Zonal organization of olivocerebellar projections to the uvula in rabbits

Plane-specific Purkinje cell responses to vertical head rotations in the cat cerebellar nodulus and uvula

We recorded simple spike (SS) and complex spike (CS) firing of Purkinje cell in the cerebellar nodulus and uvula of awake, head-restrained cats during sinusoidal vertical rotation of the head in four stimulus planes (pitch, roll, and two vertical canal planes). Two SS response types (position- and velocity-types) with response phases close to those of head position and velocity, respectively, were recognized. Optimal response planes and directions for SS and CS of each cell were estimated from the response amplitudes in the four stimulus planes by fitting with a sinusoidal function. The principal findings are as follows: 1) two rostrocaudally oriented functional zones of Purkinje cells can be distinguished; 2) the medially located parasagittal band is active during rotation in the pitch plane; 3) the laterally located band is active during rotation in the roll plane. These two zones are the same as previously reported zones in the cerebellar flocculus active during head rotation in the canal planes in the point that both cerebellar sagittal zones are plane-specific functional zones, suggesting that the anatomical sagittal zones serve as functional plane-specific zones at least in the vestibulocerebellum.

Visuomotor cerebellum in human and nonhuman primates

In this paper, we will review the anatomical components of the visuomotor cerebellum in human and, where possible, in non-human primates and discuss their function in relation to those of extracerebellar visuomotor regions with which they are connected. The floccular lobe, the dorsal paraflocculus, the oculomotor vermis, the uvula-nodulus, and the ansiform lobule are more or less independent components of the visuomotor cerebellum that are involved in different corticocerebellar and/or brain stem olivocerebellar loops. The floccular lobe and the oculomotor vermis share different mossy fiber inputs from the brain stem; the dorsal paraflocculus and the ansiform lobule receive corticopontine mossy fibers from postrolandic visual areas and the frontal eye fields, respectively. Of the visuomotor functions of the cerebellum, the vestibulo-ocular reflex is controlled by the floccular lobe; saccadic eye movements are controlled by the oculomotor vermis and ansiform lobule, while control of smooth pursuit involves all these cerebellar visuomotor regions. Functional imaging studies in humans further emphasize cerebellar involvement in visual reflexive eye movements and are discussed.

Inferior olive and oculomotor system

Three subnuclei within the inferior olive are implicated in the control of eye movement; the dorsal cap (DC), the beta-nucleus and the dorsomedial cell column (DMCC). Each of these subnuclei can be further divided into clusters of cells that encode specific parameters of optokinetic and vestibular stimulation. DC neurons respond to optokinetic stimulation in one of three planes, corresponding to the anatomical planes of the semicircular canals. Neurons in the beta-nucleus and DMCC respond to vestibular stimulation in the planes of the vertical semicircular canals and otoliths. Each these olivary nuclei receives excitatory and inhibitory signals from pre-olivary structures. The DC receives excitatory signals from the ipsilateral nucleus of the optic tract (NOT) and inhibitory signals from the contralateral nucleus prepositus hypoglossi (NPH). The beta-nucleus and DMCC receive inhibitory signals from the ipsilateral nucleus parasolitarius (Psol) and excitatory signals from the contralateral dorsal Y group. Consequently, the olivary projection to the cerebellum, although totally crossed, still represents bilateral sensory stimulation. Inputs to the inferior olive from the NOT, NPH, Psol or Y-group discharge at frequencies of 10-100 imp/s. CFRs discharge at 1-5 imp/s; a frequency reduction of an order of magnitude. Inferior olivary projections to the contralateral cerebellum are sagittally arrayed onto multiple cerebellar folia. These arrays establish coordinate systems in the flocculus and nodulus, representing head-body movement. These climbing fiber-defined spatial coordinate systems align Purkinje cell discharge onto subjacent cerebellar and vestibular nuclei. In the oculomotor system, olivo-cerebellar circuitry enhances and modifies eye movements based on movement of the head-body in space.

Oculomotor cerebellum

The anatomical, physiological, and behavioral evidence for the involvement of three regions of the cerebellum in oculomotor behavior is reviewed here: (1) the oculomotor vermis and paravermis of lobules V, IV, and VII; (2) the uvula and nodulus; (3) flocculus and ventral paraflocculus. No region of the cerebellum controls eye movements exclusively, but each receives sensory information relevant for the control of multiple systems. An analysis of the microcircuitry suggests how sagittal climbing fiber zones bring visual information to the oculomotor vermis; convey vestibular information to the uvula and nodulus, while optokinetic space is represented in the flocculus. The mossy fiber projections are more heterogeneous. The importance of the inferior olive in modulating Purkinje cell responses is discussed.

