Olivocerebellar connections in sheep studied with the retrograde transport of horseradish peroxidase

We describe here the morphology of the inferior olive and the localization of labeled cells after HRP injections into various lobules of vermis and hemisphere of the cerebellum of the sheep. The medial part of the caudal half of the medial accessory olive projects to a medial zone in the anterior lobe, the simple lobule, and the lobules VII and VIII. The lateral part of the medial accessory olive projects to more lateral parts of these lobules with the exception of lobule VII. The group beta projects in a differential manner to the lateral parts of the lobules VII and VIII and the medial parts of the lobules IX and X. The dorsomedial cell column projects to lobules VIII, IX, and X; the connections of the dorsal cap are restricted to lobule X. Fibers from the caudal limb of the dorsal accessory olive terminate in the B zone, the simple lobule, and in lobule VIII. The rostral half of the medial accessory olive projects to lobule IX and to the hemisphere. The other projections of the accessory olives and the principal olive to the hemisphere are similar to those reported for the cat. An accessory cell group in the sheep, located between the principal and the dorsal accessory olive, has connections with the caudal vermis and the hemisphere.     

Olivary projections from the mesodiencephalic structures in the cat studied by means of axonal transport of horseradish peroxidase and tritiated amino acids

By means of horseradish peroxidase (HRP) and autoradiographic methods, olivary projections from mesodiencephalic structures were studied in the cat. Following HRP injections in various parts of the inferior olive, many cells were labeled ipsilaterally in the nucleus of Darkschewitsch, the nucleus accessorius medialis of Bechterew, the nucleus of the fields of Forel, and the subnucleus dorsomedialis and ventrolateralis of the parvocellular red nucleus. Some labeled cells also occurred ipsilaterally in the suprarubral reticular formation and a few labeled cells in the interstitial nucleus of Cajal. After injection of tritiated amino acids in different parts of the mesodiencephalic region mentioned above, labeled fibers were found in different parts of the inferior olive, presenting a high degree of the topographic correlation within the mesodiencephalo-olivary projection, which was exclusively ipsilateral. That is, the nucleus of Darkschewitsch was found to project to the rostral half of the medial accessory olive and the dorsomedial cell column. There was mediolateral topographic relation in this projection. The nucleus accessorius medialis of Bechterew was found to project to the ventral lamella and the lateral part of the dorsal lamella as well as to a small rostromedial part of the caudal half of the medial accessory olive. The subnucleus dorsomedialis and ventrolateralis of the parvocellular red nucleus projected to the rostral and caudal halves, respectively, of the medial part of the dorsal lamella. The subnucleus ventrolateralis of the parvocellular red nucleus also sent fibers to the lateral part of the ventrolateral outgrowth. The nucleus of the fields of Forel, suprarubral reticular formation, and interstitial nucleus of Cajal appeared to project to the caudal half of the medial accessory olive, the medial part of the ventrolateral outgrowth, the rostral part of the dorsal cap, and the caudal part of the dorsal accessory olive.     

Cholinergic projection to the dorsal cap of the inferior olive of the rat,rabbit, and monkey

