphere. The other projections of the accessory olives and the principal olive to the hemisphere are similar to those reported for the cat. An accessory cell group in the sheep, located between the principal and the dorsal accessory olive, has connections with the caudal vermis and the hemisphere.     

Cerebellar afferents from motor nuclei of cranial nerves, the nucleus of the solitary tract, and nuclei coeruleus and parabrachialis in sheep, demonstrated with retrograde transport of horseradish peroxidase

Following HRP injections in the cerebellar cortex of the sheep (except the ventral part of the anterior lobe, the flocculus and ventral paraflocculus), labeled cells were evident in motor nuclei of cranial nerves (XII, VII, VI, III, visceromotor nucleus of X and nucleus ambiguus), in the solitary tract nucleus, the nucleus coeruleus and the parabrachial nucleus.     

An autoradiographic study of eighth nerve projections in the galah,Eolophus roseicapilla

Following HRP injections in the cerebellar cortex of the sheep (except the ventral part of the anterior lobe, the flocculus and ventral paraflocculus), labeled cells were evident in motor nuclei of cranial nerves (XII, VII, VI, III, visceromotor nucleus of X and nucleus ambiguus), in the solitary tract nucleus, the nucleus coeruleus and the parabrachial nucleus.     

The diencephalon of the pacific herring,Clupea harengus: Retinofugal projections to the diencephalon and optic tectum

The pattern of retinofugal projections to nuclei in the diencephalon and to the optic tectum was analyzed with horseradish peroxidase and autoradiographic methods in Clupea harengus, a clupeomorph teleost, for comparison with osteoglossomorph, elopomorph, and euteleost teleosts and with non-teleost actinopterygians. Most retinal fibers decussate in the optic chiasm and project to nuclei in the preoptic area, ventral and dorsal thalamus, posterior tuberculum, synencephalon, and pretectum, as well as to the accessory optic nuclei and optic tectum. Some ipsilateral projections do not decussate in the optic chiasm, while others decussate and recross via the supraoptic (minor) and posterior commissures. The pattern of projections is similar to that seen in other actinopterygian fishes with several exceptions. The terminal field usually present lateral to nucleus anterior in the dorsal thalamus is extremely reduced despite the relatively large size of the nucleus. A dense terminal field lies within the cell plate of nucleus corticalis in the pretectum rather than dorsal to it. The tectal hemisphere is composed of two distinct lobules, and the dorsal optic tract projects to the more rostromedial lobule while the ventral optic tract projects to the more caudolateral lobule. The lack of a significant projection to nucleus anterior and the lobular morphology of the optic tectum appear to be apomorphic for Clupea. Other features of the pattern of retinal projections are also analyzed in actinopterygian fishes including Clupea, and several hypotheses are advanced as to which traits are plesiomorphic for actinopterygians and/or for teleosts. © 1993 Wiley-Liss, Inc.     

Calcitonin gene-related peptide in afferents to the cat's cerebellar cortex: distribution and origin.

In the present study, the distribution and origin of calcitonin gene-related peptide (CGRP) were analyzed in the cat's cerebellum. Following incubation in an antibody generated against rat CGRP and processing with the peroxidase anti-peroxidase (PAP) technique, CGRP immunoreactivity (IR) is found in profiles that have morphological characteristics of both simple and complex mossy fibers. However, all mossy fibers are not CGRP-positive. Further, CGRP-IR mossy fibers have a heterogeneous distribution in the cerebellum. In the vermis, the majority of immunoreactive profiles are in lobules VII, VIII, and the dorsal folia of IX. In anterior vermal lobules, only scattered terminals, located primarily at the apex and along the shoulder of the folia, are present. Laterally, CGRP-IR mossy fibers are located in the paramedian lobule, paraflocculus, and crus II. No CGRP fibers or varicosities are observed in any of the cerebellar nuclei. However, CGRP-positive cell bodies are scattered throughout the nuclear neuropil. A double label technique revealed that CGRP-IR mossy fibers arise from neurons located in the lateral reticular nucleus, external cuneate nucleus, inferior vestibular nucleus, and basilar pons. The present findings, taken together with previous data, indicate that cerebellar afferents are chemically heterogeneous. The findings of the present study suggest that precerebellar nuclei that give rise to the mossy fibers that contain CGRP have the potential for playing a complex role in modulating circuitry in the cerebellar cortex of the cat.     