Cardiovascular modules in the cerebellum

Mapping with local lesions, electrical or chemical stimulation, or recording evoked field potentials or unit spikes revealed localized representations of cardiovascular functions in the cerebellum. In this review, which is based on literatures in the field (including our own publications), I propose that the cerebellum contains five distinct modules (cerebellar corticonuclear microcomplexes) dedicated to cardiovascular control. First, a discrete rostral portion of the fastigial nucleus and the overlying medial portion of the anterior vermis (lobules I, II and III) conjointly form a module that controls the baroreflex. Second, anterior vermis also forms a microcomplex with the parabrachial nucleus. Third, a discrete caudal portion of the fastigial nucleus and the overlying medial portion of the posterior vermis (lobules VII and VIII) form another module controlling the vestibulosympathetic reflex. Fourth, the medial portion of the uvula may form a module with the nucleus tractus solitarius and parabrachial nucleus. Fifth, the lateral edge of the nodulus and the uvula, together with the parabrachial nucleus and vestibular nuclei, forms a cardiovascular microcomplex that controls the magnitude and/or timing of sympathetic nerve responses and stability of the mean arterial blood pressure during changes of head position and body posture. The lateral nodulus-uvula appears to be an integrative cardiovascular control center involving both the baroreflex and the vestibulosympathetic reflex.

Molecular, topographic, and functional organization of the cerebellar cortex: a study with combined aldolase C and olivocerebellar labeling

Aldolase C (zebrin) expression in Purkinje cells reveals stripe-shaped compartments in the cerebellar cortex. However, it is not clear how these compartments are related to cerebellar functional localization. Therefore, we identified olivocerebellar projections to aldolase C compartments by labeling climbing fibers with biotinylated dextran injected into various small areas within the inferior olive in rats. Specific rostral and caudal aldolase C compartments were linked in an orderly manner by common olivocerebellar projection across the rostrocaudal boundary on lobule VIc-crus Ib. Based on the localization of the olivary origins of projection to similar compartments, the compartments and olivocerebellar projections could be sorted into five groups: group I, positive compartments extending from the posterior lobe to the anterior lobe innervated by the principal olive and some neighboring areas; group II, positive compartments localized within the posterior lobe innervated by several medial subnuclei; group III, vermal and central negative compartments innervated by the centrocaudal medial accessory olive; group IV, negative and lightly positive compartments in the hemisphere and the rostral and caudal pars intermedia innervated by the dorsal accessory olive and some neighboring areas; group V, the flocculus and nodulus. The olivocerebellar topography within each group was simple and suggests an "orientation axis" within the concerned parts of the inferior olive. Furthermore, parts of the inferior olive in each group receive specific afferent inputs, indicating a close relationship between aldolase C compartments and functional localization. Thus, the five-group scheme we propose here may integrate the molecular, topographic, and functional organization of the cerebellum.

Cerebellar climbing fibers modulate simple spikes in Purkinje cells

Purkinje cells have two action potentials: Climbing fiber responses (CFRs) and simple spikes (SSs). CFRs reflect the discharge of a single climbing fiber at multiple synaptic sites on the proximal dendrite of the Purkinje cell. SSs reflect the summed action of a subset of parallel fiber synapses on Purkinje cell dendritic spines. Because mossy fiber afferents terminate on granule cells, the ascending axons of which bifurcate, giving rise to parallel fibers, the modulation of SSs has been attributed to mossy fiber afferent signals. This inference has never been tested. Conversely, the low discharge frequency of CFRs has led many to conclude that they have a unique and intermittent role in cerebellar signal processing. We examine the relative potency of vestibularly modulated mossy fiber and climbing fiber signals in evoking CFRs and SSs in Purkinje cells of the uvula-nodulus in chloralose-urethane-anesthetized rabbits. Vestibular primary afferents were blocked by unilateral labyrinthectomy (UL). A UL destroys the vestibular primary afferent signal to the ipsilateral uvula-nodulus, while leaving intact the vestibular climbing fiber signal from the contralateral inferior olive. After UL, vestibular stimulation modulated CFRs and SSs in ipsilateral uvula-nodular Purkinje cells, demonstrating that the primary vestibular afferent mossy fiber input to the ipsilateral uvula-nodulus was not necessary for SS modulation. Unilateral microlesions of the caudal half of the beta-nucleus of the inferior olive reduced a modulated climbing fiber signal to the contralateral uvula-nodulus, causing loss of both vestibularly modulated CFRs and SSs in contralateral Purkinje cells. Vestibular climbing fibers not only evoke low-frequency CFRs, but also indirectly modulate higher-frequency SSs. This modulation must be attributed to cerebellar interneurons. Golgi cell inhibition of granule cells may provide the interneuronal mechanism for CFR-induced SS modulation.