The inferior olive is divided into several subnuclei that receive specific sensory information. The caudal dorsal cap of the medial accessory subdivision of the inferior olive receives horizontal optokinetic information from the nucleus of the optic tract. The immediately subjacent b?-nucleus receives vertical vestibular information mediated by a GABAergic pathway originating from the ipsilateral descending and medial vestibular nuclei. None of the transmitters to the dorsal cap have been identified. Using choline acetyltransferase (ChAT) immunohistochemistry, we have identified a cholinergic pathway that terminates exclusively in the dorsal cap of rats and monkeys. No other division of the inferior olive received a significant cholinergic innervation. In the rabbit, immunostaining for ChAT reveals a weaker and more diffuse cholinergic innervation of both the dorsal cap and the subjacent b?-nucleus. In rats and rabbits we injected iontophoretically the orthograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) into the medial and descending vestibular nuclei (MVN, DVN) as well as the nucleus prepositus hypoglossi (NPH) in order to trace the possible origin of the cholinergic projection. PHA-L injections into the NPH and medial aspect of the MVN labeled terminals within the contralateral dorsal cap. PHA-L injections in the central and lateral aspects of the MVN as well as the DVN labeled the ipsilateral b?-nucleus. Pressure injections of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) in the caudal dorsal cap of the rabbit inferior olive demonstrated a predominantly contralateral projection to the dorsal cap from the lateral aspect of the NPH. However, pressure injections of HRP into the caudal dorsal cap combined with ChAT immunohistochemistry in the rabbit demonstrated that most of the neurons of the NPH that projected to the dorsal cap were not cholinergic, and that most of the ChAT-positive neurons within the NPH occupied a more ventral location than the neurons within the NPH that were retrogradely labeled from the HRP injection into the contralateral dorsal cap. In the rat, we made lesions in the MVN, DVN and NPH by injection of ibotenic acid (0.3–0.5 m?l), in an attempt to deplete the dorsal cap of the inferior olive of its cholinergic input. Lesions confined to the NPH and medial aspect of the MVN of the rat caused a loss of ChAT staining in the contralateral dorsal cap. Lesions placed more laterally within the MVN or DVN failed to deplete ChAT-positive terminals in the contralateral or ipsilateral dorsal caps. The dorsal cap of the rat and monkey receives a discrete cholinergic projection. In the rat, this projection originates from the contralateral NPH. In the rabbit, the caudal inferior olive receives a weak cholinergic projection. The dorsal cap receives a projection from the contralateral NPH. However, this projection is mediated by a non-cholinergic transmitter. © 1993 Wiley-Liss, Inc.     

GABAergic neurons in the mammalian inferior olive and ventral medulla detected by glutamate decarboxylase immunocytochemistry.

Neurons containing glutamic acid decarboxylase (GAD) (presumed GABAergic neurons) were mapped by immunocytochemistry in the ventral medulla of rat, rabbit, cat, rhesus monkey, and human, with emphasis on the inferior olive. In all species, three categories of GABAergic neurons were identified: periolivary neurons in the gray matter and the white matter surrounding the inferior olive, internuclear neurons located in the white matter between the subnuclei of the inferior olive, and intranuclear neurons located within the olivary gray matter. The intranuclear GABAergic neurons of the inferior olive had a characteristic morphology which differed from non-GABAergic olivary neurons; they were usually smaller, and, wherever their processes were stained, they had radiating, sparsely branching dendrites. They were also usually distinguished from the other GABAergic neurons by their smaller size. The intraolivary GABAergic neurons constituted only a minor proportion of the total olivary neuronal population, but they were concentrated in regions of the olive that varied by species. In the rat, they were situated in the rostral tip of the medial accessory olive and in the caudal subdivision of the dorsal accessory olive, while in the rabbit, they were located in the caudal two-thirds of the medial accessory olive, in the dorsal cap, and in the ventral lateral outgrowth. Such neurons were extremely rare in the cat; only a few were found in the rostral parts of the principal olive, the medial accessory olive, and the dorsal accessory olive. In the rhesus monkey, the principal olive and the lateral region of the rostral medial accessory olive contained most of the intranuclear GABAergic neurons, but some were also present in the dorsal accessory olive. In the human, such neurons occurred in the principal olive, the dorsal accessory olive and the rostral medial accessory olive, but as in the rhesus monkey, most were observed in the principal olive.     

Development of the olivocerebellar projection in the rat: II. Matching of the developmental compartmentations of the cerebellum and inferior olive through the projection map.

A transient biochemical parcellation has been observed by immunocytochemical methods, during the perinatal development of both the inferior olive and the cerebellum. In the present study, we sought a relationship between this developmental compartmentation and the organization of the olivocerebellar projection. In the inferior olive, a transient parvalbumin immunoreactivity restricted to the dorsal cap of the medial accessory olive is observed around birth. The climbing fiber projection of the dorsal cap was identified in the cerebellum of newborn rats based on its parvalbumin immunoreactivity. The pattern of this projection, restricted to lobules IX and X of the vermis, and to the flocculus, is indistinguishable from that of the adult medial accessory olive, which was previously described from axonal tracing experiments. The parvalbumin immunoreactive climbing fibers were followed between birth and postnatal day 7. In the caudal vermis, Purkinje cell subpopulations can be identified between embryonic day 20 and postnatal day three, on the basis of their differential immunostaining with an antibody directed against a specific peptide, PEP 19. In lobule X, the parvalbumin immunoreactive climbing fibers form two sagittal bands on each side of the midline, one medial and one lateral. The medial parvalbumin immunoreactive climbing fiber band is coextensive with a PEP 19 negative Purkinje cell cluster, indicating a clear relationship between the biochemical parcellations of the cerebellum and inferior olive.     

