Fastigiovestibular projections in the rat: retrograde tracing coupled with gammaamino-butyric acid and glutamate immunohistochemistry.

In this study, a double labeling technique using retrograde tracing with protein-gold complex (gold-HRP) in conjunction with a gammaamino-butyric acid (GABA) and glutamate immunohistochemical procedure was performed to identify GABA (GABA-IR) and glutamate (Glu-IR) immunoreactive neurons in the cerebellar fastigial nucleus (FN) that projects to the vestibular nuclei (VN). The results show that FN neurons projecting to the VN consist of both GABA-IR and Glu-IR neurons with a predominance of glutamatergic ones. Because GABAergic neurons in the cerebellar nuclei project to the inferior olive (IO), double retrograde labeling experiments were performed with injections of gold-HRP in the IO and of biotilynated dextran amine in the VN. This showed that the GABA-IR fastigiovestibular neurons project by axon collaterals to both the VN and the IO.

Dentatovestibular projections in the rat.

The dentatovestibular connections were investigated using anterograde and retrograde tracing methods. All parts of the cerebellar nucleus lateralis (NL) or dentate nucleus sent fibers onto the ipsilateral vestibular nuclear complex. In spite of their apparently widespread area of termination, dentatovestibular fibers were distributed differentially, according to the subregion of the NL they arose from. Fibers from the main, magnocellular region and the dorsolateral hump (dlh) reached the four main vestibular nuclei, but preferentially the superior (SV) and inferior (IV) vestibular nuclei. The projections to the lateral and the medial vestibular nuclei, which were less abundant, essentially originated from neurons located in the dlh. Fibers arising from the parvocellular subregion of Flood and Jansen terminated within the SV and IV only. Some rare reciprocal vestibulodentate projections were observed. These observations suggest highly integrated activities of dentatovestibular connections related to postural, but also vestibulo-oculomotor functions.

Brainstem efferents from the interface between the nucleus medialis and the nucleus interpositus in the rat.

In a previous report (Buisseret-Delmas et al. [1993] Neurosci. Res. 16:195-207), the authors identified the interface between the cerebellar nuclei medialis and interpositus as the origin of the nuclear output from cortical zone X. They named this nuclear interface the interstitial cell group (icg). In this study, the authors analyzed the icg efferents to the brainstem by using the anterograde and retrograde tracer biotinylated dextran amine. The main targets of these efferents are from rostral to caudal: 1) the accessory oculomotor nuclear region, essentially, the interstitial nucleus of Cajal; 2) the caudoventral region of the red nucleus; 3) a dorsal zone of the nucleus reticularis tegmenti pontis; 4) restricted regions of the four main vestibular nuclei; and 5) three restricted areas in the inferior olive, one that is caudal in the medial accessory subnucleus and two others that are rostral and caudal in the dorsal accessory subnucleus, respectively. These data support the notion that the icg contributes to the control of gaze-orientation mechanisms, particularly those that are related to the vestibuloocular reflex.

Connections between the cerebellar nucleus interpositus and the vestibular nuclei: an anatomical study in the rat.

Interposito-vestibular connections were analysed, using the anterograde and retrograde tracer biotinylated dextran amine. The interposito-vestibular projections mainly arise from medial portions of the cerebellar nuclei interpositi anterior (NIA) and posterior (NIP), and reach each of the main vestibular nuclei, ipsilaterally. The highest density of projections is found throughout nucleus vestibularis lateralis. Fibres also reach the peripheral part of nucleus superior, the caudal part of nucleus inferior, and the lateral part of nucleus medialis. Some fibres also reach groups I, x and f. Contralaterally, few fibres reach zones of the vestibular nuclei symmetric to the ipsilateral projection. A small, reciprocal, vestibulo-interposed projection is sent from the vestibular nuclei onto NIA-NIP. Possible influences of the interposito-vestibular projections upon the major targets of the vestibular nuclei, spinal motoneurones and oculomotor neurones, are discussed.

Synaptic connections of Purkinje cell axons with nucleocortical neurones in the cerebellar medial nucleus of the rat.

