Medial Cerebellar Nucleus Research Articles

Localization of fibroblast growth factor-9 mRNA in the rat brain.

We examined the localization of fibroblast growth factor-9 (FGF-9) mRNA in the rat brain by in situ hybridization. FGF-9 mRNA was moderately or weakly expressed in widespread regions including the olfactory bulb, caudate putamen, cerebral cortex, hippocampus, thalamus, hypothalamus, midbrain, brainstem and cerebellum. However, FGF-9 mRNA was also strongly expressed in several specific nuclei including the red nucleus and oculomotor nucleus in the midbrain, the vestibular nucleus and facial nucleus in the brainstem and the medial cerebellar nucleus, interposed cerebellar nucleus and lateral cerebellar nucleus in the cerebellum. The cellular localization of FGF-9 mRNA indicated that the mRNA in the rat brain was expressed preferentially in neurons, although FGF-9 was originally isolated from human glioma cells. The localization profile of FGF-9 mRNA is different from those of aFGF, bFGF and FGF-5 mRNAs reported previously. The present findings indicate that FGF-9 has a unique role in the brain.

Mutism and Cerebellar Dysarthria after Brain Stem Surgery

Transient mutism resolving to cerebellar speech after posterior fossa surgery is a well-recognized phenomenon, particularly in pediatric patients. The anatomic basis for this postoperative functional change is unclear but may reside in the dominant superior cerebellar hemisphere or the medial deep cerebellar nuclei. We report a case of an 8-year-old girl who presented for surgical resection of a cavernous malformation of the right pons (at the level of the middle cerebellar peduncle) after hemorrhage. Preoperatively, her complaints consisted of contralateral motor deficits. She had normal speech. Her lesion was resected through a subtemporal approach to the pons. She awoke unable to speak. She was able to communicate through a variety of verbal cues, including sign language. Her mutism lasted 12 days after which she underwent a prolonged period of slowly resolving cerebellar dysarthria. Her preoperative motor deficits also slowly resolved. This is the first reported case of mutism resolving to cerebellar dysarthria after a supratentorial approach to the brain stem. We discuss the anatomic basis for postoperative mutism in light of previous observations combined with the unusual finding of mutism after pontine surgery. In particular, reports of mutism after bilateral cerebellar hemispheric injury, bilateral or unilateral medial deep nuclear injury, and, now, pontine tegmental injury implicate the superior cerebellar hemispheres, the deep cerebellar nuclei, and the nuclear outflow through the superior cerebellar peduncle as the anatomic bases for cerebellar participation in the production of human speech.

Age-related and region-specific increase in number of concentric lamellar bodies in axon terminals and presynaptic axons in central nervous system of groggy mutant rat.

In some regions of the central nervous system (CNS) of the groggy rat, a mutant with a movement disorder, concentric lamellar bodies (CLBs) were formed in numerous axon terminals and presynaptic axons. These bodies were counted electron microscopically in the lateral cerebellar nuclei of Slc:Wistar and groggy mutant rats at 20 to 180 days of age. In the Slc:Wistar rat groups, the mean numbers of axonal CLBs were mostly under 1.0 per 100 microns2, except for the 30-day-old rat group which showed a value of 1.7. In the groggy rat groups, the numbers of axonal CLBs greatly increased from 40 days of age onward, reaching the maximum mean number of 23.7 per 100 microns2 in the 90-day-old rat group and subsequently decreasing; however, significant numbers were still present in the 180-day-old rat group. Since these bodies have been reported to contain an acid phosphatase (ACPase), the regional specificity of their appearance in the CNS was examined by light and electron microscopic ACPase histochemistry. In the 90- and 180-day-old groggy rats, numerous particulate deposits of ACPase reaction products were found in the neuropil of the lateral, interposed and medial cerebellar nuclei, the superior, lateral and spinal vestibular nuclei, and the spinal gracile nuclei. By electron microscopy, the particulate deposits in the cerebellar and vestibular nuclei were confirmed as the CLBs in axon terminals, while those in the gracile nuclei were revealed to be the dystrophic axons. Thus, it was suggested that the axon terminals and presynaptic axons, having a high capacity to form the CLBs in the groggy rats from 40 days of age onward, belong to the Purkinje cells.

