Spinal cord projections from the medial cerebellar nucleus in tree shrew (Tupaia glis)

The tree shrew cerebellum atlas: Systematic nomenclature, neurochemical characterization, and afferent projections

The cerebellum is involved in the control of movement, emotional responses, and reward processing. The tree shrew is the closest living relative of primates. However, little is known not only about the systematic nomenclature for the tree shrew cerebellum but also about the detailed neurochemical characterization and afferent projections. In this study, Nissl staining and acetylcholinesterase histochemistry were used to reveal anatomical features of the cerebellum of tree shrews (Tupaia belangeri chinensis). The cerebellar cortex presented a laminar structure. The morphological characteristics of the cerebellum were comprehensively described in the coronal, sagittal, and horizontal sections. Moreover, distributive maps of calbindin-immunoreactive (-ir) cells in the Purkinje cell layer of the cerebellum of tree shrews were depicted using coronal, sagittal, and horizontal schematics. In addition, 5th cerebellar lobule (5Cb)-projecting neurons were present in the pontine nuclei, reticular nucleus, spinal vestibular nucleus, ventral spinocerebellar tract, and inferior olive of the tree shrew brain. The anterior part of the paramedian lobule of the cerebellum (PMa) received mainly strong innervation from the lateral reticular nucleus, inferior olive, pontine reticular nucleus, spinal trigeminal nucleus, pontine nuclei, and reticulotegmental nucleus of the pons. The present results provide the first systematic nomenclature, detailed atlas of the whole cerebellum, and whole-brain mapping of afferent projections to the 5Cb and PMa in tree shrews. Our findings provide morphological support for tree shrews as an alternative model for studies of human cerebellar pathologies.

Enkephalin-immunoreactive fastigial neurons in the rat cerebellum project to upper cervical cord segments

By using enkephalin immunohistochemistry combined with retrograde fluorescent labelling, a great majority of neurons in the rat cerebellum sending their axons to the spinal cord were shown to contain enkephalin immunoreactivity. These neurons were numerous and clustered in the fastigial nucleus but far less abundant in other cerebellar nuclei. Enkephalin-immunoreactive fibers present in the ventral horn and the central cervical nucleus of upper cervical cord segments almost completely disappeared contralaterally following kainic acid-induced cell loss in the fastigial nucleus. The results indicate that fastigial and some other cerebellar nucleus neurons provide enkephalin-containing projections toward these spinal sites.

Course of spinocerebellar axons in the ventral and lateral funiculi of the spinal cord with projections to the anterior lobe: an experimental anatomical study in the cat with retrograde tracing techniques

The fiber course of the spinocerebellar tracts in the ventral and lateral funiculi of the cat spinal cord were studied by a new approach, making cordotomies at different spinal levels or lesions of the restiform body followed by injections of HRP or WGA-HRP into the anterior cerebellar lobe. The retrogradely labeled axons showed characteristic distribution patterns related to the level and extent of the lesions. The results show the following. 1) The dorsal spinocerebellar tract (DSCT) originating ipsilaterally from the thoracic and upper lumbar segments ascends in the dorsolateral fasciculus. It undergoes a dorsal shift during its rostral course. The tract is topically arranged and passes through the restiform body. 2) The ventral spinocerebellar tract (VSCT) arising contralaterally from lower thoracic, lumbar, and more caudal segments passes via the ventral funiculus and ascends in the ventrolateral fasciculus. This tract is also topically arranged. It makes a lateral and then a dorsal shift during its ascending course. The main portion of the VSCT enters the cerebellum via the superior cerebellar peduncle. A minor portion originating from the sacrococcygeal region enters via the restiform body. 3) The spinocerebellar fibers originating ipsilaterally from the cervical enlargement ascend in the lateralmost part of the lateral funiculus in the area between the dorsolateral and ventrolateral fasciculi. These fibers form two groups, one passing through the restiform body, the other through the superior cerebellar peduncle. 4) The spinocerebellar fibers originating contralaterally from the central cervical nucleus pass through the ventral funiculus and ascend in the lateralmost part of the lateral funiculus, mainly in the ventrolateral fasciculus. Most of the fibers seem to pass through the superior cerebellar peduncle.

