Parasagittal organization of the rat cerebellar cortex: direct comparison of Purkinje cell compartments and the organization of the spinocerebellar projection

Purkinje cell compartmentation as revealed by Zebrin II expression in the cerebellar cortex of pigeons (Columba livia)

Purkinje cells in the cerebellum express the antigen zebrin II (aldolase C) in many vertebrates. In mammals, zebrin is expressed in a parasagittal fashion, with alternating immunopositive and immunonegative stripes. Whether a similar pattern is expressed in birds is unknown. Here we present the first investigation into zebrin II expression in a bird: the adult pigeon (Columba livia). Western blotting of pigeon cerebellar homogenates reveals a single polypeptide with an apparent molecular weight of 36 kDa that is indistinguishable from zebrin II in the mouse. Zebrin II expression in the pigeon cerebellum is prominent in Purkinje cells, including their dendrites, somata, axons, and axon terminals. Parasagittal stripes were apparent with bands of Purkinje cells that strongly expressed zebrin II (+ve) alternating with bands that expressed zebrin II weakly or not at all (-ve). The stripes were most prominent in folium IXcd, where there were seven +ve/-ve stripes, bilaterally. In folia VI-IXab, several thin stripes were observed spanning the mediolateral extent of the folia, including three pairs of +ve/-ve stripes that extended across the lateral surface of the cerebellum. In folium VI the zebrin II expression in Purkinje cells was stronger overall, resulting in less apparent stripes. In folia II-V, four distinct +ve/-ve stripes were apparent. Finally, in folia I (lingula) and X (nodulus) all Purkinje cells strongly expressed zebrin II. These data are compared with studies of zebrin II expression in other species, as well as physiological and neuroanatomical studies that address the parasagittal organization of the pigeon cerebellum.

Genome-wide atlas of gene expression in the adult mouse brain

Molecular approaches to understanding the functional circuitry of the nervous system promise new insights into the relationship between genes, brain and behaviour. The cellular diversity of the brain necessitates a cellular resolution approach towards understanding the functional genomics of the nervous system. We describe here an anatomically comprehensive digital atlas containing the expression patterns of approximately 20,000 genes in the adult mouse brain. Data were generated using automated high-throughput procedures for in situ hybridization and data acquisition, and are publicly accessible online. Newly developed image-based informatics tools allow global genome-scale structural analysis and cross-correlation, as well as identification of regionally enriched genes. Unbiased fine-resolution analysis has identified highly specific cellular markers as well as extensive evidence of cellular heterogeneity not evident in classical neuroanatomical atlases. This highly standardized atlas provides an open, primary data resource for a wide variety of further studies concerning brain organization and function.

Precise spatial relationships between mossy fibers and climbing fibers in rat cerebellar cortical zones

Classically, mossy fiber and climbing fiber terminals are regarded as having very different spatial distributions in the cerebellar cortex. However, previous anatomical studies have not studied these two major cerebellar inputs with sufficient resolution to confirm this assumption. Here, we examine the detailed pattern of collateralization of both types of cerebellar afferent using small injections of the bidirectional tracer cholera toxin b subunit into the posterior cerebellum. The cortical and zonal location of these injections was characterized by mapping climbing fiber field potentials, the distribution of retrogradely labeled olivary neurons, and the intrinsic zebrin pattern of Purkinje cells. Labeled climbing fiber collaterals were distributed as longitudinal strips and were always accompanied by clusters of labeled mossy fiber rosettes in the subjacent granular layer. Two- and three-dimensional reconstructions and quantitative analysis showed that mossy fibers also collateralized to other stripe-like regions usually below Purkinje cells with the same zebrin-positive or zebrin-negative characteristics as that of the injection site and associated climbing fiber collaterals. The distribution of retrogradely labeled neurons in two major sources of mossy fibers, the lateral reticular and basilar pontine nuclei, revealed interlobular and some interzonal differences. These data indicate that nonadjacent cerebellar zones, sharing the same climbing fiber input and zebrin identity, also share a common mossy fiber input. Other cerebellar cortical regions that receive collaterals from the same mossy fibers usually also have the same zebrin signature. Together with the distribution of neurons in precerebellar centers, the findings suggest a revision of the modular hypothesis for information processing in the cerebellar cortex.