Ultrastructural organization of the retino-pretecto-olivary pathway in the rabbit: a combined WGA-HRP tracing and GABA immunocytochemical study.

The ultrastructural organization of the pretecto-olivary projection neurons within the nucleus of the optic tract and dorsal terminal accessory optic nucleus of rabbits was studied by using anti-GABA immunolabelling and retrograde transport of WGA-HRP. GABA-like immunoreactivity was determined with a postembedding colloidal gold technique. WGA-HRP was injected in the dorsal cap of the inferior olive. The WGA-HRP-labelled neurons were incubated with gold-substituted silver peroxidase. Neurons projecting to the inferior olive had large to medium-sized cell bodies and were GABA negative. In the nucleus of the optic tract, projection neurons are found in the rostral parts, while the majority of the local GABAergic interneurons are mainly found in the caudal parts. In the dorsal terminal nucleus both types of neurons are intermingled. The projection neurons were frequently in synaptic contact by GABAergic terminals. These neurons also receive retinal afferents indicating the existence of a two-step synaptic connection from the retina to the inferior olive. It is suggested that this class of projection neurons forms the "direction-selective" neurons that can be antidromically stimulated from the inferior olive. The GABAergic terminals on the identified projection neurons are of axonal origin (F-terminals), whereas presynaptic dendrites of interneurons (P-terminals) were seldom observed to be in synaptic contact with retrogradely labelled profiles. The strong input of GABA on direction-selective neurons indicates that GABA is directly involved in modulating retinal signals to the inferior olive.     

Corticotropin-releasing factor mRNA increases in the inferior olivary complex during harmaline-induced tremor

This study reports that corticotropin-releasing factor (CRF) expression within the inferior olivary complex (IOC) of the cat is increased 8 h after administration of the tremor-inducing β-carboline harmaline. Following harmaline treatment, hybridization of an oligodeoxynucleotide complementary to CRF mRNA increased significantly in the dorsal accessory olive, subnuclei A and C of the medial accessory olive and the dorsal cap of Kooy, a subnucleus thought previously to be unresponsive physiologically to harmaline. At this early time point, greater increases in CRF mRNA hybridization were present in the caudal than the rostral IOC. These results support published reports that harmaline-mediated effects are more profound within the caudal than the rostral IOC, but also suggest that harmaline mediates cellular responses in inferior olivary neurons which are not related to activation of rhythmic firing.     

Afferent projections from the brainstem to the three floccular zones in cats. I. Climbing fiber projections

The cat's flocculus can be divided into 3 zones on the basis of differences in their efferent projection sites. In the present study, climbing fiber projections from the inferior olive to each zone of the flocculus were studied by means of retrograde axonal transport of horseradish peroxidase (HRP). Following large injections of HRP into the flocculus, labeled cells appear in the dorsal cap and the ventrolateral outgrowth of the principal olive. No HRP-labeled somata are present in other parts of the inferior olive. Following microinjections of HRP into the rostral of caudal zones of the flocculus, labeled cells appear in the ventrolateral outgrowth and the rostral part of the dorsal cap, while, after injections into the middle zone, labeled cells are found in the caudal part of the dorsal cap. These findings show that there exists zonal organization in the climbing fiber projections to the flocculus; the rostral and caudal zones receive climbing fiber afferents from the ventrolateral outgrowth and the rostral part of the dorsal cap, while the middle zone receives those from the caudal part of the dorsal cap.     

