G. H. Hoddevik

Cerebellar afferent projections from the perihypoglossal nuclei: An experimental study with the method of retrograde axonal transport of horseradish peroxidase

SummaryDetails of cerebellar afferent projections from the perihypoglossal nuclei were studied in the cat by means of retrograde axonal transport of horseradish peroxidase (HRP). Labeled cells were observed bilaterally (with a preponderance ipsilaterally) in nuclei intercalatus and praepositus hypoglossi following injections in various folia of the entire vermis, paraflocculus, flocculus, fastigial nucleus, and the nucleus interpositus anterior and posterior. Relatively high densities of labeled cells were found in nucleus intercalatus following injections in the anterior part of the vermis, whereas labeled cells in nucleus praepositus hypoglossi were found more frequently following injections in the posterior part of the vermis. Labeled cells in the nucleus of Roller were found only following injections in the anterior lobe vermis, posterior vermal lobules VI and VII, in the flocculus and in the nucleus interpositus anterior. No labeled cells could be detected in the three subdivisions of the perihypoglossal nuclei following HRP injections in crus I, crus II, paramedian lobule, and lateral cerebellar nucleus. The distribution of the HRP positive cells indicated the presence of a topographically organized projection from certain regions of the perihypoglossal nuclei to different parts of the cerebellum. The afferent and efferent connections of the perihypoglossal nuclei in relation to a functional role in eye and head movements are discussed.

The projection from nucleus reticularis tegmenti pontis onto the cerebellum in the cat

SummaryFollowing stereotactically performed lesions in nucleus reticularis tegmenti pontis (N.r.t.) degenerating fibers are traced to the contralateral N.r.t., to the pontine nuclei, through brachium pontis to restricted areas of the cerebellar nuclei and to most parts of the cerebellar cortex where they terminate in the granular layer. Most degenerating fragments are found in the contralateral half of the cerebellum with the greatest density in the vermal lobules VI and VIIA and in the flocculus.Following injections of HRP in the various cerebellar lobules labeled cells are mainly present within limited groups in the N.r.t.. Injections in vermal lobules VI-VIII B give rise to labeled cells within circumscribed areas in the dorsal and ventral parts throughout the rostrocaudal extent of the N.r.t.. In cases with injections in lobule IX or the ventral paraflocculus labeled cells are found ventrally in the rostral half of the N.r.t., while following injections in the vermal lobules I-V labeled cells are mainly found in the ventral and caudal part of the N.r.t.. Following injections in the intermediate and lateral parts of the anterior lobe, Crus I and II, the paramedian lobule and the dorsal paraflocculus labeled cells occur within groups in medial and lateral parts throughout the rostrocaudal extent of the N.r.t.. Following injections in the flocculus labeled cells are found in a very distinct group in the dorsal and rostral part of the N.r.t., While an injection in the nodulus (lobule X) gave rise to a smaller group of labeled neurons in the dorsolateral corner in the caudal part of the N.r.t.. Labeled cells within processus tegmentosus lateralis (p.t.l.) are only found following injections in lobules VI-VIIIA, Crus I and II and the dorsal paraflocculus.From what is known about afferents to the N.r.t., it is concluded that no cerebellar lobule gets information from one only of these sources via the N.r.t.. Visual information can probably be mediated from the superior colliculus via the N.r.t. to the flocculus and to a minor extent to the vermal lobules VI-VIII B, and from the pretectum via the N.r.t. to both vermal and lateral parts of the cerebellum.

A note on the method of retrograde transport of horseradish peroxidase as a tool in studies of afferent cerebellar connections, particularly those from the inferior olive; with comments on the orthograde transport in Purkinje cell axons

Summary1.Injections of horseradish peroxidase (HRP) suspension were made in the cerebellar cortex of cats (most often the paramedian lobule). The staining of the cerebellar cortex and the ensuing labeling of neurons in the inferior olive were studied in experiments with variations of concentration of HRP, amounts of fluid injected, survival time and age of the animals. Light microscopical studies were supplemented with electron microscopical observations. The folded cerebellar cortex offers particular difficulties with regard to obtaining a predictable extent of stained tissue, and the spreading of the fluid within the cortex shows great variations even with the same amounts and concentrations of HRP suspension. Diffusion of fluid appears to occur most easily within the molecular layer. Often there are unstained parts of folia between stained parts. Staining of the cortex is barely visible after 7 days, but appreciable shrinking of the stained area does not appear to occur until after 4 days.2.The first signs of labeling of olivary neurons are seen after 5–10 hours, after 7 days there are no labeled cells. The rate of retrograde transport in olivocerebellar fibers is calculated to be between 50 and 100 mm/day. Labeling of cells appears to require staining of the molecular layer of its projection areas in the cerebellum.3.For studies of the olivocerebellar projection survival times of 2–3 days and injections of 0.5 μl of a 50% HRP suspension seem in general to be well suited. Best results are obtained with animals weighing 1–3 kg. There is a clearcut correlation between the site of staining of the cortex of a particular part of the cerebellum and the site(s) and extension of olivary area(s) containing labeled cells.4.Anterograde transport in axons of Purkinje cells has been observed. Electron microscopically the axons of these fibers contain HRP labeled tubules and vesicles as do their terminal boutons in the nuclei.5.In cases where the injected fluid has spread to the cerebellar nuclei, localized parts contain neurons which are labeled as are the cells in the injected cerebellar cortex.