Spinocerebellar projections in the pigeon with special reference to the neck region of the body

Neck sensory information is important for control of head and body movements in all vertebrates. Neuroanatomic tracing methods were used to study the pathways of neck afferent systems. Both the projection of primary afferent fibers and of secondary afferent pathways to brainstem and cerebellum were investigated with the anterograde transport of dextran amines as tracers (biotinylated dextran amine and tetramethyl rhodamine dextran amine). For comparison, the projections of spinocerebellar systems of wing and leg were studied also. Complementary experiments using retrograde tracers (Fast Blue, tetramethyl rhodamine dextran amine, rhodamine isothiocyanate) injected into the cerebellum served to corroborate the results of the anterograde tracing experiments. Primary neck afferent fibers terminated in the spinal gray substance with dense terminal fields in laminae I to V of the dorsal horn and lamina IX of the ventral horn as well as in the marginal nuclei located at the lateral border of the spinal cord. In the brainstem, dense terminal fields were seen in deep layers of the medullary dorsal horn, in the external cuneate nucleus, and in group x. Secondary neck afferents arising from ventral horn cells showed a significant projection to the descending and medial vestibular nuclei and to the medial cerebellar nucleus. Terminals were found both in the anterior and the posterior cerebellum. A quantitative evaluation disclosed that most terminals of neck afferents distributed in lobules II-IV of the anterior cerebellum and lobule IX of the posterior cerebellum. With injections aimed at spinocerebellar neurons located into the cervical and lumbosacral enlargements, no projections were found in the vestibular or deep cerebellar nuclei. Projections from the cervical enlargement were concentrated in lobules III-V and those from the lumbosacral enlargement in lobules III-VI. This points to a rostrocaudal somatotopic representation of neck, wing, and leg in the anterior cerebellum. The results of the retrograde tracing experiments support such a somatotopic organization.     

Parasagittal organization of mossy fiber collaterals in the cerebellum of the mouse

We have observed that WGA-HRP injections in lobule VIII of the mouse result in the labeling of mossy fiber terminals in the anterior lobe (lobules I-V), which are distributed in five distinct parasagittal bands. Injections in the anterior lobe label mossy fiber terminations in lobules VIII and IX. We interpret these results as indicating that an extensive system of mossy fiber collaterals exists between the anterior lobe and lobule VIII (less so to IX), which terminates as discrete parasagittal bands in the anterior lobe. Intermediate bands are thus occupied by fibers that do not send collaterals to the posterior vermis (VII-IX). In an attempt to identify the source(s) of this collateral system we have used double retrograde tracing techniques. Following injections of one tracer in the anterior lobe and another in lobule VIII we observe large numbers of double retrogradely labeled neurons in the lateral reticular nucleus, the basilar pontine nuclei, and the spinal cord. Thus, these mossy fiber sources are the most likely origins for the banded collateral system. Our studies do not allow us to distinguish whether one, or more than one, of these regions contribute to the system.     

Projections to the inferior olive of the cat. II. Comparisons of input from the gracile, cuneate and the spinal trigeminal nuclei

The present experiments compared the projections to the inferior olive of the cat from the gracile, cuneate and spinal trigeminal nuclei. A differential labeling strategy was used for these comparisons. It was found that all three somatic sensory nuclei project to portions of all three major divisions of the contralateral inferior olive. The spinal trigeminal n. may also project less densely to the ipsilateral medial accessory olive. Projections to the dorsal accessory nucleus (DAO) and the medially-adjacent ventral lamella of the principal nucleus are roughly somatotopically organized. Although there is considerable overlap between the projection zones, the gracile n. projects predominantly to lateral DAO, the cuneate n. projects predominantly to medial DAO, and the spinal trigeminal nucleus pars caudalis projects predominantly to the most medial portions of DAO and the ventral lamella of principal olive. Projections to the medial accessory olive, on the other hand, are not as highly organized. Instead, they overlap extensively within a small egg-shaped area in the middle of the caudal half of the nucleus. Whereas all portions of the gracile and cuneate nuclei project to the inferior olive, only the pars caudalis of the spinal trigeminal nucleus appears to do so. These results were compared with the three available olivocerebellar maps as well as with the available behavioral and electrophysiological evidence on cerebellar somatotopic organization. This comparison indicated that the inputs to the cerebellum from the three second-order somatosensory nuclei via the inferior olive appear to be generally consistent with cerebellar somatotopic organization. This consistency is apparent not only with respect to the longitudinally-organized, vermal and paravermal differences in the anterior lobe, but also with respect to the transversely-organized specific somatotopy of the intermediate zone of the anterior lobe and the paramedian lobule.     

