The longitudinal zonal pattern in the paramedian lobule of the cat's cerebellum: an analysis based on a correlation of recent HRP data with results of studies with other methods.

In a preceding study of the distribution of retrogradely labeled cells in the inferior olive of the cat after microinjections of horseradish peroxidase (HRP) in the contralateral paramedian lobule (Brodal and Walberg, '77b), three longitudinal zones were distinguished. The zones were assumed to correspond to Voogd's zones C1, C2 and D, receiving their afferents from parts of the dorsal accessory olive, of the medial accessory olive and of the dorsal lamella of the principal olive, respectively. Labeled cells were not found in the ventral lamella of the principal olive, however, although there is no doubt that also this projects to the paramedian lobule. In the present study, iontophoretic ejections, covering the extreme lateral part of the paramedian lobule, gave rise to labeling of cells in the ventral lamella. It is concluded that the zone D in the paramedian lobule can be subdivided into two, a lateral, D2, and a medial, D1, receiving fibers from the ventral and dorsal lamella, respectively. Neither zone extends throughout the entire length of the paramedian lobule. Both are lacking most rostrally and most caudally. This and other findings prompted a renewed analysis of the entire pattern of zonal representation in the paramedian lobule, based on correlations of our observations with the HRP method with data obtained with other methods. The results of this analysis are briefly described and summarized in a diagram (fig. 3B). It is particularly remarkable that zone B is present in some folia medially. A somatotopical arrangement appears to be present within all zones. A full account and documentation will be presented separately (Brodal and Kawamura, '80).

The olivocerebellar projection in the cat studied with the method of retrograde axonal transport of horseradish peroxidase. IV. The projection to the anterior lobe.

Following injections of horseradish peroxidase (HRP) in the cerebellar cortex of the anterior lobe of the cat, the distribution of labeled cells in the inferior olive was mapped. The findings largely confirm those made previously in studies of olivary retrograde cell loss following cerebellar ablations (Brodal, '40b). In addition, they reveal further olivary areas projecting onto the anterior lobe, and permit a more detailed analysis of the pattern in this projection. Concerning major points the results are in agreement with physiological studies by Armstrong et al. ('74). They bring supporting evidence for a longitudinal zonal pattern in the anterior lobe (fig. 6C). The middle zone of the vermis receives its fibers from a large central area in the caudal half of the medial accessory olive, a lateral zone of the vermis from the lateral half of the dorsal accessory olive. Both olivary areas project to the corresponding cerebellar zone throughout lobules V-I. The lateralmost part of the anterior lobe (lobules IV-V) receives afferents from an area in the dorsal lamella of the principal olive. The intermediate part of lobules IV-V receives afferents from the medial half of the dorsal accessory olive and from an area in the rostral half of the medial accessory olive. There is suggestive evidence that the latter projects to a middle zone, the former to a medial and a lateral zone within the intermediate part as found physiologically. Conclusions concerning projections to the intermediate part of lobules III-II could not be made. The findings in this and preceding studies with the HRP-method show that the concept of a longitudinal pattern in the cerebellum is scarcely generally valid of the entire olivocerebellar projection. Within the projections of the lateral half of the dorsal accessory olive and the area in the rostral part of the medial accessory olive there appears to be a topical relation with the folial pattern in the anterior lobe. An analysis of the findings with reference to the afferents traced anatomically to the various olivary areas permits some conclusions as to the functional role of the olivary areas. Comparison with Oscarsson's ('73) diagram of the sites of termination of two of the spinal-olivary pathways (his DF-SOCP) and VF-SOCP) permits an anatomical explanation as concerns the projections to the vermis, while correlations as concerns the intermediate part are less satisfactory.

The olivocerebellar projection in the cat studied with the method of retrograde axonal transport of horseradish peroxidase. VI. The projection onto longitudinal zones of the paramedian lobule.