Vestibular signals in the parasolitary nucleus

Vestibular primary afferents project to secondary vestibular neurons located in the vestibular complex. Vestibular primary afferents also project to the uvula-nodulus of the cerebellum where they terminate on granule cells. In this report we describe the physiological properties of neurons in a "new" vestibular nucleus, the parasolitary nucleus (Psol). This nucleus consists of 2,300 GABAergic neurons that project onto the ipsilateral inferior olive (beta-nucleus and dorsomedial cell column) as well as the nucleus reticularis gigantocellularis. These olivary neurons are the exclusive source of vestibularly modulated climbing fiber inputs to the cerebellum. We recorded the activity of Psol neurons during natural vestibular stimulation in anesthetized rabbits. The rabbits were placed in a three-axis rate table at the center of a large sphere, permitting vestibular and optokinetic stimulation. We recorded from 74 neurons in the Psol and from 23 neurons in the regions bordering Psol. The activity of 72/74 Psol neurons and 4/23 non-Psol neurons was modulated by vestibular stimulation in either the pitch or roll planes but not the horizontal plane. Psol neurons responded in phase with ipsilateral side-down head position or velocity during sinusoidal stimulation. Approximately 80% of the recorded Psol neurons responded to static roll-tilt. The optimal response planes of evoked vestibular responses were inferred from measurement of null planes. Optimal response planes usually were aligned with the anatomical orientation of one of the two ipsilateral vertical semicircular canals. The frequency dependence of null plane measurements indicated a convergence of vestibular information from otoliths and semicircular canals. None of the recorded neurons evinced optokinetic sensitivity. These results are consistent with the view that Psol neurons provide the vestibular signals to the inferior olive that eventually reached the cerebellum in the form of modulated climbing fiber discharges. These signals provide information about spatial orientation about the longitudinal axis.

Fos expression in the rat brain after exposure to gravito-inertial force changes

The immediate-early genes constitute useful neurobiological tools for mapping brain functional activity after sensory stimulation. We immunohistochemically investigated Fos protein expression in the brain of rats exposed to gravito-inertial force changes. Experiments were performed in hypergravity rats born and housed for 60 days in terrestrian gravity (1xg) and thereafter exposed for 90 min to 2xg or 4xg in a centrifuge, and in hypogravity rats born and housed for 60 days at 2xg and submitted for 90 min to 1xg. Data from these two experimental groups were quantified by light microscopy and compared to those from two groups of control rats born and permanently housed in either 1xg or 2xg environments that never had to adapt to novel gravito-inertial environments. Results showed a low basal Fos expression in the controls and a strong Fos staining in the experimental rats. Only the hypergravity rats displayed Fos-positive cells in vestibular-related brainstem regions (medial, inferior, and superior vestibular nuclei (VN); group y; dorsomedial cell column (DMCC) of the inferior olive (IO)). By contrast, many suprabulbar areas were strongly labeled in both the hyper- and hypogravity rats, as shown by the numerous Fos-positive cells in mesencephalic (colliculus, laterodorsal periaqueductal gray, autonomic nuclei), diencephalic (hypothalamic and thalamic nuclei), and telencephalic (parietal, temporal, entorhinal and visual cortices) structures. These spatial patterns of Fos expression suggest that an increase in gravito-inertial force activates otolith-vestibulo-olivar pathways and various suprabulbar structures underlying the corticovestibular interactions, which govern the multiple representations of vestibular information in the cortex. A decrease in gravito-inertial force has the opposite effects on the vestibulo-olivar structures as a result of otolith system disfacilitation which, in turn, modifies the activity of complex neural pathways. Exposure to both hyper- and hypogravity environments likely induces neurovegetative and/or stress effects that could account for Fos labeling in autonomic nuclei and in nervous structures involved in the hypothalamo-pituitary-adrenal axis.

A review of otolith pathways to brainstem and cerebellum

Our knowledge of otolith pathways is developing rapidly, but is still far from complete. Primary afferents from the sacculus and utricle terminate mainly in the lateral, inferior and caudal superior vestibular nuclei, and the ventral cerebellum, in particular the nodulus. Otolith signals descend via reticulo- and vestibulospinal pathways in the spinal cord to influence neck motoneurons and ascending proprioceptive afferents. Utricular information can reach the extraocular eye muscles via mono-, di-, and multisynaptic pathways, but saccular afferents probably only by multisynaptic pathways. The otolith signals are relayed from the vestibular nuclei, medullary reticular formation, inferior olive, and lateral reticular nucleus to sagittal zones in the caudal cerebellar vermis (nodulus and uvula), and influence the deep cerebellar nuclei. The graviceptive information could be channeled by the cerebellar efferents back to the vestibular and inferior olive complex, or fed into ascending pathways that would innervate the mescencephalon, the thalamus, and cerebral cortex.

Parasolitary nucleus: a source of GABAergic vestibular information to the inferior olive of rat and rabbit