The origin of serotoninergic afferents to the cat's cerebellar nuclei

In the cat, serotoninergic (5HT) axons and terminals form a dense plexus that is present throughout the granule cell and Purkinje cell layers of the cerebellar cortex and all of the cerebellar nuclei. The intent of the present study was to identify the source of 5HT fibers in the cerebellar nuclei. The medial, interposed, and lateral cerebellar nuclei were selectively injected with either rhodamine or fluorescein-labeled latex microspheres that were retrogradely transported to brainstem neurons. Transverse sections of the brainstem were processed with a primary antibody to 5HT and secondary antibody tagged with either rhodamine or fluorescein. The location of neurons containing both serotonin-like immunoreactivity and retrogradely transported microspheres was plotted. All three of the cerebellar nuclei receive 5HT afferents from the nucleus locus coeruleus, the dorsal raphe nucleus, and the dorsal tegmental nucleus. In addition, the medial nucleus receives projections from the superior central nucleus, the nucleus raphe obscurus, the nucleus raphe magnus, and the periolivary reticular formation. The interposed nuclei receive additional projections from the nucleus raphe magnus, whereas the lateral nucleus receives additional projections from the superior central nucleus. In conclusion, the 5HT projections to the cerebellar nuclei do not appear to be collaterals of those projecting to the cortex (Kerr and Bishop, J Comp Neurol 304:502-515, 1991). These findings suggest that, although the cortex and nuclei are anatomically and physiologically related, they do not process all information in parallel.

Angiotensin II receptor subtypes and angiotensin-converting enzyme in the fetal rat brain

Angiotensin II (ANG II) receptor subtypes (AT 1, displaced by losartan, and AT 2, displaced by CGP 42112A) were characterized by quantitative autoraography after incubation with the ANG II agonist [ 125I]Sar 1-ANG II, in specific brain nuclei of 19-day-old rat embryos. Binding to AT 1 receptors, located in the subfornical organ, paraventricular nucleus, nucleus of the solitary tract and choroid plexus, was sensitive to incubation with GTPγS. The sensitivity of AT 2 receptors to GTPγS was heterogeneous. In the ventral thalamic, rostral hypoglossal and medial geniculate nuclei, and in the locus coeruleus, binding to AT 2 receptors was sensitive to GTPγS and these areas belong to the AT 2A subgroup. Conversely, in the inferior olive, medial (fastigial) cerebellar nucleus and caudal part of the hypoglossal nucleus, areas belonging to the AT 2B subgroup, binding was insensitive to GTPγS. AT 2 receptors were also present in cerebral arteries. In the fetal anterior pituitary, AT 1 receptors predominated. The angiotensin-converting enzyme (ACE; EC 3.4.15.1) was studied by autoradiography with the selective inhibitor [ 125I]351A. In 19-day-old embryos, ACE was highly expressed in chroid plexus, with high concentrations in subfornical organ, posterior pituitary and cerebral arteries. No ACE binding was detected in extrapyramidal structures or anterior pituitary in 19-day-old embryos.

Role of the fastigial nucleus in generalized seizures as demonstrated by GABA agonist microinjections.

The cerebellum is electrically and metabolically active during seizures. Numerous studies have also shown that cerebellar electrical stimulation and lesions of the cerebellar cortex or nuclei influence seizure threshold, but there are significant contradictions, with different effects observed even in investigations using the same species and similar seizure types and experimental manipulations. Discrete intracerebral microinjection of neuroactive agents has been used to characterize the way in which other brain regions control seizures, but has not been applied to the cerebellar systems. This approach has advantages because effects are restricted to specific receptors and spare passing axons; experimental variables also can be simply specified and reproduced. We used this method to characterize the role of the cerebellar nuclei in seizures and to determine if observed effects could be reproduced with different agents at different doses. Effects of bilateral control microinjections in the fastigial (medial) cerebellar nucleus were compared with different doses of the GABAA agonist piperidine-4-sulfonic acid and the GABAB agonist (-)baclofen (Bf). Soon after injection, the animals were ataxic. After 4 min, seizures were induced by timed continuous intravenous (i.v.) bicuculline (BIC) infusion. Both GABA agonists produced significant reductions in myoclonic, clonic, and tonic seizure thresholds. Injections just dorsal or anterior to this nucleus and bilateral dentate (lateral) nucleus injections had little effect on seizures. These results demonstrate that the cerebellar system does control seizures, but does not provide support for the early concept that cerebellar stimulation and systemic phenytoin block seizures through inhibition of cerebellar nuclei secondary to Purkinje cell activation.