The inferior olivary connections to the cerebellum in the rat studied by retrograde axonal transport of horseradish peroxidase

Olivocerebellar projections were investigated in the rat using retrograde axonal transport of horseradish peroxidase. Discrete cell groups of the inferior olive were labelled, subsequent to injections in the paravermal region, the vermis, or the caudolateral hemisphere. Injections in the midrostrocaudal third of the paravermal area resulted in labelling of cells in the medial accessory olive (MAO), in cell group “b” at caudal levels, and in its lateral portion at mid-rostrocaudal levels. The rostral pole of the principal olive (PO), the dorsal accessory olive (DAO), and the dorsomedial cell column, were heavily labelled. By comparison, caudal paravermal injections resulted in labelling in the medial part of the mid-rostrocaudal levels of the MAO, but not in its caudal portion. The PO lamellae were labelled in their lateral half, excluding the lateral bend connecting them. Injections slightly lateral within this paravermal area gave no caudal MAO labelling, but did label cells in segments of both PO lamellae, medial to those in the previous case. From vermal injections, cell groups “b” and “c” of the caudal MAO were labelled, but no labelled cells were present in the PO. Subsequent to injections in the paramedian lobule, cells in the dorsal lamella of the PO were labelled. No cells of the MAO were labelled. These results are discussed in terms of specific labelling patterns and the general concepts of organization presently held for the Olivocerebellar system.     

Projections of the dorsal and lateral terminal accessory optic nuclei and of the interstitial nucleus of the superior fasciculus (posterior fibers) in the rabbit and rat

The projections of the dorsal and lateral terminal accessory optic nuclei (DTN and LTN) and of the dorsal and ventral components of the interstitial nucleus of the superior fasciculus (posterior fibers; inSFp have been studied in the rabbit and rat by the method of retrograde axonal transport following injections of horseradish peroxidase into oculomotor-related brainstem nuclei. The projections of the ventral division of the inSFp have been further investigated in rabbits with the anterograde axonal transport of 3H-leucine. The data show that the projections of the DTN, LTN, and inSFp are remarkably similar in rabbit and rat. The DTN projects heavily to the ipsilateral medial terminal accessory optic nucleus (MTN), nucleus of the optic tract, and dorsal cap of the inferior olive. The DTN projects sparsely to the ipsilateral visual tegmental relay zone and to the contralateral superior and lateral vestibular nuclei. The LTN and dorsal component of the inSFp are found to share the same basic connections; both project heavily to the ipsilateral nucleus of the optic tract and visual tegmental relay zone and send a moderately sized projection to the ipsilateral MTN. However, while the dorsal component of the inSFp sends significant ipsilateral projections to both rostral and caudal portions of the dorsal cap, only a few LTN neurons appear to follow this example and only by projecting to the rostral part of the dorsal cap. In addition, both the LTN and dorsal component of the inSFp send sparse contralateral projections to the MTN, nucleus of the optic tract, and visual tegmental relay zone; and the dorsal component of the inSFp also provides a sparse contralateral projection to both rostral and caudal portions of the dorsal cap. The ventral component of the inSFp projects heavily to the ipsilateral visual tegmental relay zone and moderately to the ipsilateral MTN and nucleus of the optic tract. The ventral inSFp projects sparsely to the contralateral MTN, the nucleus of the optic tract, and the visual tegmental relay zone. A few of its neurons target the ipsilateral dorsal cap of the inferior olive. Unlike the DTN (present study) and the MTN (Giolli et al.: J. Comp. Neurol. 227:228-251, '84; J. Comp. Neurol. 232:99-116, '85a), the LTN and the inSFp of the rabbit and rat lack projections to the superior and lateral vestibular nuclei.(ABSTRACT TRUNCATED AT 400 WORDS)     

A correlation between receptive field properties and morphological structures in the pretectum of the cat

Retinal terminals in the pretectum were labelled by anterograde axonal transport of horseradish peroxidase (HRP) after injecting the enzyme into one eye. Pretectal neurons were retrogradely labelled by HRP-injections into the dorsal cap of the inferior olive. Electrophysiological recordings were performed in the same animal. This procedure showed that direction-selective neurons in the nucleus of the optic tract (NOT) projecting to the dorsal cap of the inferior olive lie dorsal and lateral to the retinal terminal clusters. Direction-unselective neurons sensitive to high stimulus velocities (jerk-neurons) were localized within the areas of retinal terminal clusters. Both jerk-neurons and retinal terminal clusters never overlapped with retrogradely labelled neurons. Latency measurements to stimulation of the optic chiasm (OX) confirmed a monosynaptic W-cell projection to the direction-selective NOT cells and indicated a predominantly monosynaptic Y-cell projection to the jerk-neurons.     