From clusters to stripes: The developmental origins of adult cerebellar compartmentation

Many aspects of the adult cerebellum are organized into parasagittal stripes, including several types of neurons and prominent afferent and efferent projections. Purkinje cells are the best-studied example of parasagittal organization in the cerebellum and, in particular, zebrin II/aldolase C is the stereotypical molecular marker of Purkinje cell stripe heterogeneity in the adult. Zebrin II is a member of the so-called 'late-onset' class of parasagittal markers, which are first expressed shortly after the birth of the mouse and do not reach maturity until 2-3 weeks postnatal. In contrast, 'early-onset' pattern markers are expressed in ordered Purkinje cell clusters in the embryonic cerebellum but become expressed homogeneously shortly after birth. The approximately 10 day temporal gap between the patterned expression of early and late markers has impeded the identification of putative genealogical relationships between clusters and stripes. This review will describe Purkinje cell patterns and their transitions, and critically discuss the evidence for genealogical relationships between early and late patterns.

Corticotropin-Releasing Factor Immunoreactivity Increases in the Cerebellar Climbing Fibers in the Novel Ataxic Mutant Mouse, Pogo

The ataxic pogo mouse (pogo/pogo) is a novel neurological mutant, which was derived as an inbred strain (KJR/MsKist) from a Korean wild mouse. The pathological manifestations include a difficulty in maintaining a normal posture, the failure of inter-limb coordination and an inability to walk straight. In this study, we examined the distribution of corticotropin-releasing factor (CRF) immunoreactive cerebellar climbing fibres and their projections to tyrosine hydroxylase (TH) immunoreactive Purkinje cells in the cerebellum of the pogo mutant mouse using immunohistochemistry. In the pogo/pogo mouse, a subset of climbing fibres was stained more intensely for CRF than in the control. Moreover, ataxic pogo mouse, neurons of the inferior olivary nucleus projecting climbing fibres were also more intensely stained for CRF than in the control. In the pogo/pogo mouse, TH immunoreactivity was located in the Purkinje cells, whereas no TH expression was found in the control. Double immunostaining for CRF and TH in the pogo/pogo cerebellum revealed that the distribution of TH-immunoreactive Purkinje cells corresponded to terminal fields of CRF-immunoreactive climbing fibres but not to the CRF-immunoreactive mossy fibres. Therefore, we suggest that an increase of CRF level may alter the function of targeted Purkinje cells and that it is related to the ataxic phenotype in the pogo mutant mouse.

Neurogranin expression identifies a novel array of Purkinje cell parasagittal stripes during mouse cerebellar development

Markers that reveal the parasagittal organization of cerebellar Purkinje cells may be grouped into two classes based on the time during development when they are expressed. In mice, early-onset markers are defined by their heterogeneous expression in clusters of Purkinje cells during late embryogenesis, which disappears shortly following birth. Late-onset markers are generally not expressed until about 1 week after birth and do not reach a stable striped expression pattern until about 3 weeks postnatally. Currently, no endogenous markers are known that are heterogeneously expressed in the temporal gap between these two classes. Here we present immunocytochemical evidence that parasagittal stripes of Purkinje cells express a member of the calpacitin protein family, neurogranin, possibly from as early as embryonic day (E) 13 and definitively from E15, in a pattern that persists up to postnatal day (P) 20. Neurogranin is thus the first endogenous marker of a Purkinje cell subset capable of bridging the temporal gap between the early- and late-onset patterns. In the early neonate, up to five pairs of neurogranin-immunopositive Purkinje cell stripes run parasagittally through the cerebellum, with the exact number dependent on the rostrocaudal position. Expression is lost during postnatal development in a transverse zone-dependent fashion. Purkinje cells in the central and nodular zones lose neurogranin expression between approximately P4 and P6, whereas expression in the posterior zone persists until approximately P20. Neurogranin immunoreactivity will be a valuable tool in helping to clarify the relationships between early- and late-onset patterns.