Cerebellar nuclear projections from the basilar pontine nuclei and nucleus reticularis tegmenti pontis as demonstrated with PHA-L tracing in the rat.

Small iontophoretic placements of the orthogradely transported axonal tracer Phaseolus vulgaris leucoagglutinin (PHA-L) were made in portions of the basilar pontine nuclei (BPN) or nucleus reticularis tegmenti pontis (NRTP) to determine if these cell groups provide projections to the cerebellar nuclei (CN) in the rat and if so, to visualize the morphology of the axons and terminals and illustrate any topographical organization in this system. Axons that originated from BPN or NRTP neurons and contained PHA-L were visualized by an immunohistochemical procedure that involved sequential incubation of tissue sections with goat anti-PHA-L antibody, biotinylated rabbit anti-goat immunoglobulin, and a biotin-avidin-peroxidase conjugate. Following injections of PHA-L restricted to ventral and medial portions of the BPN, labeled fibers were observed in the brachium pontis, the white matter dorsal to the CN, and to a lesser extent, in the white matter of the parafloccular stalk. Labeled preterminal axons entered the CN and gave rise to beaded axons that arborized primarily within dorsal portions of the lateral, interposed, and medial cerebellar nuclei. Injections of PHA-L restricted to either lateral portions of the BPN or ventrolateral regions of NRTP produced labeled fibers in the cerebellum that most frequently involved the parafloccular stalk and ventral portions of the CN. In contrast, dorsomedial NRTP injections resulted in the presence of labeled fibers both in the dorsal cerebellar white matter and the parafloccular stalk as well as dorsal and ventral portions of the CN. With the exception of the rostral and medial territory of interpositus anterior which received very sparse input, all portions of each CN subdivision seemed to exhibit some degree of terminal labeling. The density of labeled axon terminals in the CN appeared to be somewhat greater in the NRTP-injected cases compared to BPN-injected animals. These observations indicate that in the rat, both the BPN and NRTP contain neurons whose axons distribute to the CN. It is likely that most of the axons which project to the CN are collaterals of fibers that continue into the cerebellar cortex as mossy fibers but confirmation of this point must await further investigation. In light of the extensive projections from the cerebral cortex to the BPN and NRTP, this axonal system provides the cerebral cortex with a relatively direct route of access to the CN via one synapse in the BPN or NRTP.

Neurons with strongly negative-charged surface-coats in adult rat brain as detected by staining with cationic iron colloid.

Light microscopy of tissue sections stained either with cationic iron colloid (pH 1.0-2.0) and nuclear fast red or with this colloid and thionin showed that the adult rat brain contains a considerable number of neurons which are strongly negative-charged by being coated with sulfated proteoglycans such as chondroitin sulfates. These neurons are distributed mainly in the cerebral cortex, hippocampus, zona incerta, medial and lateral cerebellar nuclei, ventral pontine nuclei and certain other areas. In the hippocampal formation, the strongly negative-charged cells seem identical with the GABAergic inhibitory interneurons reactive to the lectin Vicia villosa agglutinin. Neurons, including the GABAergic Purkinje's cells, of the cerebellar cortex showed no reaction to our cationic iron colloid at pH values of 1.0-2.0. Many non-GABAergic pyramidal cells in the lamina ganglionalis of cerebral cortex and many non-GABAergic large neurons of the ventral pontine nuclei were highly reactive to our colloid at pH values of 1.0-2.0. This suggests that our cationic iron colloid at pH values of 1.0-2.0 mainly stains certain subtypes of GABAergic neurons as well as some non-GABAergic neurons projecting long associational or commissural fibers.

Development of the cerebellar cortical efferent projection: an in-vitro anterograde tracing study in rat brain slices

This study reports the results of an anterograde HRP analysis of the development of cerebellar cortical efferents studied in-vitro with cerebellum-brainstem slices from embryonic (E-18) through newborn rats. From E-18, Purkinje cells in the medial region of the cerebellum are seen to project to the medial cerebellar and vestibular nuclei, their appropriate targets in the adult animal. Thus, the cortical efferent system is forming during late embryogenesis and may establish synaptic contacts with target cells as early as E-20.