Microinjections (30-50 nl) of a horseradish peroxidase (HRP) suspension of 25% (wt./vol.) were made in different folia of the paramedian lobule of cats, and the sites of occurrence of labeled cells in the inferior olive were precisely determined. In each case only a small number of cells are labeled, aggregated in a minute area. The labeled cells are found within three only of the four olivary areas previously determined (Brodal et al., '75) to project onto the paramedian lobule (fig. 1): one area in the rostral half of the medial accessory olive, another in the dorsal accessory olive (except its caudalmost part), and a third in part of the caudal half of the dorsal lamella of the principal olive. Labeled cells were never found in the fourth area, the ventral lamella. A distinct zonal pattern in the projection is demonstrated (figs. 3, 5B): a middle longitudinal zone of the paramedian lobule receives olivary afferents from the area in the medial accessory olive, a medial zone from part of the projection area in the dorsal accessory olive, a lateral zone from part of the projection area in the dorsal lamella. This zonal projection appears to extend throughout the length of the paramedian lobule (the two caudalmost folia could not be studied). tthe somatotopical pattern in the projections from the accessory olives described previously (Brodal et al., '75) is confirmed. The pattern of a zonal projection obtained with the HRP-method (fig 5B) is simpler than that deduced by Armstrong et al ('74) from recordings of antidromic potentials in the olive (fig 5A). Concerning main points there is satisfactory agreement. The phenomenon that following microinjections of HRP in superficial parts of the folia labeled cells occur within parts only of the regions of the olive which contain labeled cells following large HRP-injections in the paramedian lobule is discussed.

The olivocerebellar projection in the cat studied with the method of retrograde axonal transport of horseradish peroxidase. VII. The projection to lobulus simplex, crus I and II.

The olivocerebellar projection to lobulus simplex, crus I and II in the cat was investigated by means of retrograde axonal transport of horseradish peroxidase (HRP). The distribution of labeled cells in the inferior olive following HRP injections in lobulus simplex, crus I and II confirmed the findings by Brodal ('40b) that the rostral half of the principal olive projects to these areas of the cerebellar hemisphere. However, concerning details there are some differences in so far as the heaviest contribution to crus I comes from the medial parts of the ventral and dorsal lamella, that to crus II from its lateral part, especially the ventral bend. The present findings show that in addition the rostral part of the medial and the rostromedial part of the dorsal accessory olive project to these areas of the cerebellar cortex. Further details in the projection are shown in figure 8B. The findings agree fairly well with the electrophysiological results of Armstrong et al. ('74) and the experimental anatomical data of Groenewegen and Voogd ('77a,b). An attempt is made to correlate the findings with the pattern of longitudinal zonal subdivision of the cerebellum. There is evidence for a topical organization within the projection to crus I and II and parts of their projection areas in the principal olive. The distribution of the labeled cells which project to lobulus simplex, crus I and II is discussed in relation to afferent pathways to the inferior olive.

The olivocerebellar projection in the cat studied with the method of retrograde axonal transport of horseradish peroxidase. III. The projection to the vermal visual area.

Horseradish peroxidase (HRP) was injected separately in one of the cerebellar lobules VI, VIIA, VIIB, VIIIA or VIIIB (together corresponding to the vermal visual area) in 17 cats. After 1-3 days the distribution of labeled cells in the inferior olive was mapped. In spite of some overlapping it is clear that the various lobules of the vermal visual area receive fibers from separate parts of a horseshoeshaped region in the caudal half of the contralateral medial accessory olive (fig. 5C). The projection area of lobule VIIA is found caudomedially and overlapping with the area supplying lobule VIIB. This in addition receives a few fibers from the nucleus beta. Fibers terminating in lobule VIIIA arise caudolaterally as do fibers destined for lobule VIIIB. A central part of the total projection area projects to lobule VI. Following injections leading to a similar extent of cortical staining in lobules VI, VII or VIII the projection of labeled cells in the corresponding projection areas differ markedly. In the area of lobule VII apparently all cells are labeled, in the area of lobule VI the density of labeled cells is considerably less, and in that of lobule VIII there are rather few labeled cells. In a few cases with widespread staining of the cerebellar visual area there was spreading of HRP to the nucleus fastigii. The projection to this form the olive was therefore investigated to avoid erroneous conclusions. In the discussion it is pointed out that on most points our findings agree fairly well with the results of studies of the olivocerebellar projection undertaken with other methods (studies of retrograde cellular changes, electrophysiological methods). No support for a longitudinal subdivision of lobules VI-VIII was found. Studies of the available literature indicate that the areas in the medial accessory olive projecting onto lobules VI-VIII probably do not receive direct afferents from regions which are known to be concerned in the transmission of visually evoked impulses. Fibers to the olive from the superior colliculus appear to pass to the nucleus beta only. This projects mainly to the uvula, to a little extent only to lobule VII. However, it may be imagined that visual impulses may reach the vermal visual area via the inferior olive by way of intercalated neurons, for example in the mesencephalic RF. Major contingents of afferents to the olivary regions projecting onto the vermal area come from the spinal cord, the motor cortex and the periaqueductal gray.