Projections from the inferior olive to the cerebellar nuclei in the cat demonstrated by retrograde transport of horseradish peroxidase

The method of intracerebral injections of horseradish peroxidase has been applied to demonstrate a projection from the inferior olivary nucleus to the intracerebellar nuclei in the cat. Cells labeled by the transported enzyme can be observed in different regions of the olive according to the localization of the injection. The caudal half of the medial and dorsal accessory subdivisions, the dorsal cap and nucleus β project to the fastigial nucleus. In the rostral half of the olive, the accessory subdivisions of that nucleus and the dorsomedial cell column send fibers to the interposed nuclei while the principal olive and the ventrolateral outgrowth are connected with the dentate nucleus. It is likely that these fibers are collaterals of the climbing fibers.     

Organization of inferior olivary projections to the flocculus and ventral paraflocculus of the rat cerebellum.

The climbing fiber projection to the rat flocculus and adjacent ventral paraflocculus was investigated by using Phaseolus vulgaris-leucoagglutinin as an anterograde and horseradish peroxidase as a retrograde tracer. Large injections of horseradish peroxidase in the flocculus and ventral paraflocculus indicated that the climbing fibers to this region are derived exclusively from any of the following contralateral olivary regions: the dorsal cap of Kooy, the ventrolateral outgrowth, the caudal half of the ventral leaf of the principal olive near its lateral bend, and the rostral pole of the medial accessory olive. Subsequent anterograde and retrograde studies with small injections demonstrated that the latter area projects to the C2 zone, which runs caudally in the ventral paraflocculus and enters the caudal most aspect of the flocculus. The ventral leaf of the principal olive is connected to a D zone in the cerebellar hemisphere and paraflocculus, which, upon entering the ventral paraflocculus, divides into a caudal and rostral strip, termed FD and FD', respectively. The dorsal cap and the ventrolateral outgrowth each project to two distinct zones in the flocculus and part of the ventral paraflocculus. Two floccular zones, which are continuous with the parafloccular FD and FD' zones, receive their climbing fibers from the ventrolateral outgrowth. Two other zones, (FE and FE') receive their climbing fibers from the dorsal cap. The FE' zone is found at the rostral pole of the flocculus and is followed caudalwards by the FD', FE, FD, and C2 zones, respectively. The rostromedial part of the dorsal cap is connected to the continuation of the FE zone into the ventral paraflocculus. The observation that the dorsal cap and the ventrolateral outgrowth are both connected to a set of two alternating zones of floccular/ventral parafloccular Purkinje cells is in agreement with recent studies in the rabbit, and suggests that these zones reflect functionally distinct and discrete units related to specific aspects of visuomotor control.     

Functional compartmentalization in the flocculus and the ventral dentate and dorsal group y nuclei: an analysis of single olivocerebellar axonal morphology

The cerebellar cortex consists of multiple longitudinal bands defined by their olivocerebellar projection. Single olivocerebellar axons project to a narrow longitudinal band in the cerebellar cortex and to the cerebellar nucleus with their axon collaterals. This olivocortical and olivonuclear organization is related to the functional compartmentalization of the cerebellar system. To reveal the detailed morphologic organization in the flocculus and the cerebellar and vestibular nuclei, we examined olivocerebellar projection by reconstructing the entire trajectories of 19 single olivofloccular axons and by anterograde mapping with biotinylated dextran in the rat. The flocculus was composed of 12 longitudinal band-shaped compartments that subdivided 5 previously described zones. These longitudinal bands were innervated differentially by the caudal and rostral portions of the dorsal cap (DC) and the ventrolateral outgrowth (VLO) and the rostral pole of the medial accessory olive. Single olivofloccular axons with an average of 5.1 climbing fibers usually projected to a single longitudinal band in the flocculus and to the ventral dentate or dorsal group y nucleus with their collaterals. DC neurons projected moderately to the rostrolateral portion of the ventral dentate nucleus, whereas VLO neurons projected densely to the medial portion of the ventral dentate nucleus and the dorsal group y nucleus with rostrocaudal topography. DC and VLO neurons did not project to the vestibular nuclei, although floccular Purkinje cells projected to the vestibular, ventral dentate, and dorsal group y nuclei. The fine morphologically identified longitudinal bands and topographic olivonuclear projections were correlated with previous electrophysiologically defined functional zones in the flocculus and inferior olive.     