Organization of the cerebellum in the pigeon (Columba livia): II. Projections of the cerebellar nuclei

The projections of the deep cerebellar nuclei in the pigeon have been delineated using autoradiographic and histochemical (WGA-HRP) tracing techniques. A medial (CbM) and lateral (CbL) cerebellar nucleus are recognized and CbM may be further partitioned into internal, intermediate, and intercalate divisions. As in mammals, most extracerebellar projections of CbM travel in the fasciculus uncinatus (FU); the rest travel with those of CbL in the brachium conjunctivum (BC). In the pigeon, both of these pathways are bilaterally but primarily contralaterally projecting systems. FU is a predominantly descending tract, with terminations within (1) the vestibular complex, (2) a column of contiguous medial reticular nuclei from pontine to caudal medullary levels; (3) the plexus of Horsley portion of the parvicellular reticular formation, continuing through the nucleus centralis medullae oblongatae, pars dorsalis, into intermediate layer VII of the cervical spinal cord, down to cervical segment 8-9; (4) the lateral reticular nucleus and the paragigantocellular reticular nucleus; (5) the dorsal lamella of the inferior olive. Rostrally FU terminals are found in the locus ceruleus and dorsal subcerulean nucleus. Minimal FU projections are also seen to the motor trigeminal nucleus and the subnucleus oralis of the descending trigeminal system. A small projection from the intercalate division of CbM travels in BC and projects upon the midbrain central grey, the intercollicular nucleus, the lateral tectal periventricular grey, the stratum cellulare externum and, sparsely, upon the dorsolateral thalamus. The bulk of BC originates from the lateral cerebellar nucleus and consists of a massive ascending and a small descending branch. The ascending system projects upon the red nucleus and the dorsally adjacent interstitial nucleus of Cajal and midbrain central grey, the prerubral fields continuing into the stratum cellulare externum, the nucleus intercalatus thalami, the ventrolateral thalamic nucleus, the medial spiriform nucleus, the nucleus principalis precommissuralis, the nucleus of the basal optic root, the nucleus geniculatus lateralis pars ventralis, the dorsolateral thalamus, including the dorsal intermediate posterior, and the dorsolateral intermediate and anterior nuclei. BC also contains axons from the infracerebellar nucleus, which projects upon the trochlear and the oculomotor nuclei. The descending branch of BC distributes to the papilioform nucleus, the medial pontine nucleus, the gigantocellular and paramedian reticular nuclei, and, minimally, the rostral portions of the medial column and ventral lamella of the inferior olive. Taken in conjunction with data on amphibia and reptiles the present findings suggest that the fundamental ground plan of vertebrate cerebellar organization involves a medial and lateral cerebellar nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)

Nonsomatic Cerebellar Circuits

The cerebellum not only receives extensive proprioceptive input from the periphery but also has bidirectional monosynaptic connections with the hypothalamus. This latter structure, in turn, is reciprocally interconnected with brain-stem visceral centers that also project to the cerebellum. Through these connections, information derived from somatic receptors that arrives at the cerebellum can directly influence visceral centers and circuits. It is suggested that the visceral responses seen during locomotor activity can be continuously monitored and partially regulated through such connections.

Origins of the descending spinal projections in petromyzontid and myxinoid agnathans

The origins of the descending spinal pathways in sea lampreys (Petromyzon marinus), silver lampreys (Ichthyomyzon unicuspis), and Pacific hagfish (Eptatretus stouti) were identified by the retrograde transport of horseradish peroxidase (HRP) placed in the rostral spinal cord. In lampreys, the majority of HRP-labeled cells were located along the length of the brainstem reticular formation in the inferior, middle, and superior reticular nuclei of the medulla, mesencephalic tegmentum, and nucleus of the medial longitudinal fasciculus. Labeled reticular cells included the Mauthner and Müller cells. Horseradish-peroxidase-filled cells were also present in the descending trigeminal tract, intermediate and posterior octavomotor nuclei, and a diencephalic cell group, the nucleus of the posterior tubercle. As in lampreys, the reticular formation of the Pacific hagfish was the largest source of descending afferents to the spinal cord. Labeled cells were found in the dorsolateral and ventromedial reticular nuclei, the dorsal tegmentum at the juncture of the medulla and midbrain, and the nucleus of the medial longitudinal fasciculus. Additional medullary cells projecting to the cord were located in the perivagal nucleus, the central gray, and the anterior and posterior magnocellular octavolateralis nuclei. The existence of reticulospinal and possible vestibulo-, trigemino-, and solitary spinal projections in lampreys and hagfishes and the wide distribution of these pathways in jawed vertebrates suggest that they evolved in the common ancestor of gnathostomes and both groups of jawless fishes. However, descending spinal pathways from the cerebellum, red nucleus, and telencephalon appear to be gnathostome characters.