Evidence of an x zone in lobule V of the squirrel monkey (Saimiri sciureus) cerebellum: the distribution of corticonuclear fibers.

The distribution of corticonuclear fibers to medial-most parts of the posterior interposed nucleus (NIP) from lateral areas of the vermis was studied in the squirrel monkey (Saimiri sciureus), using a silver impregnation method. The origin and course of degenerated fibers were studied in serial sections. The distribution pattern of corticonuclear fibers from a series of small well localized lesions placed in the vermis and paravermal cortex of lobule V is compatible with the interpretation that an x zone is present in Saimiri. A comparison of the positions of lesions and the trajectory of fibers arising therein suggests that corticonuclear input to medial-most parts of the NIP originated from a narrow cortical area (about 0.5-0.7 mm wide) located between a cortical area projecting into the medial cerebellar nucleus (the A zone) and a laterally adjacent area (the B zone) which related to the lateral vestibular nucleus. This NIP-projecting cortical area, located about 1.7 mm to 2.5 mm off the midline in lobule V, is interpreted as the x zone in this primate; it extends from lobule IV into lobule VI in squirrel monkey. Corticonuclear fibers of zone x in this primate form a comparatively small terminal field in the medial-most portions of NIP. This contrasts with the distribution of corticonuclear fibers of the C2 zone which consistently distribute to terminal fields that are shifted into more central areas of NIP. There appears to be no overlap of the corticonuclear terminal fields in the NIP for zone x versus the C2 zone. These results were correlated with data from the literature on the distribution of olivocerebellar fibers to the x zone and the C2 zone and the arrangement of cerebellar nucleoolivary projections into the inferior olive from the NIP. The x zone and the C2 zone both receive input from the contralateral medial accessory olive (MAO), both zones project into the NIP, and the NIP projects into those regions of the MAO which, in turn, project to these respective cortical zones and into the NIP. This suggest that the x zone is a component of the NIP-MAO circuit. Furthermore the proposed function of the x zone would support the view that this sagittal strip may have a more extensive rostrocaudal distribution in primates as compared to the cat.

The GABAergic cerebello-olivary projection in the rat

Immunocytochemical detection of glutamate decarboxylase (GAD), the predominant biosynthetic enzyme of gamma-aminobutyric acid (GABA), reveals the presence of a dense GABAergic innervation in all parts of the inferior olive. One brain center that provides a substantial projection to the inferior olive is the cerebellar nuclei, which contain many small GABAergic neurons. These neurons were tested as a source of GABAergic olivary afferents by combining retrograde tract tracing with GAD immunocytochemistry. As expected from previous studies, injections of wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) into the inferior olive retrogradely label many small neurons in the interposed and lateral cerebellar nuclei and the dorsal part of the lateral vestibular nucleus, and fewer neurons in the ventro-lateral region of the medial cerebellar nucleus. These projections are predominantly crossed and are topographically arranged. The vast majority, if not all, of these projection neurons are also GAD-positive. The relative contribution of this projection to the GABAergic innervation of the inferior olive was tested by lesion of the cerebellar nuclei, or the superior cerebellar peduncle. Within 10 days the lesion eliminates most GAD-immunoreactive boutons in the principal olive, the rostral lamella of the medial accessory olive, the ventrolateral outgrowth, and the lateral part of the dorsal accessory olive ventral fold. Thus, the effectiveness of this depletion demonstrates that the cerebellar nuclei provide most of the GABAergic innervation to regions of the inferior olive known to receive a cerebellar projection. Moreover, when the lateral vestibular nucleus is damaged, the dorsal fold of the dorsal accessory olive is depleted of GABAergic boutons. The synaptic relations that boutons of the GABAergic cerebello-olivary projection share with olivary neurons were investigated at the electron microscopic level by GAD-immunocytochemistry, anterograde degeneration of the cerebellar axons or anterograde transport of WGA-HRP. All of these methods confirm that GABAergic, cerebello-olivary axon terminals contain pleomorphic vesicles, and synapse on various portions of olivary neurons, and especially on dendritic spines within glomeruli, often in very close proximity to the gap junctions that characteristically couple the dendritic profiles. These results demonstrate four major points: that virtually all of the GABAergic, and presumably inhibitory, neurons of the cerebellar and dorsal lateral vestibular nuclei are projection neurons; that a large portion of the inferior olive receives GABAergic afferents from the cerebellar nuclei; that a portion of the dorsal accessory olive receives GABAergic afferents from the dorsal lateral vestibular nucleus; and that cerebello-olivary fibers often synapse near gap junctions, and therefore could influence electrical coupling of olivary neurons.