The pontocerebellar projection onto the paramedian lobule in the cat: An experimental study with the use of horseradish peroxidase as a tracer

Horseradish peroxidase (HRP) was injected into cerebellar cortex of the paramedian lobule in 12 cats, and the ensuing distribution of labeled cells in the pontine nuclei was mapped in some detail. The cells in the pontine gray which give origin to fibers to the paramedian lobule lie together, in part in groups, and in part in columns. The columns are situated both medial and ventrolateral to the peduncle, as well as in the dorsolateral pontine nucleus. The projection is bilateral with a clearcut contralateral preponderance, except in the lateralmost region in the dorsolateral nucleus, which projects mainly ipsilaterally. The column medial to the peduncle projects in a topographical pattern to the paramedian lobule. The dorsal part of this column projects to the rostral folia of the paramedian lobule, while successively more ventral parts in the column project to more caudal paramedian lobules. Within the other columns only a faint sign of a topographical organization is found. The location of the pontine columns projecting onto the paramedian lobule largely corresponds to the pontine terminal areas of fibers from the sensory cerebral cortex (SmI and SmII). The corresponding topography in these parts of the corticopontine and pontocerebellar pathways is suitable for a somatotopical impulse transmission from the sensory cortex to the paramedian lobule, in agreement with the results of physiological investigations. Furthermore, a correlation of the pontine areas projecting onto the paramedian lobule with the terminal areas of pontine afferents shows that the pons may be a relay station in mediating influences from other parts of the cortex (MsI, visual and acoustic), the cerebellar nuclei and the colliculi to the paramedian lobule.

The pontine projection to the flocculonodular lobe and the paraflocculus studied by means of retrograde axonal transport of horseradish peroxidase in the rabbit

SummaryThe occurrence and distribution of labeled cells in the pontine nuclei were mapped following injections of small amounts of horseradish peroxidase (0.05–0.5 μl, 50% suspension) in the flocculus, nodulus and the dorsal and ventral paraflocculus in adult albino rabbits. While no labeled cells were found in the pontine nuclei following injections in the nodulus, some were present following injections in the flocculus and a great number following injections in the paraflocculus. The projections onto the flocculus and paraflocculus are precisely organized. Following injections in the paraflocculus labeled neurons are arranged in four columns (E and G in the paramedian pontine nucleus, F in the peduncular and H in the dorsolateral nucleus). Following injections in the ventral paraflocculus labeled cells are present only in parts of column E and F, while columns G and H and parts of E and F project onto the dorsal paraflocculus. Following injections in the flocculus labeled cells occur in the rostral part of column E only.A comparison between the sites of termination of pontine afferents and the areas giving origin to floccular and parafloccular fibers shows that only few fibers mediating visual impulses end in these pontine areas, while they receive numerous fibers from gyrus cinguli and areas 18 and 19 of the cerebral cortex.

The reticulovestibular projection in the cat. An experimental study with silver impregnation methods

The distribution of degeneration in the vestibular nuclei (VN) has been studied in transversely cut sections from 9 cats with stereotaxically performed lesions in the main reticular formation (RF) of the brain stem (Nauta of Fink and Heimer method). No projection was found from the mesencephalic reticular formation (R.mes.) and nucleus reticularis ventralis (R.v.). However, the reticular nuclei gigantocellularis (R.gc.), parvocellularis (R.p.c.) and pontis oralis (R.p.o.) were found to project bilaterally onto the 4 main vestibular nuclei with an ipsilateral overweight. By far the greates contribution comes from the R.gc. and R.p.c. In cases with R.gc. lesions some degeneration was found in the small cell groups x and f. The latter is also supplied from the R.p.c. The distribution of degeneration within the vestibular complex is rather diffuse, but a certain pattern can be discovered. After R.p.c. lesions the maximal terminal field in the VN is found within the superior nucleus, while the lateral and medial nuclei are preferred sites of termination of fibers from R.gc. and R.p.c. The projections of the R.gc. and the R.p.c. may be more different than appears from our findings since lesions of one of them will most likely have affected some ascending or descending fibers emanating from the other. Since the areas of RF projecting to VN receive afferents from many sources, these sources have possibilities to act on the VN even if they do not possess direct connections with this nuclear complex. These possibilities should be remembered in physiological studies of responses in the VN following stimulation of many parts of the CNS.