Collateralization of cerebellar efferent projections to the paraoculomotor region, superior colliculus, and medial pontine reticular formation in the rat: a fluorescent double-labeling study

Collateralization of cerebellar efferent projections to the oculomotor region, superior colliculus (SC), and medial pontine reticular formation (mPRF) was studied in rats using fluorescent tracer substances. In one group, True Blue (TB) was injected into the oculomotor complex (OMC), including certain paraoculomotor nuclei and supraoculomotor ventral periaqueductal gray (PAG), and Diamidino Yellow (DY) was injected into the medial pontine reticular formation (mPRF) or pontine raphe. The largest number of single-TB-labeled (paraoculomotor-projecting) cells was observed in the medial cerebellar nucleus (MCN) and posterior interposed nucleus (PIN), whereas the largest number of single-DY-labeled (mPRF-projecting) cells was in the MCN. Double-TB/DY-labeled cells were present in the caudal two-thirds of the MCN, suggesting that some MCN neurons send divergent axon collaterals to the paraoculomotor region and mPRF. In another group, TB was injected into the SC and DY into the mPRF. The largest number of single-TB-labeled (SC-projecting) cells was in the PIN, although a considerable number of cells was observed in the caudal MCN, and ventral lateral cerebellar nucleus (LCN). Single-DY-labeled (mPRF-projecting) neurons were primarily located in the central and ventral MCN, but were also present in the lateral anterior interposed (AIN) and in the LCN. Double-TB/DY-labeled neurons were observed in the caudal two-thirds of the MCN and in the central portion of the LCN. The most significant new findings of the study concerned the MCN, which not only contained neurons that projected independently to the paraoculomotor region, SC, and mPRF, but also contained a considerable number of cells which collateralized to project to more than one of these nuclei. The possibility that the MCN projects to the supraoculomotor ventral PAG (containing an oculomotor interneuron system) and to the mPRF, which in the cat and monkey contain neural elements essential to the production of saccadic eye movements, is discussed. The anatomical findings suggest that the MCN in the rat plays an important role in eye movement.

The cerebellar and vestibular nuclear complexes in the turtle. I. Projections to mesencephalon, rhombencephalon, and spinal cord

Cerebellar and vestibular projections were investigated in the turtle Pseudemys scripta elegans following injection of 35S-methionine into the cerebellar and vestibular nuclear complexes at various locations. Fibers arising from the cerebellar nuclei were traced via the cerebellar commissure to the contralateral vestibular nuclear complex (particularly the n. vestibularis inferior and n. vestibularis ventrolateralis) and caudal rhombencephalic tegmentum. Ascending projections crossing the midline in the ventral isthmomesencephalic tegmentum terminated in the contralateral red nucleus and nuclei of the fasciculus longitudinalis medialis (f lm). Vestibular projections ascending mainly via the f lm terminated in the nuclei of the f lm, the nuclei of the posterior commissure, and particularly the extraocular motor nuclei. Vestibulo-ocular projections arising from the rostral vestibular nuclear complex were almost exclusively ipsilateral; those from the caudal vestibular nuclear complex were bilateral. Evidence for a topographic organization of the projections to the trochlear and oculomotor nuclei was also obtained. There were some vestibular projections to the contralateral rhombencephalic tegmentum and n. vestibularis inferior. Spinal projections coursing within the ipsilateral ventral descending tract and the ipsilateral fasciculus longitudinalis medialis were found to arise from both rostral and caudal vestibular regions. The caudal vestibular nuclear complex in addition gave rise to fibers descending in the contralateral fasciculus longitudinalis medialis. Evidence for the existence of labeled fibers crossing at spinal levels was also obtained. Vestibulospinal terminations appeared restricted to the ventral horn.

The origins of descending spinal projections in lepidosirenid lungfishes

The origins of descending spinal projections in the lepidosirenid lungfishes were identified by retrograde transport of horseradish peroxidase (HRP) introduced into the rostral spinal cords of juvenile African (Protopterus annectans and Protopterus amphibians) and South American (Lepidosiren paradoxa) lungfishes. Standard HRP histochemistry revealed retrogradely labeled neurons in the nucleus of the medial longitudinal fasciculus, midbrain tegmentum, red nucleus, optic tectum, mesencephalic trigeminal nucleus, granule cell layer of the cerebellum, superior, middle, and inferior medullary reticular nuclei, magnocellular and descending octaval nuclei, region of the descending trigeminal tract, solitary complex, and the margins of the spinal gray matter anterior to the spinal HRP implant. A small number of retrogradely labeled neurons were also present in the ventral thalamus of Protopterus. A descending spinal projection from the forebrain was not evident in either genus of lepidosirenid lungfishes. The presence of projections to the spinal cord from the diencephalon, medial reticular formation of the midbrain and medulla, octaval (vestibular) nuclei, solitary complex, and probable nucleus of the descendin trigeminal tract in lungfishes and their overall similarity to comparable projections in other vertebrates suggest that these pathways are among those representative of the primitive pattern of descending spinal projections in vertebrates.