Spinocerebellar projections from the thoracic cord in the cat, as studied by anterograde transport of wheat germ agglutinin-horseradish peroxidase

The projection fields of the spinocerebellar tracts arising from thoracic segments were studied by the anterograde transport of wheat germ agglutinin bound to horseradish peroxidase (WGA-HRP) in the cat. Following injections of WGA-HRP into upper and middle thoracic segments, labeled mossy fiber terminals were seen in all lobules of the anterior lobe, lobules VI, VIII, and IX, soblobule VIIb, the paramedian lobule, medial parts of the dorsal paraflocculus, crus I, crus II, and the simple lobule. In the anterior lobe labeled terminals in sublobules IIb-Vb accounted for about 50-60% of the total labeled terminals, of which about 14-18% were present in lobule III and 11-13% were present in lobule IV. The labeled terminals were concentrated within 1.0-1.5 mm from the midline in the vermal region, accounting for about 45-75% of the total in each sublobule. Following injections into lower thoracic segments, labeled terminals tended to distribute more numerously in the lateral part of the vermis and the intermediate region. In the posterior lobe about 5% of the total labeled terminals were distributed in lobules VI and VIII, respectively, and about 16-23% were in the paramedian lobule (mainly sublobules B and C). Cases with injections preceded by a lateral cordotomy have shown that about 65% of the total labeled terminals in each lobule of the anterior lobe were distributed ipsilaterally and 35%, contralaterally. In the paramedian lobule the labeled terminals were distributed predominantly ipsilaterally. Projection fields in the horizontal plane were reconstructed from a series of transverse sections through each lobule. In lobules III and IV the labeled terminals were distributed in nine areas: areas 1-4 in the vermis and areas 5-9 in the intermediate-lateral regions. The two medial areas 1 and 2 were located within 0.5 mm from the midline in zone A1 of Voogd and area 3 appeared to be located in zone A2. Area 4 was located between 0.75 and 1.5 mm in the medial part of zone B. These areas extended longitudinally in the middle part of the apicobasal extent. The five areas in the intermediate-lateral regions were localized in the basal part of the lobule: area 5 in zone C1, areas 6-8 in zones C2 and C3, and area 9 in zone D. Some of these projection areas were identified also in lobules I, II, and V.(ABSTRACT TRUNCATED AT 400 WORDS)     

Cerebellar connections of the trigeminal system in the pigeon (Columba livia)

Wheat germ-agglutinin conjugated horseradish peroxidase (WGA-HRP) was used to delineate trigeminocerebellar connections in the pigeon. Subnucleus oralis of the nucleus of the descending trigeminal tract (nTTD) is the exclusive origin of trigeminal mossy fibers, which terminate in lobules VIII and IXa. The trigemino-olivary projection originates from subnucleus interpolaris of nTTD, but the existence of an additional pathway relaying in the adjacent lateral reticular formation (i.e. the plexus of Horsley) cannot be excluded. Structures linking the trigeminal cerebellar projections to jaw motoneurons were identified within the cerebellar cortex, the deep cerebellar nuclei and the lateral medullary reticular formation, completing a trigeminocerebellar sensorimotor circuit for the jaw.     

Somatosensory Trigeminal Projections to the Inferior Olive,Cerebellum and other Precerebellar Nuclei in Rabbits

We have analysed the pathways through which somatosensory information from the face reaches the inferior olive and the cerebellum in rabbits. We used wheatgerm agglutinin - horseradish peroxidase (WGA-HRP) to trace projections from all parts of the somatosensory trigeminal system to the olive, cerebellar cortex, the cerebellar deep nuclei and the pontine nuclei. Projections to the cerebellar cortex and inferior olive were verified using retrograde transport of WGA-HRP. Two regions of the inferior olive–the medial dorsal accessory olive and the ventral leaf of the principal olive–receive inputs from pars interpolaris (Vi) and rostral pars caudalis (Vc) of the spinal trigeminal nucleus and from the principal trigeminal nucleus (Vp). Another area in the caudal medial accessory olive receives inputs from rostral Vo (pars oralis of the spinal trigeminal nucleus), caudal Vi and Vc. There are trigemino-olivo-cortical inputs to lobule HVI via all these olivary areas and to the paramedian lobe via the principal olive only. Cerebellar cortex–lobules HVI, crus I and II, paramedian lobe and IX–receives direct mossy fibre inputs from Vp, Vo and rostral Vi. The pontine nuclei receive an input only from rostral Vi. We saw no trigeminal projections to other precerebellar nuclei or to the deep cerebellar nuclei. The concentration of face somatosensory cortical inputs, via several pathways, upon lobule HVI may underlie its important role in the regulation of learned and unlearned eyeblinks.     