Substance P and serotonin immunoreactivity in the rat inferior olive

The present study analyzes in detail the distribution of substance P and serotonin immunoreactivity in the inferior olivary complex of the rat using the indirect antibody peroxidase-antiperoxidase technique. The entire dorsal accessory olive contains an abundance of substance P fibers and varicosities. In addition, the dorsal cap of Kooy, nucleus Beta, parts b and c of the medial accessory olive, and the dorsomedial cell column contain numerous substance P immunoreactive elements. Fibers and varicosities positive for serotonin are present throughout the entire dorsal accessory olive. In addition, the rostral medial accessory olive contains an abundance of serotonin immunostaining. Scattered serotonin immunoreactive elements are present in the principal olive in particular in the area immediately subjacent to the lateral aspect of the dorsal accessory olive. Only scant serotonin immunolabeling is present in the dorsal cap of Kooy, nucleus Beta and the dorsomedial cell column. Speculations on possible functional roles of these two putative neurotransmitters are presented.     

The anatomical organization of the cerebello-olivary projection in the cat.

The cerebello-olivary pathway in the cat has been examined using orthograde and retrograde neuroanatomical tracing techniques. The orthograde transport of 3H-leucine from injection sites in the deep cerebellar nuclei labeled dentate and interpositus projections to the rostral two-thirds of the contralateral inferior olivary complex. These projections are topographically organized, with the dentate nucleus projecting to the principal olivary nucleus and the posterior and anterior interpositus nuclei projecting to the medial and dorsal accessory olives respectively. Fibers from the ventral half of the dentate nucleus terminate in the lateral bend and ventral lamina of the principal olive, whereas the medial and lateral parts of the dorsal half of the nucleus project to the medial and lateral regions of the dorsal lamina respectively. It is apparent that the more caudal parts of the interpositus nuclei project to areas of the medial and dorsal accessory olives near the caudal end of the principal olivary nucleus, whereas neurons in the more rostral parts of the interpositus nuclei project to the more rostral areas of the accessory olivary nuclei. A connection between the fastigial ncleus and the inferior olive could not be demonstrated. The retrograde transport of horseradish peroxidase (HRP) from injections sites in the inferior olive labeled cells throughout the contralateral dentate and interpositus nuclei. The labeled cells were especially numerous in the ventral parts of the dentate and posterior interpositus nlclei. These HRP-positive neurons were consistently small (10--15 mu) ovoid or spindle-shaped cells, with relatively large nuclei and light-staining Nissl substance. This evidence strongly suggests that the cerebello-olivary pathway originates from a population of small neurons in the dentate and interpositus nuclei and projects to specific, topographically defined areas in the contralateral inferior olive.     

Somatosensory Trigeminal Projections to the Inferior Olive,Cerebellum and other Precerebellar Nuclei in Rabbits

We have analysed the pathways through which somatosensory information from the face reaches the inferior olive and the cerebellum in rabbits. We used wheatgerm agglutinin - horseradish peroxidase (WGA-HRP) to trace projections from all parts of the somatosensory trigeminal system to the olive, cerebellar cortex, the cerebellar deep nuclei and the pontine nuclei. Projections to the cerebellar cortex and inferior olive were verified using retrograde transport of WGA-HRP. Two regions of the inferior olive–the medial dorsal accessory olive and the ventral leaf of the principal olive–receive inputs from pars interpolaris (Vi) and rostral pars caudalis (Vc) of the spinal trigeminal nucleus and from the principal trigeminal nucleus (Vp). Another area in the caudal medial accessory olive receives inputs from rostral Vo (pars oralis of the spinal trigeminal nucleus), caudal Vi and Vc. There are trigemino-olivo-cortical inputs to lobule HVI via all these olivary areas and to the paramedian lobe via the principal olive only. Cerebellar cortex–lobules HVI, crus I and II, paramedian lobe and IX–receives direct mossy fibre inputs from Vp, Vo and rostral Vi. The pontine nuclei receive an input only from rostral Vi. We saw no trigeminal projections to other precerebellar nuclei or to the deep cerebellar nuclei. The concentration of face somatosensory cortical inputs, via several pathways, upon lobule HVI may underlie its important role in the regulation of learned and unlearned eyeblinks.