At least two subnuclei of the inferior olive, the beta-nucleus, and the dorsomedial cell column (dmcc), contain vestibularly responsive neurons that receive a dense descending projection that uses gamma-aminobutyric acid (GABA) as the transmitter. In contrast to the GABAergic innervation of other olivary subnuclei, the terminal boutons that terminate on neurons in the beta-nucleus and the dorsomedial cell column remain intact after cerebellectomy, ruling out both the cerebellum and the cerebellar nuclei as afferent sources. By using both immunohistochemical as well as orthograde and retrograde tracer methods, we have identified the source of the GABAergic pathway to the beta-nucleus and dmcc in both rat and rabbit. Under physiologic recording of single olivary neurons to guide electrode placement, we injected the bidirectional tracer, wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) into the beta-nucleus and dmcc of the inferior olive. These injections retrogradely labeled neurons in the parasolitary nucleus (Psol) near the vestibular complex. Psol neurons were identified as GABAergic with an antibody to glutamic acid decarboxylase (GAD). In the rat, Psol neurons are small (5-7 microm in diameter) and number approximately 1,800. In the rabbit, they are slightly larger (6-9 microm in diameter) and number approximately 2,200. WGA-HRP injections in conjunction with GAD immunohistochemistry double labeled a high percentage of neurons in both the rat and rabbit Psol. Injection of the orthograde tracer Phaseolus vulgaris-leucoagglutinin into the area of the Psol revealed a projection from this region to both the beta-nucleus and dmcc. Subtotal electrolytic lesions of this division of the Psol caused a substantial reduction in GAD-positive synaptic terminals in both the ipsilateral beta-nucleus and dmcc. The location of these GABAergic neurons, bordering both the nucleus solitarius and caudal vestibular complex, emphasizes the importance of the Psol in the processing of both vestibular and autonomic information pertinent to postural control.

Topography and reciprocal activity of cerebellar Purkinje cells in the uvula-nodulus modulated by vestibular stimulation

In the rabbit uvula-nodulus, vestibular and optokinetic information is mapped onto parasagittal zones by climbing fibers. These zones are related functionally to different pairs of vertical semicircular canals, otolithic inputs and horizontal optokinetic inputs. Vestibular stimulation restricted to one of these zones modulates climbing fiber responses (CFRs). Within each of these zones, simple spikes (SSs) are modulated reciprocally with CFRs. In rabbits anesthetized with chloralose-urethan, we have used vestibular and optokinetic stimulation to evoke CFRs within a parasagittal zone while recording from Purkinje cells in adjacent zones. We have examined whether the CFRs evoked by vestibular stimulation in one zone influence the SSs of an adjacent zone. CFRs and SSs were recorded during roll vestibular stimulation. The orientation of the head of the rabbit with respect to the axis of rotation was varied systematically so that a climbing fiber null plane could be determined. This null plane was the orientation of the head about the vertical axis at which no modulation of the CFR was observed during rotation about the longitudinal axis of the vestibular rate table. In the left uvula-nodulus, a medial sagittal strip extending through all the folia contained Purkinje cells with CFRs that had optimal planes of stimulation coplanar with the left posterior-right anterior semicircular canals (LPC-RAC). Lateral to this strip was a strip of Purkinje cells with CFRs that were characterized by optimal planes corresponding to stimulation of the left anterior-right posterior semicircular canals (LAC-RPC). SSs in Purkinje cells were modulated out of phase with CFRs from the same Purkinje cell. The depth of modulation of both CFRs and SSs was reduced during rotation in the climbing fiber "null plane". The depth of modulation of SSs was greatest when recorded from Purkinje cells located at the center of semicircular canal-related strip. We observed that 1) all folia of the uvula-nodulus receive vestibular climbing fiber inputs; 2) these climbing fiber inputs convey information from the vertical semicircular canals and otoliths but not the horizontal semicircular canals; 3) CFRs evoked in a particular sagittal zone do not influence SSs in adjacent zones; 4) modulation of a CFRs in a particular Purkinje cell can occur without modulation of SSs in the same Purkinje cell, although modulation of SSs was not observed in the absence of CFR modulation; and 5) modulation of SSs sometimes preceded that of CFRs in the same cell, implying that interneuronal pathways may contribute to SS modulation. Climbing fiber-driven Golgi cells, the inhibitory axon terminals of which end on granule cell dendrites in the classic glomerular synapse, may provide this interneuronal mechanism.

Saccule contribution to immediate early gene induction in the gerbil brainstem with posterior canal galvanic or hypergravity stimulation

Immunolabeling patterns of the immediate early gene-related protein Fos in the gerbil brainstem were studied following stimulation of the sacculus by both hypergravity and galvanic stimulation. Head-restrained, alert animals were exposed to a prolonged (1 h) inertial vector of 2 G (19.6 m/s2) head acceleration directed in a dorso-ventral head axis to maximally stimulate the sacculus. Fos-defined immunoreactivity was quantified, and the results compared to a control group. The hypergravity stimulus produced Fos immunolabeling in the dorsomedial cell column (dmcc) of the inferior olive independently of other subnuclei. Similar dmcc labeling was induced by a 30 min galvanic stimulus of up to -100 microA applied through a stimulating electrode placed unilaterally on the bony labyrinth overlying the posterior canal (PC). The pattern of vestibular afferent firing activity induced by this galvanic stimulus was quantified in anesthetized gerbils by simultaneously recording from Scarpa's ganglion. Only saccular and PC afferent neurons exhibited increases in average firing rates of 200-300%, suggesting a pattern of current spread involving only PC and saccular afferent neurons at this level of stimulation. These results suggest that alteration in saccular afferent firing rates are sufficient to induce Fos-defined genomic activation of the dmcc, and lend further evidence to the existence of a functional vestibulo-olivary-cerebellar pathway of adaptation to novel gravito-inertial environments.

