The cerebellar nucleocortical projections in the rat. A retrograde labelling study using horseradish peroxidase combined to a lectin

Variations on the theme: focus on cerebellum and emotional processing

The cerebellum operates exploiting a complex modular organization and a unified computational algorithm adapted to different behavioral contexts. Recent observations suggest that the cerebellum is involved not just in motor but also in emotional and cognitive processing. It is therefore critical to identify the specific regional connectivity and microcircuit properties of the emotional cerebellum. Recent studies are highlighting the differential regional localization of genes, molecules, and synaptic mechanisms and microcircuit wiring. However, the impact of these regional differences is not fully understood and will require experimental investigation and computational modeling. This review focuses on the cellular and circuit underpinnings of the cerebellar role in emotion. And since emotion involves an integration of cognitive, somatomotor, and autonomic activity, we elaborate on the tradeoff between segregation and distribution of these three main functions in the cerebellum.

Cerebellar loops: a review of the nucleocortical pathway

Feedback pathways are a common circuit motif in vertebrate brains. Reciprocal interconnectivity is seen between the cerebral cortex and thalamus as well as between basal ganglia structures, for example. Here, we review the literature on the nucleocortical pathway, a feedback pathway from the cerebellar nuclei to the cerebellar cortex, which has been studied anatomically but has remained somewhat obscure. This review covers the work examining this pathway on a number of levels, ranging from its existence in numerous species, its organization within cerebellar circuits, its cellular composition, and a discussion of its potential roles in motor control. Recent interest in cerebellar modular organization raises the profile of this neglected cerebellar pathway, and it is hoped that this review will consolidate knowledge gained over several decades of research into a useful format, spurring new investigations into this evolutionarily conserved pathway.

Somatotopic nucleocortical projections to the multiple somatosensory cerebellar maps

The cerebellum is organized in a series of parasagittal compartments: in C1-C3 and C2 compartments Purkinje cells receive climbing fibre afferents from the rostral part of the accessory olives, and project their axon to the nucleus interpositus anterior and posterior, respectively. Within these compartments electrophysiological studies have shown that the cutaneous input carried by climbing fibre afferents is topographically organized so as to design a map of peripheral body districts. The body map is replicated over the anterior lobe-pars intermedia and the paramedian lobule, and anatomical studies have indicated that the replication is partly due to the axonal branching of olivocerebellar neurons. The aim of this study was to analyse the presence of a somatotopic organization and of a branching pattern in the nucleocortical projections, in relation to the replicated body maps within C1-C3 and C2 compartments. By using double retrograde neuronal tracing we explored, in the cat, the topographic distribution of single- and double-labelled cells in the interposed nuclear subdivisions, after tracer injections into forelimb or hindlimb regions of the anterior lobe-pars intermedia, paramedian lobule and hemisphere (medial crus II). Most of the nucleocortical neurons were found in ipsilateral nucleus interpositus posterior, with smaller numbers in the ipsilateral nucleus interpositus anterior. Nucleocortical neurons projecting to forelimb- or hindlimb-related areas are completely segregated, the forelimb neurons being located laterally and the hindlimb neurons medially in the nucleus interpositus posterior. Within their respective domains both the forelimb and hindlimb populations projecting to the anterior lobe-pars intermedia are partly segregated from those projecting to the paramedian lobule, in that the two populations are slightly shifted along the dorsoventral axis of the nucleus. Although mostly different, some of the cells are common to the two forelimb populations, since they send axonal branches to the homologous areas of the anterior lobe and paramedian lobule. Contralateral fastigial or interposed nucleocortical projections are restricted to the anterior lobe-pars intermedia, and their neurons of origin are different from those that project to the ipsilateral cerebellar cortex: i.e. they are not a bilateral, but a separate contralateral component.