The cerebellar nucleocortical neurones may be part of a cortico-nucleocortical loop. It has not yet been demonstrated, however, whether they are directly afferented by Purkinje cell axons. This question has been addressed by using electron microscopic methods. WGA-HRP injections into the cerebellar vermis anterogradely labelled Purkinje cell terminals and retrogradely labelled nucleocortical neurones of the nucleus medialis. Postembedding GABA immunolabelling was used to double-labelled PC terminals and identified the GABA-immunoreactive nuclear neurones. Of the identified nucleocortical neurones, the majority were immunonegative, but a few were GABA-immunoreactive. Both types were in synaptic contact with identified Purkinje cell terminals.

Nucleus medialis-nucleus interpositus interface: its olivary and cerebellocortical projections in the rat.

The nuclear target of the X zone of the cerebellar cortex was identified in rats as clusters of neurons scattered at the interface between the nuclei medialis (NM) and interpositus (NI). In a previous study, we had outlined these target neurons and termed them "interstitial cell groups" (icg). In order to determine whether the icg should be considered as part of either the NM or the medial NI, we analyzed two efferent pathways from the icg: their nucleocortical and nucleoolivary projections. These were compared to their homologues from the NM and the NI. This analysis is based on mapping retrograde cell labeling and anterograde terminal labeling following microinjections of tracers in either the cerebellar cortex, the cerebellar nuclei, or the inferior olive. Nucleocortical projections originating from the icg are of the three types described previously: a "reciprocal" projection to the ipsilateral X zone, a "nonreciprocal" projection to the ipsilateral A zone, and a "symmetrical" projection to the contralateral X zone. These features can be considered as the summed characteristics of the nucleocortical projections from the NM and from the medial NI. Nucleoolivary projections from the icg target the lateral-rostral portion of the dorsal accessory olive as well as the centrocaudal part of the medial accessory olive. These pathways converge with the nucleoolivary projections from the medial NI and from the NM, respectively. The icg receives olivary afferents from both the regions of the dorsal and medial accessory olives to which it projects. On the basis of similarities shown here between the two types of efferents originating from the icg and those from the NM as well as the medial NI, the icg may be regarded as a "mosaic" of neuron clusters alternately belonging to the NM and the medial NI. Therefore, the icg would be reciprocally connected with the inferior olive.

On the caudal extension of the X zone in the cerebellar cortex of the rat.

Following a selective injection of biotinylated dextran amine in the nuclear target (the interstitial cell groups, icg) of the X zone of the rat cerebellum, retrogradely labelled Purkinje cells (PCs) were found within a longitudinal strip of cortex, 250 microns in width, 1000 microns lateral to midline. This labelling delineates two compartments in the X zone, one rostral through lobules II-VI, and one caudal through lobules VIII-X. The whole rostrocaudal extent of the icg appears to be the target of PCs from both compartments without any apparent topographical organization.

The projection from the primary motor and somatic sensory cortex to the basilar pontine nuclei. A detailed electrophysiological and anatomical study in the rat.

The projections from the primary motor and somatic sensory cortex onto the basilar pontine grey were studied in Wistar Rats injecting microvolumes of WGA-HRP solution in sites of the motor and sensory cortex electrophysiologically identified. The main results may be summarized as follows. (a) The projections from both the motor and sensory cortex were found as rostrocaudally oriented columns of terminals in the basilar pontine nuclei. The projection from the motor cortex extended to all over the rostrocaudal extension of the basilar pontine nuclei. To a rostrocaudal shift of the pontine projection field correspond a rostrocaudal displacement in the motor area. The projection from the sensory cortex was mainly restricted to the caudal two thirds of the basilar pontine nuclei, though the hindlimb region of the sensory cortex also showed a discrete representation in the rostral third of the basilar pontine nuclei. (b) The terminal fields of the motor and sensory cortex were segregated except those in the caudal pontine level, which come from the projection of the hindlimb cortical regions. (c) Within the terminal fields of the projections from the motor as well as from the sensory cortex a clearcut topographical arrangement was observed between the projections of cortical areas controlling the head, the forelimb and the hindlimb regions. (d) Within the location of these major subdivisions, the representations of individual body segments were overlapped for a little part ("convergent zones"), whereas the greater part of their projection zones was selective of each cortical field ("private zones"). In conclusion, the present study showed that the projections from the motor and sensory cortex to the basilar pontine nuclei are arranged with a very precise somatotopical organization.