A retrograde double-labeling technique for light microscopy. A combination of axonal transport of cholera toxin B-subunit and a gold-lectin conjugate

A light microscopical, non-fluorescent, retrograde double-labeling technique is described. Cholera toxin B-subunit (CTb) and a conjugate of wheatgerm agglutinin and bovine serum albumin coupled to 10 nm gold particles (gold-lectin) are both excellent retrograde tracers and, when visualized by means of immunohistochemistry and silver intensification, respectively, may be readily identified within the same cell. This light microscopical retrograde double-labeling technique is illustrated in rat with experiments designed to investigate the collateralisation (1) of vestibular neurons to the spinal cord and oculomotor complex, (2) of spinal neurons to the left and right lateral reticular nucleus, and (3) of inferior olivary neurons to the uvula of the cerebellum. Advantages over fluorescent double-labeling experiments are found in the fact that the diaminobenzidine reaction product as well as the silver/gold deposits do not fade and can be examined in counterstained sections. Moreover, the injection sites can be kept quite small and may be guided by electrophysiological recording through the injection pipette.

Zonal organization of the climbing fiber projection to the flocculus and nodulus of the rabbit: a combined axonal tracing and acetylcholinesterase histochemical study

The localization and termination of olivocerebellar fibers in the flocculus and nodulus of the rabbit were studied with anterograde axonal transport methods [wheatgerm agglutinin-horseradish peroxidase (WGA-HRP) and tritiated leucine] and correlated with the compartments in the white matter of these lobules delineated with acetylcholinesterase histochemistry (Tan et al. J. Comp. Neurol., 1995, this issue). Olivocerebellar fibers originating from the caudal dorsal cap travel through floccular compartments FC2 and FC4 to terminate as climbing fibers in floccular zones FZII and FZIV. Fibers from the rostral dorsal cap and the ventrolateral outgrowth traverse compartments FC1 and FC3, which are interleaved with compartments FC2 and FC4, and terminate in zones FZI and FZIII. Fibers from the rostral pole of the medial accessory olive traverse the C2 compartment and terminate in the C2 zone. FZI-III extend into the adjoining folium (folium p) of the ventral paraflocculus. The C2 zone continues across folium p into other folia of the ventral paraflocculus and into the dorsal paraflocculus. Four compartments and five zones were distinguished in the nodulus. Medial compartment XC1 contains olivocerebellar fibers from the caudal dorsal cap and subnucleus beta that terminate in the XZI zone. Olivocerebellar fibers from the rostral dorsal cap and the ventrolateral outgrowth occupy XC2 and terminate in XZII. The XC4 compartment contains fibers from both the caudal dorsal cap and from the rostral dorsal cap and the ventrolateral outgrowth. The latter terminate in a central portion of the XZIV zone. The dorsomedial cell column projects to the XZIII zone, which is present only in the dorsal part of the nodulus. The rostral medial accessory olive projects to the XZV zone, which occupies the lateral border of the nodulus. These results confirm and extend the conclusions of Katayama and Nisimaru ([1988] Neurosci. Res. 5:424-438) on the zonal pattern in the olivo-nodular projection in the rabbit. Additional observations were made on the presence of a lateral A zone (Buisseret-Delmas [1988] Neurosci. Res. 5:475-493) in the hemisphere of lobules VI and VII. Retrograde labeling of the nucleo-olivary tract of Legendre and Courville ([1987] Neuroscience 21:877-891) was observed after WGA-HRP injections into the inferior olive including the rostral dorsal cap and the ventrolateral outgrowth. The anatomical and functional implications of these observations are discussed.

Projection of cardiovascular afferents to the lateral nodulus-uvula of the cerebellum in rabbits

Vagal and aortic afferent projections to the nodulus and uvula of the cerebellar vermis were examined in anesthetized and paralysed rabbits. Electrical stimulations of vagal and aortic nerves at a frequency of 1/s produced field potentials in the lateral cortical region of the contralateral nodulus-uvula with a latency of 6.5-19 ms. These potentials were negative in the molecular layer and positive in the granular layer. At a higher stimulation rate (30/s), these potentials were reduced by 60-65% of the control value. These results indicate that the lateral cortical region of the nodulus-uvula receives contralateral vagal and aortic afferent signals via climbing fibers. Electrical stimulation of vagal nerves also produced field potentials in the lateral region of the ipsilateral nodulus-uvula with a latency of 6-10.5 ms. Their laminal profile was characteristic of mossy fiber responses. At a higher stimulation rate (30/s), the reduction of these potentials was only 35%. Thus the lateral nodulus-uvula also receives the ipsilateral vagal afferent signals via mossy fibers. Following injection of horseradish peroxidase into the small areas of the lateral nodulus, labeled cells were found in bilateral intercalatus nucleus, prepositus hypogrossal nucleus, Roller nucleus, medial fascicullus longitudinalis, and medial and lateral vestibular nuclei. These nuclei may contain precerebellar neurons in the pathway from the vagal nerve to the lateral nodulus-uvula via mossy fibers.