The olivocerebellar projection in the cat studied with the method of retrograde axonal transport of horseradish peroxidase.

The distribution of labeled cells in the inferior olive of the cat has been mapped following injections of small amounts of horseradish perosidase in the paramedian lobule of the cerebellum. The distribution of labeled cells was plotted in drawings of approximately serial transverse sections. The findings in each case were transferred to a standard diagram of the olive to facilitate comparison of cases. Previous studies of the distribution of retrograde cell loss in the inferior olive following cerebellar lesions (Brodal, '40b) showed that fibers ending in the paramedian lobule come from the caudal part of the ventral lamella of the principla olive. This was confirmed with the peroxidase method, but in addition three other separate and well circumscribed area of the olive showed labeling: one in the dorsal accessory olive, another in the rostral part of the medial accessory olive, a third in the caudal part of the dorsal lamella of the principal olive (fig. 7). There is some degree of topical arrangement within the projection of each of these olivary areas to the paramedian lobule. It is particularly striking that the projection areas of the caudal one-third of the lobule are different from and overlap only little with those of the orstral two-thirds. On account of diffusion of the injected perosidase solution in the folia it could not be decided whether the different olivary areas project to particular longitudinal zones in the paramedian lobule. The main findings can be correlated with the physiological observations of Armstrong et al. ('74). Some of the "paramedian" olivary areas are labeled also following peroxidase injections in other cerebellar parts, among them the nuclei interpositus anterior and posterior. The findings are compatible with the notion that olivocerebellar fibers branch to supply more than one cerebellar region. It is confirmed that the olivocerebellar projection, including that of the nuclei, is almost completely crossed. In the discussion it is emphasized that afferents from several sources converge on all four olivary regions projecting onto the paramedian lobule. The olivocerebellar projection obviously allows for divergence as well as convergence of impulses from the olive to the cerebellum. For further insight into the anatomical organization of the inferior olive, the entire olivocerebellar projection has to be mapped with the peroxidase methods, and further studies of the afferents to the olive are needed. In such studies, as well as in physiological ones, it is essential that findings are described with meticulous reference to the topography of the olivary subdivisions.

An electron microscopic, immunogold analysis of glutamate and glutamine in terminals of rat spinocerebellar fibers.