Cerebellar cortical efferents of the posterior lobe vermis in a prosimian primate (Galago) and the tree shrew (Tupaia)

The topographical organization of cerebellar cortical efferents of the posterior lobe vermis was studied in a prosimian primate (Galago senegalensis) and the tree shrew (Tupaia glis). Two patterns emerge; one which shows longitudinal zones of the entire vermis and a second which shows that individual lobules within the overall longitudinal pattern terminate in specific areas of the ipsilateral medial cerebellar nucleus (NM) and vestibular complex. The posterior lobe vermis consists of a narrow midline portion which projects bilaterally into the NM and a paramidline zone which projects only into the ipsilateral NM. These two zones are probably comparable to, and subdivisions of, Zone A of Voogd ('69). The lateral vermal zone projects primarily into the ipsilateral vestibular complex and/or interposed nuclei and appears to correspond to Zone B of Voogd ('69). Within this overall pattern individual lobules project into specific portions of the NM. From rostral to caudal (lobules VI to IX) terminal fields in the NM shift from dorsal and dorsomedial to ventral and ventrolateral. This is the inverse of the pattern of termination seen in the vestibular complex from lesions of the same lobules where from rostral to caudal (VI to IX) there are overlapping terminal fields from lateral to medial. With the exception of the narrow midline zone cerebellar corticonuclear projections of the posterior lobe vermis are ipsilateral. There is a more complex and more precise relationship between the posterior lobe vermis, NM and vestibular complex than previously suggested.     

Topography and organization of cranial nerve nuclei in the sand lizard, Lacerta agilis

Cobaltic-lysine complex compound was used to label cranial nerves of the ventrolateral (branchiomotor) and dorsomedial (somatomotor) nuclear columns in the sand lizard, Lacerta agilis. The dendritic arborizations and axonal trajectories of neurons of the respective nuclei were reconstructed from serial sections. A fairly uniform neuronal morphology was found in the nuclei of the ventrolateral column: a spindle-shaped perikaryon gave rise to dorsomedial and ventrolateral dendritic trees, the latter arborizing in a characteristic broomlike manner within a narrow region in the lateral white matter. Axons of all neurons converged upon the medial longitudinal fasciculus and after making a hairpin turn formed the corresponding motor roots. A group of small neurons constituted a separate subnucleus within the V motor nucleus. The VII and IX nuclei were fused into a single nuclear complex. The nucleus ambiguus was found dorsal to the XII nucleus and lateral to the dorsal vagal nucleus. The latter nucleus extended rostrally to the caudal pole of the VI nucleus, and its neurons sent axons to the VII, IX, and X nerves. The term "dorsal visceromotor column" designates the extended dorsal vagal nucleus. A number of small polygonal neurons lying scattered in the lateral part of the medulla were labeled via the VII, IX, and X nerves. This loose aggregate of labeled neurons was termed the "lateral visceromotor area." On the basis of nuclear topography and cellular morphology, the existence of a bulbar XI nucleus was excluded. Three different types of neurons could be distinguished in the dorsomedial nuclear column. Neurons with oval or spherical perikarya and radially oriented dendrites constituted the nuclei innervating external eye muscles. Except for the IV nucleus, axons followed a ventral trajectory. The accessory VI nucleus was composed of a second type of neuron with elongated soma and dorsoventral dendrite orientation; the dorsally directed axon turned ventrally at the VI nucleus. The XII nucleus contains a third type of neuron with strongly decussating dendrites. The distinct differences in the neuronal morphology did not support the classical assumption that all of the nuclei of the dorsomedial motor column supply muscles derived from somitic mesoderm. Sensory fibers of the trigeminal nerve formed the familiar spinal tract, which partially decussated in the medullospinal transition zone and could be followed as far as the lumbar segments on the ipsilateral side of the spinal cord. Neurons of the mesencephalic root of the trigeminal nerve were localized in the optic tectum; their descending fibers joined the medial aspect of the spinal tract.(ABSTRACT TRUNCATED AT 400 WORDS)     

The central projections of the trigeminal,facial and anterior lateral line nerves in the carp (Cyprinus carpio L.)

The central projections of the trigeminal, facial and anterior lateral line nerves were studied in the carp (Cyprinus carpio) by the Nauta and Fink-Heimer silver techniques following rhizotomy. Degenerating trigeminal fibers were found projecting on the nucleus of the descending trigeminal root and on the medial funicular nucleus. The former can be subdivided in five portions lying dorsal to the various cranial motor nuclei. The afferent facial fibers could be traced into the facial, glossopharyngeal and vagal lobes, while the anterior lateral line nerve projects on rostral, medial and caudal parts of the medial nucleus and on the eminetia granularis. The anterior lateral line nerve can be divided into a dorsal and a ventral root, each following the same course. The role trigeminal and facial nerves play in proprioception of respiratory muscles is discussed.