[Anatomo-functional organization of the neocerebellar control pathways on the cerebral motor cortex]. / Organisation anatomo-fonctionnelle de la voie d'influence du néocervelet sur le cortex cérébral moteur.

In a first phase of this study, the topographic arrangement of the dentato-thalamocortical projections was analyzed anatomically in albinos rats, by using anterograde and retrograde tracing methods. By applying intracortical microstimuli through the cerebral motor cortex prior to each microinjection of the tracer, the motor function of each injected cortical site was defined. As a consequence of the precise topographic arrangement of the dentato-thalamocortical pathways, we infer a somatotopic motor organization within the three cytoarchitectonic subdivisions of the cerebellar nucleus lateralis (NL), which corresponds to the dentate nucleus of the primate cerebellum: the hindlimb would be poorly represented, rostrally, whereas the head and forelimb would be more widely represented, within the central and caudal parts of the NL. In the second phase, the motor responses to direct microstimulations through the NL were mapped. The results confirmed the anatomofunctional arrangement deduced from the observations made in the first part of the study. The principles of the functional organization of the NL were also defined: i) the synergistic character of the movements induced by dentate stimulation is reflected by the activation of agonist as well as antagonist muscles that combine to move a particular segment of the body; ii) some body segments (e.g. those of the hindlimb) are represented within only one subdivision of the NL (single representation); others, such as the axio-proximal segments of the body, can be activated in a similar way from sites located in two or three subdivisions (multiple representation); finally, distal segments (digits or vibrissae) are multiply represented but activated in different ways by their various representation sites (specific representation): they can be moved independently from the parvocellular subdivision and only synchronously from their other representation site. The parvocellular subdivision of the rat NL is proposed as an equivalent to the "neodentatum" of the primate cerebellum.

The X zone and CX subzone of the cerebellum in the rat.

The existence of an X zone (lateral to the A zone) and a CX subzone (lateral to the C1 subzone) was documented within the anterior lobe and lobule VI in cats and primates. On the basis of their respective efferent and climbing fibre (CF) afferent connections, delineation of these two cortical subdivisions has been investigated here, in the rat, using small injections of WGA-HRP in the cerebellar cortex. We observe that both X and CX are "fractured" into a rostral and a caudal compartment. The rostral compartment of the X zone extends over lobules IV, V and VI and its caudal compartment over lobules VIII, IX and X. The rostral compartment of the CX subzone seems to be restricted to lobules V and VI, its caudal compartment cannot be topographically distinguished, over lobules IX and X, from the caudal compartment of the X zone. The olivary afferents to the X zone and the CX subzone arise from the horizontal and vertical lamellae of the medial accessory olive: subnucleus a projects into the rostral compartment and lobule VIII of the X zone. Subnuclei b and c project into the rostral compartment of both X and CX. The dorsomedial cell column selectively projects onto the caudal compartment of both X and CX over the vestibulo-cerebellum. The corticonuclear projections of the X zone have been found within the junctional region between the nucleus medialis and the nucleus interpositus (NI), here defined as the interstitial cell groups (icg), the corticonuclear projections of the CX subzone within the medial NI. It is suggested that the icg correspond to clusters of neurones dissociated from the medial aspect of the NI. We therefore consider the X zone and CX subzone of the rat, on the basis of their corticonuclear efferents, as "medial C1" and "lateral C1" subzone, respectively, although both may be regarded as part of the A zone on the basis of their olivary afferents.

Multiple representation in the nucleus lateralis of the cerebellum: an electrophysiologic study in the rat.