A semiquantitative, electron microscopic immunocytochemical procedure based on the use of colloidal gold particles as markers was employed to analyze the subcellular distribution of glutamate and glutamine, a major glutamate precursor, in a subpopulation of spinocerebellar mossy fiber terminals. These terminals were identified by anterograde transport of a horseradish peroxidase-wheat germ agglutinin conjugate, injected in the thoracic spinal cord. Gold particles signalling glutamate-like immunoreactivity were enriched over clusters of synaptic vesicles relative to organelle-free cytoplasmic matrix, and there was a strong positive correlation between gold particle and synaptic vesicle densities (correlation coefficient 0.94). Gold particles indicating glutamine-like immunoreactivity showed a much weaker correlation with vesicle density (correlation coefficient 0.36) and were about equally concentrated over cytoplasmic matrix as over clusters of synaptic vesicles. Compared with the mossy fibers, the putative GABAergic Golgi cell terminals exhibited a lower level of glutamate-like immunoreactivity, which was very weakly correlated with the vesicle density (correlation coefficient 0.27). The level of glutamine-like immunoreactivity in the Golgi cell terminals was similar to that in mossy fibers, but much lower than that in glial cells. The anterogradely labelled mossy fiber terminals were not enriched in immunoreactivities for aspartate or GABA. These results suggest that the level and subcellular distribution of glutamate in presumed glutamatergic terminals differs from that in terminals in which glutamate only serves metabolic or precursor roles, and that these differences can be exploited in immunocytochemical studies aimed at identifying glutamate-using neurons. In contrast, glutamine immunocytochemistry does not seem to be generally useful in this regard.

Ultrastructure of spinal efferents to the lateral reticular nucleus: an EM study using anterograde transport of WGA-HRP complex.

Anterograde transport of lectin-conjugated horseradish peroxidase and subsequent incubation with tetramethylbenzidine were employed to label the spinal terminals within the feline lateral reticular nucleus (NRL) for ultrastructural identification. Quantitative studies demonstrated that compared to the unlabelled terminals the spinal boutons were more than twice as large and contained fewer synaptic vesicles. Most of the synaptic contacts of the labelled terminals were located on dendritic shafts but contacts on dendritic spines as well as perikarya were also present. In four cases (all with cervical injections), the postsynaptic cells could be studied in the transversal sections of the medulla in the nuclear plane. The neurons were large and elongated with longest and shortest diameters of about 60 X 30 microns, belonging to the largest category of cells within the NRL. The observations were discussed and related to the findings made in other studies of the NRL.

Metabolic compartmentation of glutamate and glutamine: morphological evidence obtained by quantitative immunocytochemistry in rat cerebellum.

An electron microscopic, double-labelling immunocytochemical procedure was used to assess the level of fixed glutamate and glutamine in different cell profiles in ultrathin sections of rat cerebellar cortex. The procedure was based on sequential immunolabelling with two rabbit antisera, using gold particles of different sizes as markers and formaldehyde vapour as a means to avoid interference between the two incubations. Model sections containing a series of known concentrations of the respective amino acids (aldehyde--fixed to rat brain protein) were incubated together with the tissue material. These revealed a close to linear relationship between gold particle density and antigen concentration throughout the range of biological relevance. The ratio between the density of the two categories of gold particles was calculated for the individual profile types. This ratio showed a 20-fold variation, with the highest glutamate/glutamine ratios obtained for putative excitatory terminals (terminals of parallel fibres in the outer part of the molecular layer, followed by mossy and climbing fibre boutons) and the lowest for glial cells (Bergmann glia, astrocytes in the granule cell layer, and oligodendrocytes). Granule cell bodies and dendrites, and cell bodies and processes of putative GABAergic cells (Purkinje, basket and Golgi cells) displayed intermediate ratios. The ratios corresponded to millimolar ratios (mM fixed glutamate/mM fixed glutamine) ranging from 4.5 to 0.2, tentatively assessed by adjusting for differences in labelling efficiency of the two antigens. Our results show that the compartmentation of glutamate and glutamine, an issue previously addressed mainly in the test tube, can be studied in morphologically intact preparations at a resolution that matches the complexity of CNS tissue. The data indicate that glutamate is effectively converted to glutamine in all categories of glial cells, and that glutamate synthesis prevails in each of the three types of excitatory terminals in the cerebellar cortex. Terminals of putative GABAergic cells form a distinct low glutamate/low glutamine compartment.

Aspartate-like and glutamate-like immunoreactivities in the inferior olive and climbing fibre system: a light microscopic and semiquantitative electron microscopic study in rat and baboon (Papio anubis).