Cerebellar corticonuclear and nucleocortical projections in the vermis of posterior lobe of the rat as studied with anterograde and retrograde transport of WGA-HRP

Corticonuclear (CN) and nucleocortical (NC) projections of the cerebellum were studied in rats by using antero- and retrograde transport of wheatgerm agglutinin-conjugated horseradish peroxidase (WGA-HRP). Following minute injections of WGA-HRP in different folia for vermal lobules VI-VIII, a rostrocaudal topography was observed in the CN projection; lobules VIa and VIb, c projected to distinctly separate areas in the ipsilateral fastigial nucleus (FN): VIa projected to the ventral part of the medial subdivision of the FN (FNm), whereas VIb, c projected to the dorsocaudal part of the caudomedial subdivision of the FN (FNcm) and to the caudal FNm. The terminals from lobules VIb, c and VII occupied partially overlapping areas in the caudal part of the ipsilateral FNcm and FNm. A few terminal fibers were also seen in the dorsolateral protuberance of the FN (dlp). The fibers from vermal lobule VIII terminated in the ipsilateral rostral FNcm and in the FNm. The latter terminal area was divided into two parts: a smaller dorsal and a larger ventral part that in turn overlapped almost completely with the terminal area of fibers from lobule VIa. Retrogradely labeled fastigial neurons were found in the areas of the FN where Purkinje-cell (P-cell) axons from the respective injection sites terminated. In addition, retrogradely labeled fastigial neurons were scattered in areas outside the P-cell terminal fields on the injection side and in the contralateral FN.

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.

Anatomical mapping of the cerebellar nucleocortical projections in the rat: a retrograde labeling study

An analysis of the cerebellar nucleocortical projections was made by means of retrograde cellular labeling with wheat germ agglutinin-horseradish peroxidase conjugate. Each of the main nuclear subregions appears to give rise to nucleocortical projections. The cortical distribution of the projections is referred to here in term of sagittal zones. Zones A, B, and C conform to the recent description in the rat (Buisseret-Delmas, '88a,b) on the basis of their olivocortical and corticonuclear projections. A corresponding description of zone D is given here. According to their distribution, three types of nucleocortical projections have been distinguished: 1) ipsilateral, reciprocal; 2) nonreciprocal; and 3) contralateral, symmetrical to the corticonuclear afferent. Reciprocal projections are strictly arranged in the sagittal direction, with the following zonal distribution. Zone A is subdivided into two subzones. Medial A zone receives its nuclear afferents from the medial aspect of the nucleus medialis (NM). The lateral A zone of the anterior lobe and lobule VI and that of the posterior lobe receive their reciprocal nuclear afferents from the ventrolateral NM and the dorsolateral protuberance, respectively. Zone B does not seem to receive nucleocortical projections. Zone C has three subzones in the rat. C1 is supplied from the medial third of the anterior and posterior subdivisions of the nucleus interpositus (NIA and NIP, respectively). C2 is supplied from the central third of the NIA and NIP. Rostrocaudally, the anterior lobe and lobule VIII are connected to the NIA, and lobules VI and VII to the NIP. C3 appears to be connected to the lateral third of NIA. Zone D contains three subzones mediolaterally in the rat. D0, not previously described, is defined on the basis of both its olivary afferent from the medial half of the ventral lamella of the principal olive and its corticonuclear projections onto the dorsolateral hump of Goodman et al. ('63). It receives a reciprocal nucleocortical afferent from the dorsolateral hump. D1 receives its olivary afferent from the dorsal lamella of the principal olive. It is reciprocally connected with the lateral, magnocellular part of the nucleus lateralis (NL). D2 is the most lateral subzone of the hemisphere. Its olivary afferent comes from the lateral half of the ventral lamella of the principal olive. D2 is reciprocally connected with the ventral, parvicellular subdivision of NL. The main cortical recipients for the nonreciprocal projections are the lateral A zone, the C3, and the D1 subzones.(ABSTRACT TRUNCATED AT 250 WORDS)

The GABAergic neurones of the cerebellar nuclei in the rat: projections to the cerebellar cortex

The presence of gamma-aminobutyric acid (GABA) in the neurones of the cerebellar nucleocortical pathway is here reported. The pathway was identified by retrograde tracer and the GABA content was revealed immunohistochemically. It was found that most of the neurones giving rise to the reciprocal, non-reciprocal and symmetrical projections are indeed GABA-immunoreactive. They were observed in all the subdivisions of the nucleus medialis, of the nucleus interpositus and of the nucleus lateralis sending axons respectively to the sagittal zones A, C1-3 and D of the cerebellar cortex. The nucleus vestibularis lateralis and the related sagittal zone B were devoid of such projections.

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)