Distribution of corticotropin-releasing factor and calcitonin gene-related peptide in the developing mouse cerebellum

Corticotropin-releasing factor (CRF)-like immunoreactive (IR) fibers were investigated ontogenically in the mouse cerebellum. CRF-IR was detected in the climbing fiber and mossy fibers as in other species. In addition, CRF-IR dense fiber plexuses were detected from postnatal day (PD) 2 to 9, in the developing Purkinje cell layer of the vermal lobules, paraflocculus, flocculus and crus 1 ansiform lobule, gradually forming a pericellular nest around the Purkinje cell somata. Immunoelectron-microscopical analysis showed that dense fibers made synaptic contacts with the Purkinje cell somata on PD 7. In the lobules mentioned above, CRF-IR dense fibers showed parasagittal banded patterns. Calcitonin gene-related peptide (CGRP)-IR showed similar fiber bands at these stages. Interestingly, these two patterns of peptidergic fiber bands were complementary in distribution. From around PD 9, CRF-IR fibers lost the immunoreactive dots in the Purkinje cell layer. Immunoreactivity at this stage was observed in the axons projecting to the molecular layer, and thin CRF-IR fibers began to appear in the neighboring area. Numerous typical climbing fiber-like CRF-IR fibers were found throughout the cerebellar cortex from PD 16 to adult. The inferior olivary complex (the origin of climbing fibers) appears to be the origin of these dense fiber plexuses as CRF-IR cells were already present from PD 2 in the dorsal cap nucleus, beta subnucleus and caudomedial part of the accessory olivary nucleus. No neurons containing both CRF and CGRP immunoreactivities were observed. These results suggest that CGRP- and CRF-IR developing climbing fibers innervate different compartments of Purkinje cells, especially in the vestibular cerebellar cortex in mice. Furthermore, CRF-IR fibers gradually changed to become typical climbing fibers, while CGRP-IR disappeared altogether.

Origins of cerebellar mossy and climbing fibers immunoreactive for corticotropin-releasing factor in the rabbit

Corticotropin-releasing factor (CRF) has been implicated by both anatomical and physiological techniques as a potential cerebellar transmitter or modulator. In the present experiment, with the aid of immunohistochemistry, we have described specific cerebellar afferent pathways in the rabbit in which CRF is located. CRF-immunoreactive climbing fibers were present in the molecular layer throughout the cerebellum, but especially in lobules 8-9a. All inferior olivary neurons were CRF-immunoreactive. In lobules 8-9a, CRF-immunoreactive mossy fibers were organized in sagittal bands. The highest density of CRF-immunoreactive mossy fiber terminals was observed in the granule cell layer of lobules 8-9a and the flocculus. No CRF-immunoreactive perikarya were located in rabbit cerebellum. The brainstem origin of CRF-immunoreactive mossy fiber terminals was suggested by numerous CRF-immunoreactive perikarya located in the medial, lateral and descending vestibular nuclei, nucleus prepositus hypoglossi, nucleus x, paramedian reticular nucleus, gigantocellular reticular nucleus, lateral reticular nucleus, and raphé nuclei. Using double label experiments, we investigated the specific CRF afferent projection to the flocculus and posterior vermis. Horseradish peroxidase (HRP) injections into the posterior vermis double labeled CRF-immunoreactive neurons in the caudal medial and descending vestibular nuclei and nucleus prepositus hypoglossi. HRP injections into the flocculus double labeled more CRF-immunoreactive neurons in the nucleus prepositus hypoglossi than in the vestibular nuclei. HRP injections into either the posterior vermis or flocculus double labeled CRF-immunoreactive neurons in the paramedian reticular nucleus, nucleus reticularis gigantocellularis, and raphé nuclei. These data suggest that CRF may play an important role in vestibularly related functions of the cerebellum.

Activation of a specific vestibulo-olivary pathway by centripetal acceleration in rat

Unanesthetized Long-Evans (pigmented) rats were subjected to 2.0 G centripetal acceleration for 90 min. Immunohistochemical analysis, using a polyclonal antibody for Fos, revealed a distinct pattern of neuronal activation in the off-axis animals in the dorsomedial cell column (DMCC) of the inferior olivary nucleus. These results are consistent with previous anatomical evidence and indicate that the DMCC is an important component in an otolith-olivocerebellar circuit which may help to define an internal spatial reference.

Topographic and zonal pattern of olivocerebellar projection to the paramedian lobule in the rabbit: an experimental study with an HRP retrograde tracing method

Distribution of neurons in the inferior olive (IO) projecting to the paramedian lobule (PML) was studied in rabbits by means of retrograde transport of horseradish peroxidase (HRP). HRP was injected into various regions of different folia of the PML. Findings indicate zonal and to some extent topographic organization in olivocerebellar projections to PML folia. The neurons in corresponding areas of dorsal (dlPO) and ventral lamina (vlPO) of the principal olive (PO) project to composite zones D (D1 + D2) in sublobule f: medial, intermediate and lateral. In addition, the caudal part of the medial accessory olive (MAO) projects to the most laterally located zone (C2-lateral) and the caudal part of the dorsal accessory olive (DAO) to the most lateral zone (C3) in sublobule f. The middle part of the DAO sends projections to zone C1 located medially in sublobules d-a. The rostral and caudal parts of the DAO send projections to zone C3 in sublobules a and f, respectively. The rostral, middle and adjacent caudal parts of MAO, with no clear topographic organization, project to broad zone C2 in sublobules e-b. The neurons in restricted areas of the caudomedial part of the dlPO and vlPO, probably intermingled with those supplying the composite medial zone D in sublobule f, project to sublobules e-b to terminate in zones D1 and D2, respectively.