A post-embedding immunogold procedure was used to analyse, in a semiquantitative manner, the distributions of aspartate-like and glutamate-like immunoreactivities in the inferior olive and climbing fibre system in rats and baboons. The neurons in the inferior olive were uniformly labelled for aspartate as well as glutamate, indicating a 100% co-localization of these two amino acids in the cell bodies. The level of glutamate-like immunoreactivity in the climbing fibre terminals was similar to that in the parent cell bodies, as judged by a computer-assisted calculation of gold particle densities. In contrast, the level of aspartate-like immunoreactivity in the climbing fibre terminals was only one-seventh of that of the olivary neurons. No differences were found between the hemispheres and vermis. Nerve terminals in the inferior olive were generally moderately labelled with the aspartate antiserum, as were cell bodies of astrocytes. With a few exceptions, the results obtained in baboons were similar to those in rats. Notably, no evidence was found of an enrichment of aspartate-like immunoreactivity in climbing fibres. The present results do not support previous data suggesting that aspartate is the transmitter of the climbing fibres but indicate that glutamate or another excitatory compound should be considered as candidate for this role. Our findings show that the presence of aspartate-like immunoreactivity in cell bodies is an unreliable indicator of transmitter identity.

Do pontocerebellar mossy fibres give off collaterals to the cerebellar nuclei? An experimental study in the cat with implantation of crystalline HRP-WGA.

In 15 cats with implantations of crystalline HRP-WGA in the cerebellar nuclei and tetramethylbenzidine histochemistry, the pontine nuclei were carefully examined for presence of retrogradely labelled cells. Findings in the nucleus reticularis tegmenti pontis and the inferior olive, both known to project to the cerebellar nuclei, served as controls for effectiveness of uptake and transport. After implantations restricted to the lateral cerebellar nucleus in 5 cats altogether two labelled cells were found in the contralateral pontine nuclei in regions receiving afferents from the lateral nucleus. In contrast, many labelled cells occurred in the nucleus reticularis tegmenti pontis and the inferior olive. After implantations in 5 cats restricted to the posterior or anterior interposed nuclei, altogether only one labelled cell was found in the pontine nuclei, while many labelled cells occurred in the inferior olive. The nucleus reticularis tegmenti pontis contained a small number of retrogradely labelled cells after implantations in the anterior interposed nucleus, but none after implantations restricted to the posterior interposed nucleus. After implantations restricted to the medial (fastigial) nucleus, no retrogradely labelled cells were found in the pontine nuclei and nucleus reticularis tegmenti pontis (although many were present in the inferior olive). The present findings support earlier conclusions based on anterograde tracing methods that the cerebellar nuclei receive very few, if any, afferents from the pontine nuclei.

The cerebellar nucleo-olivary and olivo-cerebellar nuclear projections in the cat as studied with anterograde and retrograde transport in the same animal after implantation of crystalline WGA-HRP. I. The dentate nucleus.

The implantation technique described by Mori et al. has been modified for the implantation of crystalline wheat germ agglutinin-horseradish peroxidase (WGA-HRP) complex. This method permits a detailed analysis of the afferent and efferent connections of the cerebellar nuclei without the complication of uptake and transport of the tracer into passing fibres. We have used this method for studies of the olivo-dentate and dentato-olivary projections in the cat. After implantation of WGA-HRP into the dentate nucleus in all our cases, both anterogradely labelled terminal dentato-olivary fibres and retrogradely labelled olivo-dentate neurons were found in the contralateral inferior olive. It appears from our findings that both projections are topically organized. The dorsal part of dentate nucleus is bidirectionally connected with the rostral part of the principal olive, the ventrolateral part of the dentate is connected with the intermediate portion of the principal olive, while its ventromedial part is connected with the caudal portion of the principal olive. The olivo-dentate and dentato-olivary connections appear to be largely reciprocally organized. The advantages and drawbacks encountered with implantation of crystalline WGA-HRP are discussed, and our observations are considered in relation to previous studies on the olivo-cerebellar and cerebello-olivary connections.

On the morphology of the mesencephalic trigeminal cells. New data based on tracer studies.