The motor organization of the nucleus lateralis (NL) of the rat's cerebellum was investigated by observing the motor effects of electrical microstimulations of the NL. The movements evoked by the NL mainly concerned forelimb and head segments. Only in a few cases were movements of hindlimb segments evoked. Motor effects were obtained according to a precise topographical pattern. This pattern delimited functional zones, or representations, within the NL, each zone being specifically related to a particular segment of the body. A few body segments were activated from single zones only (single representation) whereas some other body segments could be activated from different zones of the NL. Among them, the axio-proximal body segments were activated in a similar way from all sites (multiple representation) whereas the distal body segments were differently activated from the various representation zones (specific representation). The multiple and specific representations were distributed between the 3 cytoarchitectonic subregions of the NL (NLm, DLH and slp) in such a way that the body segments were usually represented only once in each individual NL subregion. Each NL subregion included sets of representations concerning body segments characterized by a topographical continuity (e.g. the different segments of the forelimb in both DLH and slp). Thus, the individual NL subregions may bring into play coordinate plurisegmental muscular activities of the limbs and/or of the head. The NLm controls movements of all the segments of the head and those of axio-proximal segments of both limbs. The DLH particularly controls movements of the head, including both the proximal (neck) and the oral regions. To a lesser degree, DLH controls movements of the various segments of the forelimb, including synchronous flexion of all the digits. The slp is specifically involved in the control of motor activities of: i) the proximal segment of the head (rotation of the neck) as well as its distal segments (displacement of individual vibrissae, rotation of the ear pinna) and ii) the various segments of the forelimb including individual digits. Functionally, the proximal segments would be concerned in the spatial displacement of the limbs or of the head whereas the distal segments would be involved in the realization of precise and discrete movements related to specific functions of the distal segments concerned. The 3 subregions of the NL may be concerned in different motor functions.(ABSTRACT TRUNCATED AT 400 WORDS)

Dentate control pathways of cortical motor activity. Anatomical and physiological studies in rat: comparative considerations.

The dentato-thalamocortical projections have been studied in albino rats using anatomical and physiological approaches. The anatomical analysis reveals that the dentatothalamic input to the ventral thalamus and the thalamocortical projection from this region onto the motor cortical area have a complex topographical arrangement. The corticothalamic reverberating pathways, both direct and through a relay in the nucleus reticularis thalami, are also roughly arranged in register with the same topographical pattern. This arrangement has been reconciled with that of the motor cortex, as determined by the motor effects of intracortical microstimulations. From this is inferred a somatotopical arrangement of the cerebellar nucleus lateralis, or dentate. These observations are confirmed by the results of our physiological analysis. The movements obtained with direct microstimulations of the nucleus lateralis affect either one joint (simple movements) or, more seldom, several joints (complex movements) of the same limb. A rough rostrocaudal arrangement is found in the nucleus lateralis: the caudocentral regions of the nucleus contain the representation of the musculature of forelimb and head, whereas the hindlimb is represented in the rostralmost part of the nucleus. A more complex organization is found to be related to the three cytoarchitectonic subdivisions of the nucleus lateralis. The main, large-celled part of the nucleus is engaged in the control of the large skeletal musculature. The dorsolateral hump is involved in mouth and peri-oral activities. The ventral, parvocellular, subnucleus is involved in fine exploratory movements of vibrissae, eyes, and forelimb wrist and fingers. The implication of the dentato-thalamocortical pathways in the cortical motor activities in the rat is discussed with attention to the dentate control of the "voluntary" motricity in primates.

Functional organization of the direct and indirect projection via the reticularis thalami nuclear complex from the motor cortex to the thalamic nucleus ventralis lateralis.