The olivocerebellar projections to the flocculus and paraflocculus in the cat, compared to those in the rabbit. A study using horseradish peroxidase as a tracer.

The projections from the inferior olive to the flocculus and paraflocculus in the cat have been mapped by means of the method of retrograde axonal transport of horseradish peroxidase. The findings show that the afferents to the flocculus are derived from the dorsal cap, ventrolateral outgrowth, the principal olive (the caudal parts of the ventral and dorsal lamella) and from the rostral part of the medial accessory olive. The fibres to the paraflocculus come from the caudal part of the principal and from the rostral part of the medial accessory olive. Details in the projections are seen from Figs. 1 and 2. Concerning some points the findings are at variance with those made in the rabbit by Hoddevik and Brodal, and suggest that there are species differences hitherto not known.

The pontocerebellar projection to the uvula in the cat

SummaryThe occurrence of retrogradely labeled cells in the pontine nuclei was mapped following injections of 0.3–0.4 μl of a horseradish peroxidase suspension (50% weight/volume) into the uvula (lob. IX of Larsell) in the cat. The uvula was found to receive afferents from three pontine cell collections. One of these is situated in the paramedian pontine nucleus close to the midline. It forms a fairly distinctly outlined longitudinal column of cells and is present at all levels of the pons except most rostrally and caudally. Another group, in the dorsolateral and lateral pontine nuclei, extends as a somewhat shorter cell column in the longitudinal direction. The third region consists of cells within the rostral part of the peduncular nucleus in its dorsomedial region. The pontine projection to the uvula is bilateral, with some preponderance of crossed connections.The projection to the uvula is organized according to the pattern determined previously for pontine projections to other parts of the cerebellum. A single lobule or part of it receives afferents from more than one cell group in the pons. The projecting cells are most often arranged in longitudinal columns.Correlations with data on the termination of afferents to the pons permit some conclusions regarding the sources of information reaching the uvula via the pons. Main sources seem to be the superior and inferior colliculi, the intracerebellar nuclei and the sensorimotor cortices.

The pontine projection onto longitudinal zones of the paramedian lobule in the cat

SummaryThe distribution of labeled cells in the pontine nuclei was studied following microinjections of horseradish peroxidase into three longitudinal zones in the paramedian lobule in the cat. Labeled cells were only found when the staining of the cerebellar cortex included the granular layer. The labeled cells were present contralateral to the injection site in the cases with the smallest injections, in the others there was a bilateral distribution with a contralateral preponderance. The labeled cells lie concentrated in three groups medially, ventrally, and laterally to the peduncle. No indication of a different projection from these three groups to the three longitudinal paramedian zones was found, although in the same material a zonal projection exists for the climbing fibers from various parts of the inferior olive to the same cerebellar lobule (Brodal and Walberg, 1977).

The reticulocerebellar projection in the cat as studied with retrograde transport of horseradish peroxidase

SummaryInjections of horseradish peroxidase into the various parts of the cerebellar cortex and the cerebellar nuclei in the cat result in labelled cells within the reticular formation proper. All the reticular nuclei (with the exception of the reticular formation of the mesencephalon) send fibres to the cerebellum. The highest number of labelled neurons after cerebellar injections is found in the caudal reticular formation, especially within nucleus reticularis ventralis, nucleus reticularis lateralis and nucleus reticularis gigantocellularis. Another region for an accumulation of labelled cells is the rostral part of nucleus reticularis pontis caudalis.Except for the paraflocculus, all cerebellar cortical areas and all cerebellar nuclei receive afferents from one or more of the nuclei within the reticular formation proper, but the largest number of labelled neurons is observed in cases with injections including the intermediate-lateral part of lobulus simplex and the adjacent areas of the anterior lobe and crus I. The projection is bilateral with an ipsilateral preponderance (the cerebellar nuclei appear to receive a higher number of fibres from the contralateral side). Cells of all sizes are labelled, but labelled giant cells are found only after large cortical injections.