An HRP study of hypothalamo-cerebellar and cerebello-hypothalamic connections in squirrel monkey (Saimiri sciureus)

This study describes the distribution of labeled hypothalamic neurons in squirrel monkey following pressure injections of horseradish peroxidase (HRP) into cerebellar cortex and the pattern of labeling in the cerebellar nuclei subsequent to iontophoretic injections localized in the hypothalamus. Two types of HRP (HRP and a wheat germ agglutinin conjugate, HRP-WGA) were used as tracers; tetramethylbenzidine was the chromogen. Retrogradely filled neurons were found in lateral (LHAr) and posterior (PHAr) hypothalamic areas, and in the lateral mammillary (LMNu) and supramammillary (SMNu) nuclei following injections into ansiform and paramedian lobules and into the paraflocculus. Labeled cells were occasionally seen in the medial mammillary nucleus (parafloccular cases) and among fascicles of the mammillothalamic tract (all posterior lobe cases) immediately above the medial nucleus. After injections into the anterior lobe, labelling was again found in the LHAr, PHAr, LMNu, and SMNu. In addition, retrogradely filled cells were present in ventromedial, dorsomedial, and dorsal hypothalamic nuclei and in the dorsal hypothalamic area. Labeled cells were occasionally found among fascicles of the fornix along its intrahypothalamic course. In general, labeling extends into slightly more rostral hypothalamic levels in anterior lobe cases when compared to posterior lobe experiments. We interpret these data as indicating that some hypothalamic neurons project directly to the cerebellar cortex (i.e., hypothalamo-cerebellar fibers); this projection is bilateral with an ipsilateral preponderance. In experiments with injections of HRP-WGA into the cerebellar nuclei, anterogradely filled axons were traced into the contralateral PHAr and LHAr; this was suggestive of a direct cerebello-hypothalamic projection. Following iontophoretic injections localized in the LHAr and the medial mammillary nucleus, labeling was seen in the medial (NM), posterior interposed (NIP), and lateral (NL) cerebellar nuclei; this is essentially a contralateral projection. Retrogradely labeled cells were found in the rostral and ventral NM, the ventral and dorsocaudal NL, and diffusely throughout the NIP. On the basis of the known distribution of cerebello-thalamic fibers and other criteria, these labeled cells are representative of a true cerebello-hypothalamic projection. It is suggested that the cerebellum, through these pathways, may have a relatively direct influence on visceral centers in the brainstem and spinal cord.

Distribution and structural characterization of neurons giving rise to descending spinal projections in the turtle, Pseudemys scripta elegans

Descending spinal projections were investigated in the turtle Pseudemys scripta elegans following injections of horseradish peroxidase and/or radioactive wheat germ agglutinin into the spinal cord at various levels. Using various planes of section the cells of origin in the brainstem, cerebellum, and diencephalon were characterized according to their size, dendritic tree, and precise location. Projections to levels as far caudal as the lumbar spinal cord were found to arise from medial and lateral rhombencephalic reticular fields, including the perihypoglossal complex, the nucleus raphe inferior, and the locus coeruleus; from certain subdivisions of the vestibular complex (ipsilateral subnucleus (subn.) ventrolateralis, contralateral subn. ventromedialis, and possibly subn. tangentialis); from the motor trigeminal nucleus; from the contralateral red nucleus, the ipsilateral nucleus (n.) interstitialis of the fasciculus longitudinalis medialis (flm) and from the hypothalamus. Fibers to high cervical levels arose from neurons within the dorsolateral and superior vestibular nuclei, the lateral cerebellar nucleus, the mesencephalic trigeminal nucleus, and from neurons of the optic tectum. Low cervical and thoracic spinal levels were reached by fibers from the torus semicircularis n. laminaris, the n. of the flm, the medial cerebellar nucleus as well as from the n. vestibularis inferior and the principal and descending trigeminal nuclei.