The projection systems which arise from the motor cortex to reach the nucleus ventralis lateralis (VL) were investigated in the rat. They included a direct as well as an indirect projection via the reticularis thalami nuclear complex (RT). The investigation was performed in two steps: i) the former concerned the projection to the VL as well as to the RT from individual cortical foci electrophysiologically identified by the motor effects evoked by electrical stimulation; the second step concerned the projection from the RT to functionally defined regions of the VL. The direct projection from the motor cortex to the VL is somatotopically arranged. The projection reciprocates the fiber system directed from the VL to the motor cortex. Thus cortical zones controlling the motor activity of the proximal segments of the limbs project onto the regions of the VL that project back to these same cortical areas. With regard to cortical zones controlling the motor activity of the distal segments of the limbs, they not only project to the region of the VL specifically related to them, but also to the region of the VL associated with the cortical areas responsible for movements of the proximal parts of the same limb. In that case fiber terminals were more dense in the VL region controlling the proximal segment than in the region controlling the distal segment of the same limb. This organization suggests that proximal adjustments may be automatically provided by the motor activity of the distal segments of the same limb. The motor cortex projects to the rostral region of the RT with a precise topographical organization. In particular, the projection shows a dorsoventral organization in the RT in relation to the caudorostral body representation in the motor cortex. The projection which arises from the rostral region of the RT also reaches the VL with a topographical arrangement. It discloses a rostrocaudal organization in the VL in relation to a dorsoventral displacement in the RT. Comparing the projection from the motor cortex to the RT and that from this nuclear complex to the VL it was shown that the regions of the VL and their receptive cortical areas were associated with the same regions of the RT. It was therefore concluded that the motor cortical projection to the VL relayed by the RT is somatotopically organized. In both direct and relayed pathways the projections from "hind-" and "forelimb" motor area are segregated, whereas the "head" projection overlaps, at least partially, the "forelimb" terminal field.(ABSTRACT TRUNCATED AT 400 WORDS)

Sagittal organisation of the olivocerebellonuclear pathway in the rat. III. Connections with the nucleus dentatus.

The organization of olivary afferents and nuclear efferents of the D-zone of the rat cerebellum was studied by means of tracing with wheat-germ agglutinin-coupled peroxidase using tetramethylbenzidine as a chromagen. The tracer was injected iontophoretically within the cerebellar cortex. This allowed us to study both afferent and efferent pathways of the cerebellar lobules concerned with retrograde and anterograde tracing, respectively. Retrograde cellular labelling in the inferior olive was restricted to the principal olive (PO). Anterograde terminal labelling was found only within the various subdivisions of the nucleus lateralis or dentatus (ND). For any one of our small cortical injections there was a corresponding sagittal band of retrogradely labelled cells in the contralateral PO, and a sagittal band of terminal labelling through the ND. Based on both their olivary and nuclear connections, 3 sagittal subzones can be distinguished within the D-zone of the rat. From medial to lateral, we call them D0, D1 and D2. The 3 subzones run through part of the anterior and posterior lobes. D1 and D2 run continuously from their rostral to their caudal extents whereas D0 is discontinuous. It is interrupted through lobule VIc (crus I). The olivary projections to D0 arise within the medial half of the ventral lamella of the PO, including the dorsomedial cell column. Those to D1 arise within the dorsal lamella of the PO. Those to D2 arise within the lateral half of the ventral lamella of the PO. Rostrocaudally, widely distant cells of the same subdivision of the PO project to the same cerebellar lobule. This indicates extensive convergence of the olivary afferents within each of the 3 hemispheric compartments, D0, D1 and D2. Each of the 3 hemispheric subzones specifically projects to one of the 3 subdivisions distinguished within the ND of the rat, without apparent mediolateral overlapping. The medialmost D0 projects onto the dorsolateral hump; D1 projects more laterally onto the main, magnocellular part of the ND, and D2 projects ventrally onto the parvicellular subdivision of the ND. Thus the sagittal partition of the hemispheric cortex is reflected at the nuclear level. In contrast, Purkinje cell axons from individual lobules appear to branch extensively in the rostrocaudal direction. Therefore, within each of the 3 compartments D0, D1 as well as D2, the nuclear projection of the anterior lobe and the posterior lobe are largely coextensive.

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)

Neocerebellar control of the motor activity: experimental analysis in the rat. Comparative aspects.