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)

Medial cerebellum and long-term habituation of acoustic startle in rats.

Three experiments assessed the effects of damage to the medial cerebellum on long-term habituation (LTH) of the acoustic startle response. Experiment 1 replicated previous results. Lesions of the cerebellar vermis blocked LTH without affecting initial response levels or short-term habituation (STH). The lesions did not disrupt LTH of a simultaneously measured lick-suppression response. In Experiment 2, vermal lesions again blocked LTH of acoustic startle. Control lesions of the cerebellar hemispheres did not affect LTH. In Experiment 3, lesions to the medial (fastigial) cerebellar nuclei blocked LTH. Lesions to the lateral (dentate and interpositus) nuclei did not affect LTH. It is concluded that the medial cerebellum (cortex and nuclei) is part of the essential circuitry for LTH of acoustic startle, whereas the lateral cerebellum is not involved in the basic habituation process.

Neuronal connections between the cerebellar nuclei and hypothalamus in Macaca fascicularis: Cerebello‐visceral circuits

The purpose of this study was to identify the basic pattern of interconnections between the cerebellar nuclei and hypothalamus in Macaca fascicularis. The distribution of retrogradely labeled cells and anterogradely filled cerebellofugal axons in the hypothalamus of M. fascicularis was investigated after pressure injections of a horseradish peroxidase mixture (HRP + WGA-HRP) in the cerebellar nuclei. Following injections in the lateral, anterior, and posterior interposed cerebellar nuclei retrogradely labeled cells were present in the following areas (greatest to least concentration): lateral and dorsal hypothalamic areas, dorsomedial nucleus, griseum periventriculare hypothalami, supramammillary and tuberomammillary nuclei, posterior hypothalamic area, ventromedial nucleus and periventricular hypothalamus, around the medial mammillary nucleus, lateral mammillary nucleus, and infundibular nucleus. Cell labeling was bilateral with an ipsilateral preponderance. In these same experiments anterogradely labeled cerebellar efferent fibers terminated in the contralateral posterior, dorsal and lateral hypothalamic areas, and the dorsomedial nucleus. In these regions retrogradely labeled hypothalamic cells were occasionally found in areas that also contained anterogradely filled cerebellar axons. This suggests a partial reciprocity in this system. In addition, sparse numbers of labeled cerebellar fibers recross in the hypothalamus to distribute to homologous areas ipsilateral to the injection site. Subsequent to an injection in the medial cerebellar nucleus (NM), cell labeling was present in more rostral hypothalamic levels including the lateral and dorsal hypothalamic areas, the dorsomedial nucleus, around or in fascicles of the column of the fornix, and in the periventricular hypothalamic area. Although no fastigiohypothalamic fibers were seen in this study, on the basis of information available from the literature it is likely that such a connection exists in primates. In summary, hypothalamic projections to NM originated mainly from rostral to midhypothalamic levels, whereas those projections to the lateral three cerebellar nuclei came from mid and more caudal levels. The existence of direct hypothalamic projections to cerebellar nuclei in M. fascicularis and of cerebellofugal projection to some hypothalamic centers indicates that circuitry is present through which the cerebellum may influence visceral functions. Furthermore, the fact that projections to NM versus the other cerebellar nuclei originate from somewhat different regions of the hypothalamus would suggest that the visceral functions modulated by each pathway is not the same.