Injections of free horseradish peroxidase in the masticatory muscles of the cat resulted in retrograde labeling of not only large and small so-called pseudounipolar cells but also of multipolar neurons within the ipsilateral mesencephalic trigeminal nucleus. The latter cell type was present only in the pontine part of the nucleus, and usually more faintly labeled than the other cells. Several of the so-called pseudounipolar cells showed cell processes similar to dendrites of other cells, a finding indicating that the afferent connections of these cells are much more complex than hitherto assumed. The observations are discussed also with reference to the problem whether the multipolar cells should be considered as displaced locus coeruleus neurons.

The cerebellar nucleo-olivary and olivocerebellar nuclear projections in the cat as studied with anterograde and retrograde transport in the same animal after implantation of crystalline WGA-HRP. III. The interposed nuclei.

The bidirectional connections between the inferior olive and the cerebellar nuclei were investigated by means of anterograde and retrograde transport after implantation of crystalline wheat germ agglutinin-horseradish peroxidase complex in the interposed nuclei. The projections from the interposed nuclei to the inferior olive show a detailed topical arrangement. The main projection from the anterior interposed nucleus reaches the rostral two thirds of the dorsal accessory olive, while the main projection from the posterior interposed nucleus reaches the rostral half of the medial accessory olive. The projections from the inferior olive to the interposed nuclei show a more widespread distribution and appear to be less precisely organized. Both interposed nuclei receive afferents from the medial and dorsal accessory olives, the dorsomedial cell column, nucleus beta and the dorsal cap. Our findings give evidence that the olivo-interposed and interposito-olivary projections are in part reciprocally organized. Our observations are discussed and related to previous investigations on the cerebello-olivary and olivocerebellar pathways. Some methodological comments are made. It appears from our results that anterograde transport in some of our cases has occurred only from a restricted part of the stained area at the implantation site.

The interconnection between the vestibular nuclei and the nodulus: a study of reciprocity.

The reciprocal connections between the nodulus and the vestibular and perihypoglossal nuclei in the cat have been studied by anterograde and retrograde transport after implants of crystalline wheatgerm agglutinin-horseradish peroxidase complex (WGA-HRP) restricted to one or two nodular folia. The findings supplement the previous study by Epema et al. (Neurosci. Lett., 1985, 57: 273-278), who injected WGA-HRP into the vestibular nuclei. In that study, details concerning the nodular origin and termination of the fibres within the reciprocal connections were given; in the present study, details are given concerning the origin and termination of the fibres within the vestibular and perihypoglossal nuclei. Our observations give evidence that the nodulovestibular fibres are distributed to a somewhat larger area than that projecting back to the nodulus. The distribution of the labelled cells and fibres is shown in Fig. 2. Of the 4 main nuclei, it is only the lateral vestibular nucleus which is devoid of a reciprocal connection with the nodulus, while only groups x and z of the minor cell groups are found to have such projections. Of the perihypoglossal nuclei, it is only the nucleus praepositus hypoglossi which appears to be interconnected with the nodulus.

Studies on the cerebellar projections from the main and external cuneate nuclei in the cat by means of retrograde axonal transport of horseradish peroxidase.

The cerebellar projections from the main and external cuneate nuclei in the cat have been studied by means of retrograde axonal transport of horseradish peroxidase. The main projection from the external cuneate nucleus (ECN) is to the intermediate and, possibly, the small lateral part of lobule V and to the paramedian lobule on the ipsilateral side. The projection from the ECN to the cerebellar regions mentioned is topographically organized. Cells in the caudal part of the ECN send their axons to the caudal parts of lobule V and to the rostral part of the paramedian lobule. Cells in the rostral part of the ECN project to the rostralmost part of lobule V and to the folia in the caudal part of the paramedian lobule. The experimental study also shows that cells in the main cuneate nucleus (MCN) send their axons to the cerebellum. These axons, like those from the ECN, terminate in the intermediate part of lobule V of the anterior lobe and in the paramedian lobule. However, the axons of the cells in the MCN terminate only in the superficial parts of the folia, whereas those from the ECN terminate in the depth of the folia in these two cerebellar areas. The present study also gives evidence that cells in the ventral part of the gracile nucleus send their axons to lobules I and II of the anterior lobe vermis. The observations referred to here are to our knowledge the first anatomical findings demonstrating a projection from the main cuneate and gracile nuclei onto the cerebellar cortex. The observations confirm previous physiological studies.