The results collected by electrical microstimulation of the nucleus lateralis of the cerebellum in anaesthetized rats may be summarized as follows. The stimulations evoked motor effects in head and forelimb principally whereas hindlimb was only occasionally involved. The movements were prevalently segregated to only one joint (simple movements), in a lesser degree they involved two or three segments (complex movements). Simple and complex movements were apparently distributed in the nuclear mass without topographical segregation or preferentiality. The electromyographic records suggest that the neocerebellar movements are of synergistic nature. A somatotopical organization was evidenced within the nucleus lateralis: 3 specific functional regions were identified in the caudorostral nuclear extension. They concern the forelimb (caudally), head (centrally) and hindlimb (rostrally). This somatotopical organization persisted unmodified following elimination of either the cerebral motor cortex alone or in addition to that of the red nucleus. The nuclear subdivisions of the cerebellar nucleus lateralis showed functional differences: (1) the dorsolateral hump of Goodman et al. was principally involved in lip movements; (2) the subnucleus lateralis parvocellularis elicited movements of single vibrissae, neck and medio-distal segments of the forelimb, prevalently; (3) the magnocellular subdivision essentially controlled both limbs with large prevalence for their medio-proximal segments. To identify the functional role of the different descending pathways which relay the neocerebellum to the cord, the motor effects evoked in intact rats were compared with those elicited in rats submitted to cortical ablation and/or to lesion of the red nucleus region. The integrity of the cerebral cortex was essential only for distalmost forelimb motor activities. After lesion of the rubral region (which concomitantly eliminates corticospinal output), the stimulation of the nucleus lateralis evoked motor effects of the proximo-axial segments prevalently with intensity thresholds increased above two-fold those obtained in intact/decorticated rats. The movements elicited in rats with injury of the red nucleus region, including the ascending fibers of the brachium conjunctivum, are presumably mediated to the spinal cord through the reticulospinal pathway. The proportion of simple and complex movements decreased and increased respectively after cortical ablation and further on after injury of the red nucleus region. The discussion on the motor effects elicited in rats by the neocerebellum focussed on the possible role of 3 descending pathways.(ABSTRACT TRUNCATED AT 400 WORDS)

Synaptology of the cerebello-olivary pathway. Double labelling with anterograde axonal tracing and GABA immunocytochemistry in the rat.

The dentato-olivary projection has been ultrastructurally studied in rats that received a wheatgerm agglutinin-horseradish peroxidase (WGA-HRP) injection in the nucleus lateralis. Ultrathin sections containing the inferior olive have been double-labelled with the GABA-immunogold method. About 97% of the WGA-HRP labelled axon terminals are GABA-immunopositive. Most of them belong to a single type consisting of small boutons establishing symmetrical synapses on dendrites. Nevertheless, there is some morphological and neurochemical diversity among the labelled terminals, and particularly, a small contingent are GABA-immunonegative. Of the GABAergic dentato-olivary boutons, 4% occupy a privileged position, with synaptic contacts straddling two dendritic profiles linked by gap junctions. The strategic location of these inhibitory dentato-olivary synapses suggests that they can modulate the electrotonic coupling rate between sets of inferior olivary neurons.

Topographic organization of the interpositorubral connections in the rat. A WGA-HRP study.

The projections from the anterior (NIA) and posterior (NIP) interposed nuclei to the magnocellular red nucleus (RNm) have been investigated in the rat, using the retrograde transport of horseradish peroxidase-wheatgerm agglutinin conjugate. Projections from the NIA extend throughout the RNm, whereas those from the NIP only reach its medial aspect. In addition, a topographical organization of the NIA-RNm pathway was found, such that the medial NIA projects ventrally, the lateral NIA projects dorsally.

The dentatorubral projection in the rat: an autoradiographic study.

The dentatorubral projection has been mapped in rats using autoradiography. Any part of lateral cerebellar nucleus (NL) projects throughout the contralateral parvocellular red nucleus (NRp) rostrocaudally; the projection is topographically organized: (1) a caudorostral shift in the NL corresponds to a dorsoventral displacement through the NRp; matching of this arrangement with the origin of rubrospinal projections is discussed; (2) only ventral parts of the NL, including the parvocellar subnucleus, project to the lateral edge of the NRp.