Ontogenesis of enkephalinergic afferent systems in the opossum cerebellum

Enkephalin (ENK) immunoreactive climbing fibers, mossy fibers and a beaded plexus of axons are present in the adult opossum's cerebellar cortex. We have used the indirect antibody peroxidase-antiperoxidase technique to study the ontogeny of enkephalinergic axons in the cerebellum of pouch young opossums from postnatal day (PD) 1 to PD 83. On PD 1, ENK axons are present in the intermediate layer of the cerebellar anlage. At PD 18, after a period of 'waiting', ENK fibers form clusters throughout the cerebellar cortex primarily within the nascent Purkinje cell layer. By PD 40, axon terminals with a climbing fiber phenotype circumscribe Purkinje cells; immature mossy fiber rosettes are present within the internal granule cell layer. A third axon phenotype, beaded ENK fibers can be distinguished on PD 68. Between PD 40 and PD 68, the distributions of ENK climbing and mossy fibers overlap in vermal lobules II-VIII and X, whereas in the hemispheres climbing fibers predominate. However, by PD 83, ENK positive climbing fibers are no longer evident in lateral folia. These results indicate that early arriving ENK axons are present before the differentiation of their cellular targets. Further, a transient appearance of ENK in discrete populations of developing climbing fibers suggests several developmental events: (1) cell death in the inferior olive, (2) collateral regression, or (3) a transient expression of this peptide, that may be characteristic of this chemically defined system of axons.

Zonal organization of climbing fiber projections to the uvula in the cat

Climbing fiber projections from the inferior olive to the uvula of the cerebellum were studied in the cat by using retrograde axonal transport of horseradish peroxidase. Following large and small injections into various parts of the uvula, the distribution of labeled cells in the inferior olive was investigated. The findings indicate six longitudinal zones extending throughout the dorsal and ventral uvula: the caudal part of the nucleus beta projects to a most medially located zone (caudal beta zone) with a width of about 0.4 mm; the rostral part of the nucleus beta projects to a zone located at about 0.6 mm from the midline (rostral beta zone); the caudal part of the medial accessory olive (MAO) projects to a zone (caudal MAO zone) located lateral to the rostral beta zone; the dorsomedial cell column projects to a zone (dorsomedial cell column zone) located in the intermediate part of the uvula at about 1.2 mm from the lateral edge of the uvula; the ventral lamella of the principal olive (PO) projects to a zone (ventral lamella of PO zone) about 0.7 mm from the lateral edge of the uvula; finally, the rostral part of the MAO projects to the most lateral zone (rostral MAO zone). These conclusions are in general agreement with those of earlier studies and also provide a more detailed zonal configuration of climbing fiber projections to the uvula.

Parasagittal zonal pattern of olivo-nodular projections in rabbit cerebellum

Injection of horseradish peroxidase (HRP) into the nodulus of the rabbit retrogradely labeled cells in 5 subdivisions of the contralateral inferior olive. Localized HRP injections at each of the medial, intermediate and lateral parts of the nodulus revealed 6 longitudinal zones, two zones in each part, projected differentially from the 5 olivary subdivisions: (i) the medial-most zone projected from the beta nucleus, (ii) the lateral zone of the medial part and (iii) the lateral zone of the intermediate part both from the dorsal cap, (iv) the medial zone of the intermediate part from the ventrolateral outgrowth, (v) the medial zone of the lateral part from the dorsomedial cell column, and (vi) the lateral-most zone from the rostrolateral part of the medial accessory olive. A complication is that the zones (v) and (vi) seemed to cover the dorsal lamina of the nodulus, but not the ventral lamina. The lateral part of the ventral nodulus seemed to be projected from the dorsal cap and may therefore be a lateral extension of zone (iv). There was an indication that the rostral-most area of the medial accessory olive also projects to the nodulus, but a specific receptive zone for this projection was unclear. The present results suggest that the small lateral area of the nodulus previously found to be involved in cardiovascular control is projected from the rostrolateral part of the medial accessory olive and/or the dorsomedial cell column.