A re-evaluation of the question of ascending fibers in the pyramidal tract.

In 1952 we published a study in the cat with the Glees method, demonstrating the occurrence of degenerating fibers in the pyramidal tract rostral to transections of the tract in the spinal cord. These fibers were interpreted as spinocortical fibers, which have also been described in man. However, other authors have disputed the existence of such fibers. In an attempt to provide more information about this subject, multiple injections of horseradish peroxidase (free and lectin-labeled) were made in the sensorimotor cortex of 4 cats. No retrogradely labeled cells were found in the spinal cord in these cases. Our present and previously reported findings are discussed in the light of other studies of pathological changes in fiber tracts within the central nervous system. Although the present experiments were negative, the degenerating axons previously observed by us in silver sections from the pyramid, pons and internal capsule after lesions of the pyramidal tract in the spinal cord, can not be satisfactorily explained as evidence of retrograde, indirect Wallerian, degeneration of corticospinal fibers.

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

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

Is there a reciprocal connection between the red nucleus and the interposed cerebellar nuclei? Conclusions based on observations of anterograde and retrograde transport of peroxidase-labelled lectin in the same animal.

The rubrointerposital projection was studied in cats where wheat germ agglutinin-horseradish peroxidase (WGA-HRP) was implanted in various parts of the interposed nuclei. No retrogradely labelled rubral cells were observed following implantations in the posterior interposed nucleus, and only very few such cells were identified in the contralateral red nucleus after implantations restricted to the anterior interposed nucleus with no contamination of cerebellar white matter or cortex. However, when WGA-HRP was delivered by a pressure injection, which in addition to the anterior interposed nucleus included the adjacent white cerebellar matter along the needle track and the overlying cortex, many retrogradely labelled cells were present contralaterally in the magnocellular red nucleus, with some also found in its rostral parvicellular part. The same observation was made when injection of free HRP exceeded the boundaries of the anterior interposed nucleus. These observations indicate that there is a negligible projection from the red nucleus to the contralateral interposed cerebellar nuclei. What has been considered to be rubrointerposital cerebellar fibres probably is the projection to the cerebellar cortex (Exp. Brain Res., 50 (1983) 353-358). Anterogradely labelled fibres could be followed from the implantations in the posterior interposed nucleus to a medial crescent of the entire contralateral red nucleus. Caudal as well as rostral parts of the posterior interposed nucleus project into the same area of the red nucleus. Implantations restricted to the anterior interposed nucleus label a projection to the contralateral magnocellular red nucleus which is topographically organized. The caudal part of the anterior interposed nucleus projects to the dorsomedial portion of the magnocellular red nucleus, the rostral part to its ventrolateral portion. In addition, a mediolateral organization in the anterior interposed nucleus coincides with a caudorostral arrangement in the red nucleus. This topical arrangement corresponds to what has previously been observed in cat and monkey, but due to the small implantation sites used in the present study a more precise mapping of the projection has been obtained. Furthermore, our implantations of WGA-HRP into the red nucleus show especially well the latter topical arrangement in the projection. The observations mentioned above are discussed and related to previous studies of the rubrocerebellar and cerebellorubral projections.

On retro- and anterograde transport of horseradish peroxidase in the pontocerebellar fibers as studied with the Mesulam TMB technique.

In cats where injections of HRP have been made in the cerebellar cortex, pontocerebellar fibers are visualized throughout their length. Likewise, injections of HRP into the pontine nuclei visualize the pontocerebellar fibers and these anterogradely stained axons can in fortunate sections be followed into the granular layer. A visualization of retrogradely filled pontocerebellar fibers was unexpected and its another example of the sensitivity of the Mesulam8 technique.