Cerebellar nucleo‐olivary projections in the rat: An anterograde tracing study with Phaseolus vulgaris‐leucoagglutinin (PHA‐L)

In order to evaluate the reciprocity of olivo-cerebellar and cerebello-olivary connections, a detailed description of the cerebellar nucleo-olivary projection in the rat is presented using small, iontophoretic injections of the anterograde tracer Phaseolus vulgaris-leucoagglutinin. Sparse projections were found to arise from the rostral part of the medial cerebellar nucleus toward the lateral part of the caudal medial accessory olive. Its medial parts receive a projection from the dorsolateral protuberance of the medial cerebellar nucleus. Caudal and lateral regions of the medial cerebellar nucleus project to the "beta" group and dorsomedial cell column. Heavy olivary projections to circumscribed parts of the inferior olive were found after injections in the remaining cerebellar nuclei. The medial part of the posterior interposed nucleus connects to caudolateral areas of the rostral half of the medial accessory olive, whereas lateral areas project to more rostromedial parts. The most ventromedial part of the lateral cerebellar nucleus projects to the ventrolateral outgrowth. Adjacent medial, ventral, and caudal regions connect to the ventral leaf of the principal olive. The cerebellar origin of the projection to its dorsal leaf is located in lateral, dorsal, and rostral parts of the lateral cerebellar nucleus. The dorsolateral hump projects to the dorsomedial group of the rat inferior olive. Rostromedial projections to the dorsal accessory olive originate from the lateral part of the anterior interposed nucleus, whereas its medial parts project to more lateral and caudal regions of this olivary subnucleus. The dorsal fold of the dorsal accessory olive does not receive a projection from the cerebellar nuclei but from the lateral vestibular nucleus. No cerebellar projections were found to the dorsal cap. Relatively strong ipsilateral projections, which were the mirror images of the contralateral projections, were observed in the dorsomedial group, rostral medial accessory olive, and ventral leaf of the principal olive. When both the inferior olive and the cerebellar nuclei are considered as folded but continuous sheets of grey matter, the complete nucleo-olivary projection can be described as a simple transformation.

Projections of the medial cerebellar nucleus to oculomotor‐related midbrain areas in the rat: An anterograde and retrograde HRP study

The mesencephalic projections of the medial cerebellar nucleus (MCN) were studied in the rat by using the method of anterograde transport of wheat germ agglutinin/horseradish peroxidase to establish connections of the nucleus with oculomotor-related nuclei as a basis for its proposed role in eye movement. The principal targets of projections were the supraoculomotor ventral periaqueductal gray (PAG) and lateral PAG, and paraoculomotor cell groups (nucleus of Darkschewitsch and medial accessory nucleus of Bechterew). Lesser projections were observed to the intermediate layer of the superior colliculus, nucleus of the posterior commissure, and prerubral field. Following transcannular HRP gel implants into the oculomotor complex that included adjacent paraoculomotor nuclei, the largest number of retrogradely labeled cells was found in the caudal MCN. The findings suggest that the caudal MCN in the rat, like the primate fastigial nucleus, is involved in the control of eye movement.

Topographic organization of the cerebellar nucleocortical projection in the albino rat: an autoradiographic orthograde study

The topography of the cerebellar nucleocortical projection was investigated in the albino rat by experiments employing an autoradiographic orthograde tracing method. The present results indicate that neurons in the deep cerebellar nuclei project to the granule cell layer of cerebellar cortex as mossy fiber terminals in an orderly way. Thus, the medial cerebellar nucleus projects mainly to the bilateral vermis with ipsilateral dominance. The interpositus and lateral cerebellar nuclei project mainly to the intermediate and lateral zones of the anterior and posterior lobes of the cortex, respectively. The paraflocculus and flocculus receive the nucleocortical projection from the caudal and ventral parts of the interpositus nuclei and the dentate nucleus. A mediolateral topography within each subdivision of the cerebellar nuclear complex was observed; the medial and lateral parts of the subdivision project to the more medial and lateral portions of the primary cortical targets of the subdivision, respectively.

Corticonuclear and corticovestibular projections from the uvula in the albino rat: differential projections from sublobuli of the uvula