Divergent axon collaterals from rat cerebellar nuclei to diencephalon, mesencephalon, medulla oblongata and cervical cord. A fluorescent double retrograde labeling study

The existence of divergent axon collaterals of neurons in the deep cerebellar nuclei has been investigated in rat by means of the fluorescent retrograde double labeling technique. The results have led to the following conclusions. A. Many of the neurons in the lateral, the interpositus as well as the caudal half of the medial nucleus project to the diencephalon. Some of these neurons distribute divergent axon collaterals to the superior colliculus, but few neurons project only to the latter structure. B. Some of the deep cerebellar neurons located laterally, i.e. in the dorsomedial part of the lateral nucleus, as well as some others located medially, i.e. in the medial part of the interpositus nucleus and the adjoining part of the medial nucleus, distribute divergent axon collaterals to the diencephalon and the spinal cord. C. Deep cerebellar neurons located laterally: in the cell group of the dorsolateral hump (Dlh) and in the adjoining lateral part of the interpositus nucleus, as well as some other located medially, i.e. in the dorsolateral part of the median nucleus (Mdlp), distribute divergent axon collaterals to the diencephalon and to the medulla oblongata, probably primarily its medial reticular formation. However, only few of the neurons, which distribute descending collaterals to the spinal cord or the medulla oblongata, distribute ascending collaterals to the superior colliculus. D. After injections in the medulla oblongata a population of small sized single labeled neurons was encountered especially in the lateral and interpositus nuclei. On the basis of other findings in rat they were assumed to represent cerebello-olivary neurons.

Divergent collaterals from deep cerebellar neurons to thalamus and tectum, and to medulla oblongata and spinal cord: retrograde fluorescent and electrophysiological studies

In cat the existence of collaterals from deep cerebellar neurons, which project to mesencephalon and thalamus has been investigated anatomically by means of the multiple retrograde fluorescent tracer technique as well as electrophysiologically by means of conventional antidromic techniques. Both sets of data indicate that several neurons in the medial nucleus, which project to mesencephalon and thalamus, also distribute collaterals to medulla oblongata and spinal cord. These branching neurons were principally located in the caudal and intermediate portions of the medial nucleus. The electrophysiological data in addition indicate that the branching point of the neurons in the medial nucleus is located relatively close to the cell soma. The anatomical findings show a further group of branching neurons in the lateral nucleus at the border with the interpositus nuclei. The majority of these latter neurons distribute collaterals to medulla oblongata but some distribute collaterals to spinal cord. However, it could not be decided as yet whether the collaterals to the medulla oblongata terminate either in medullary medial reticular formation or in inferior olive or in both.

Cells of origin of pathways descending to the spinal cord in some quadrupedal reptiles

The cells of origin of pathways descending to the spinal cord have been determined in several quadrupedal reptiles, viz., the turtle Pseudemys scripta elegans and Testudo hermanni and the lizards Tupinambis nigropunctatus and Varanus exanthematicus, following a technique introduced by Kuypers and Maisky ('75). This technique was very effective in producing retrograde transport of HRP to a great many neurons in the hypothalamus and in the brain stem. Projections from the hypothalamus (the nucleus paraventricularis and the nucleus periventricularis hypothalami), the interstitial nucleus of the film, the nucleus ruber, the nucleus of Edinger-Westphal, the locus coeruleus, the subcoeruleus area, a conspicuous cell group comparable to Kuypers and Maisky's (75, '77) lateral pontine area, the magnocellular reticular formation, the ventrolateral, ventromedial, and descending vestibular nuclei, the dorsal motor nucleus of the vagus, and the nucleus of the solitary tract, reach at least as far as the lumbar intumescence. Projections from two somatosensory nuclei, i.e., the nucleus descendens nervi trigemini and the nucleus funiculi dorsalis, as well as the laminar nucleus of the torus semicircularis, have been demonstrated to at least the ninth spinal segment. The two deep cerebellar nuclei, particularly the medial cerebellar nucleus, were found to project contralaterally to the spinal cord, in the lizard Varanus exanthematicus at least as far as the seventh segment; in the turtles studied so far, only projections as far caudal as the fourth spinal segment could be demonstrated. Data on the funicular trajectory of various descending pathways could also be obtained. It seems likely that in the reptiles studied, in addition to rubrospinal and reticulospinal pathways, projections from the hypothalamus, the nucleus of Edinger-Westphal, the cell group comparable to the mammalian lateral pontine area, the locus coeruleus, and subcoeruleus area, and the nucleus of the solitary tract pass via the lateral funiculus. The pathways descending from the hypothalamus and brain stem to the spinal cord in the quadrupedal reptiles studied appear to show remarkable similarities to pathway in mammals as regards their cells of origin as well as their funicular trajectory. It seems likely that some of the projections demonstrated, viz., from the locus coeruleus, at least part of the cell group comparable to the lateral pontine area, as well as the cells in and around the dorsal motor nucleus of the vagus, are noradrenergic pathways.