Zonal organization of olivo-nodulus projections in albino rabbits

The organization of inferior olivary projections to the cerebellar nodulus in albino rabbits was assessed by autoradiographic, anterograde degeneration and retrograde transport techniques. These data indicate that the caudal aspect of the dorsal cap of Kooy projects to a band extending 0.5-1 mm lateral to the midline of the nodulus. The medial half of this region receives a projection from beta nucleus over at least the dorsal surface of the nodulus; an extension onto the ventral surface, though, is consistent with the anterograde tracing data. The rostral aspect of the dorsal cap and ventrolateral outgrowth projects to an adjacent 0.5-1 mm wide band in the nodulus. A group of cells spanning the intermediocaudal dorsal cap and the adjacent, dorsomedial margin of the beta nucleus appears to project laterally on the ventral surface of the nodulus. On the dorsal aspect of the nodulus and ventral surface of lobule IXd, though, comparisons of anterograde and retrograde tracing data suggest that this lateral field is innervated by the rostral aspect of the dorsomedial cell column and the rostromedial accessory olive. Finally, the regions of lobules X and IXd lining the posterolateral fissure represent a transition between lobule IX and ventral lobule X patterns of olivary projections. These data provide a basis for investigating the efferent projections of the nodulus to distinct olivo-vestibular terminal fields in the vestibular nuclei.

Topographic and zonal organization of the olivocerebellar projection in the reeler mutant mouse

The organization of the olivocerebellar projection in the homozygous reeler mouse (rl/rl) was studied with the use of microinjections of 3H-leucine in different regions of the inferior olivary complex (IO) or horseradish peroxidase conjugated with wheat germ agglutinin (WGA-HRP) into medial, intermediate, or lateral regions of the reeler cerebellum. The purpose of this investigation was to determine the pattern of termination of olivocerebellar climbing fibers (CFs) in the cerebellum via an anterograde tracing technique, and to determine the topographic organization of the olivocerebellar projection via both anterograde and retrograde methods. The inferior olive injections were made via the ventral (i.e., retropharygeal) approach to the IO to minimize diffusion into other brainstem precerebellar nuclei and thus to ensure accurate well-restricted, injection sites. Labeled CF terminals were seen in both the superficial Purkinje cell (PC) layer (normally positioned PCs) and around PCs in the granular layer and central masses (ectopic PCs). The pattern of labeling is suggestive of orthogonal organization, in that vertical columns of cells are labeled. This is especially apparent in the medial PC group, where at least three bands are identified. Within an orthogonal band, CF terminals are seen around both superficial and deep Purkinje cells. Our data indicate that olivocerebellar topography is generally similar in reeler and normal mice despite severe abnormalities in target cell position in the reeler. The medial cerebellar region receives input from the caudal two-fifths of the medial accessory olive (MAO). The intermediate PC cluster receives input from more rostral portions of all three olivary divisions (MAO, principal olive [PO] and dorsal accessory olive [DAO] ), while rostral portions of MAO and PO project to the lateral cerebellum. These results indicate that the zonal organization of the olivocerebellar projection in the adult reeler exhibits a pattern generally similar to that seen in normal mice. This suggests that an afferent system can develop a normal organization despite having ectopic targets.

Topographical distribution of Purkinje cells in the uvula and the nodulus projecting to the vestibular nuclei in cats

The localization of the Purkinje cells in the uvula and nodulus projecting to the vestibular nuclei and the prepositus hypoglossal nucleus (PH) was studied by means of retrograde axonal transport of horseradish peroxidase in cats. Findings indicate a zonal organization in the uvula and nodulus projecting to the vestibular nuclei as follows; the Purkinje cells located in the medial half of the uvula except for the area along the posterolateral fissure project to the middle part of the inferior vestibular nucleus (IV) (middle IV zone); those in the lateral half of the uvula other than the laterocaudal part project to the caudal part of the IV (caudal IV zone); those in the mediorostral part of the nodulus and the middle part of the nodulus project to the middle part of the medial vestibular nucleus (MV) (middle MV zone); those in the lateral part of the nodulus project to the caudal part of the MV (caudal MV zone); those in the medial part of the uvula and nodulus along the posterolateral fissure project to the dorsal peripheral part of the superior vestibular nucleus (SV) (SV zone). There is no specific projection zone in the uvula and nodulus projecting to the lateral vestibular nucleus, the ventral peripheral and the central part of the SV, the rostral part of the MV, the rostral part and the caudal pole of the IV, the caudal one-third of the group f, the group x and the PH.

Purification of specific antibody against aspartate and immunocytochemical localization of aspartergic neurons in the rat brain

The distribution of L-aspartate known as a putative excitatory neurotransmitter in the central nervous system was investigated immunocytochemically in the rat brain. Anti-aspartate antiserum was raised in rabbits using L-aspartate covalently conjugated to rabbit serum albumin with glutaraldehyde as the immunogen and was found to be cross-reactive with an L-glutamate conjugate. Monospecific anti-L-aspartate antibody was successfully purified using affinity gels coupled with several amino acids including L-aspartate and L-glutamate and with the L-glutamate conjugate. Putative aspartergic neurons were generally immunoreactive to the purified antibody, but epithelia of the choroid plexus were also stained. These results show that the antibody is a useful tool for the immunocytochemical demonstration of possible aspartergic neurons in the central nervous system, although the immunochemical expression of L-aspartate not used as a neurotransmitter must be taken into consideration.