The organization of the corticonuclear and corticovestibular projections from the uvula was investigated in the albino rat by an autoradiographic method. The corticonuclear fibers from sublobule a of the uvula terminated in the caudoventral part of the medial cerebellar nucleus, and the caudomedial part of the posterior interpositus nucleus with mediolateral topography. The medial and lateral portions of the sublobule projected to the medial cerebellar and posterior interpositus nuclei, respectively. The corticovestibular fibers from sublobule a terminated in the dorsal and rostral parts of the superior vestibular nucleus, the dorsal part of the lateral vestibular nucleus, and the caudomedial part of the spinal vestibular nucleus. However, the corticonuclear fibers from sublobuli b and c of the uvula terminated additionally in the ventromedial part of the lateral cerebellar nucleus, while the corticovestibular fibers from these sublobuli terminated additionally in the subnucleus y of the vestibular complex, with probable termination in the medial vestibular nucleus. The cortical region which sent efferent projections to the ventromedial part of the lateral cerebellar nucleus and the subnucleus y was located laterally in sublobuli b and c of the uvula. These differential projection patterns from the dorsal and ventral sublobuli suggest the difference of the functional correlates between the sublobuli in the uvula.

HRP study of cerebellar corticonuclear‐nucleocortical topography of the dorsal culminate lobule—lobule v—in a prosimian primate (Galago): with comments on nucleocortical cell types

The distribution of retrogradely labeled cerebellar nucleocortical (NC) cells and anterogradely labeled corticonuclear (CN) fibers was investigated in a prosimian primate (Galago) by means of horseradish peroxidase as a tracer. Iontophoretic and pressure injections were made in the cortex of lobule V and the resultant patterns of label were determined in the cerebellar nuclei. Following iontophoretic injections in vermal (zone A), intermediate (zones C1, C3), and lateral (zone D) cortices, retrogradely labeled cells were present in medial (NM), anterior interposed (NIA), and lateral (NL) cerebellar nuclei, respectively. Larger injections that involved A-C2 zones resulted in NC label in NM, medial NIA, and throughout the posterior interposed (NIP) nucleus. Retrogradely labeled NC cells were usually found in areas of their respective nuclei that also contained anterogradely filled CN axons. In addition, retrogradely labeled cells were seen contralateral to some injection. Contralateral NC cells were found mainly in the NM and NIP and seemed to be labeled in response to injections that involved zones A, C2, and possibly x on the opposite side. No contralateral CN labeling was seen. It appears that the NC projections of lobule V follows a basic zonal (sagittal) orientation and that most are reciprocal to CN fibers arising from the same cortical area. There is evidence of zonal heterogeneity in the ipsilateral NC projection. Iontophoretic injections placed in adjacent zones resulted in markedly different numbers of retrogradely labeled NC cells in their respective nuclei. Also, after pressure injections that involved two or more adjoining zones, the number of labeled NC cells was large in one nucleus but minimal in an adjacent nucleus. These data suggest that different cerebellar cortical zones have quantitatively different NC input; this may relate to specific functional demands placed on each nucleus and its corresponding cortical zone. On the basis of their known connections, it is hypothesized that there are at least three and possibly four categories of NC cells. Ipsilateral reciprocal NC cells are found in, or on the periphery of, CN terminal fields formed by axons originating from the same cortical area to which the NC cells project. Ipsilateral nonreciprocal NC cells are located outside the CN terminal field and may even be found in an adjacent nucleus; these are fewer in number than the reciprocal population. Contralateral NC cells are found in the opposite cerebellar nuclei and appear to be topographically related to the ipsilateral contingent as well as to the injection site.(ABSTRACT TRUNCATED AT 400 WORDS)

Topographic organization of the corticonuclear fibers from the tuber vermis and paramedian lobule in the albino rat.

The topographic organization of the corticonuclear fibers from the tuber vermis and paramedian lobule in the albino rat was investigated by autoradiographic anterograde tracing method. The medial portion of the tuber vermis projects to the dorsal part of the caudomedial subdivision of the medial cerebellar nucleus (MNcm), whereas the lateral portion of the tuber vermis projects to the dorsal part of the MNcm and the caudal part of the middle subdivision of the medial nucleus. The intermediate cortex of the paramedian lobule can be subdivided mediolaterally into three portions which project to the dorsolateral protuberance of the medial cerebellar nucleus, the rostrodorsal part of the posterior interpositus nucleus, and the caudodorsal part of the lateral anterior interpositus nucleus, respectively. The lateral cortex of the paramedian lobule can also be subdivided mediolaterally into two portions: the medial portion projects to the dorsolateral hump, and the lateral one to the lateral cerebellar nucleus. These results indicate that the cortical efferent fibers from the tuber vermis and paramedian lobule are clearly organized in the mediolateral direction in the albino rat.