Complementary stripes of phospholipase Cβ3 and Cβ4 expression by Purkinje cell subsets in the mouse cerebellum

Transverse boundaries divide the cerebellar cortex into four transverse zones, and within each zone the cortex is further subdivided into a symmetrical array of parasagittal stripes. Several molecules believed to mediate long-term depression at the parallel fiber-Purkinje cell synapse are known to be expressed in stripes. We have therefore explored the distributions of phospholipase Cbeta3 and phospholipase Cbeta4, key components in the transduction of type 1 metabotropic glutamate receptor-mediated responses. The data reveal that both phospholipase Cbeta isotypes are expressed strongly in the mouse cerebellum in subsets of Purkinje cells. The two distributions are distinct and largely nonoverlapping. The pattern of phospholipase Cbeta3 expression is unique, revealing stripes in three of the four transverse zones and a uniform distribution in the fourth. In contrast, phospholipase Cbeta4 appears to be confined largely to the Purkinje cells that are phospholipase Cbeta3-negative. PLCbeta3 is restricted to the zebrin II-immunopositive Purkinje cell subset. Not all zebrin II-immunoreactive Purkinje cells express PLCbeta3: in lobules IX and X it is restricted to that zebrin II-immunopositive subset that also expresses the small heat shock protein HSP25. PLCbeta4 expression is restricted to, and coextensive with, the zebrin II-immunonegative Purkinje cell subset. These nonoverlapping expression patterns suggest that long-term depression may be manifested differently between cerebellar modules.

Post-natal changes of cyclin-dependent kinase 5 activator expression in the developing rat cerebellum

cDNA of cyclin-dependent kinase 5 (Cdk5) was cloned based on its primary sequence homology to Cdc2 and Cdk2. Cdk5 requires the neuronal Cdk5 activators such as p35 or p39(nck5ai) (p39) for its activity. In this study, we examined post-natal changes in the p39 expression pattern during the development of the rat cerebellum. p39 began to express in somata and dendrites of Purkinje cells at post-natal day 3 (PD3). In particular, at PD12, parasagittal bands (stripes) with p39 immunoreactivity were weakly observed. At PD21, p39-immunoreactive stripes were developed when compared with the PD12 group. At this age stage, p39 immunoreactivity became weak in somata of Purkinje cells, not forming stripes. At PD28, a series of parasagittal bands were more distinct than those of the PD21 group, and p39 immunoreactivity disappeared in Purkinje cells, not forming p39 immunoreactive stripes. In the adults, p39 immunoreactivity in Purkinje cells was similar to that found in the PD28 group which showed that parasagittal bands were very narrow, and became progressively more slender. Therefore, we suggest that the post-natal changes of p39 expression in Purkinje cells in the cerebellum is an autonomous characteristic of Purkinje cells with a role of Cdk5 activators.

Compartmentation of the reeler cerebellum: segregation and overlap of spinocerebellar and secondary vestibulocerebellar fibers and their target cells

The cerebellum of the reeler mutant mouse has an abnormal organization; its single lobule is composed of a severely hypogranular cortex and a central cerebellar mass (CCM) consisting of Purkinje cell clusters intermixing with the cerebellar nuclei. As such the reeler represents an excellent model in which to examine the effect of the abnormal distribution of cerebellar cells on afferent-target relationships. To this effect we studied the organization of the spinocerebellar and secondary vestibulocerebellar afferent projections in homozygous reeler mice (rl/rl) using anterograde tracing techniques. Spinal cord injections resulted in labeled spinocerebellar mossy fiber rosettes in specific anterior and posterior regions of the cerebellar cortex. Some vestiges of parasagittal organization may be present in the anterior projection area. Within the CCM, labeled fibers appeared to terminate on distinct groups of Purkinje cells. Thus, the spinocerebellar mossy fibers seem to form both normal and heterologous synapses in the reeler cerebellum. Secondary vestibular injections resulted in both retrograde and anterograde labeling. Retrograde labeling was seen in clusters of Purkinje cells and cerebellar nuclear cells; anterograde labeling was distributed in the white matter and in specific regions of the anterior and posterior cortex of the cerebellum. The labeled spinocerebellar and secondary vestibulocerebellar afferents overlapped in the anterior region but in the posterior region the vestibulocerebellar termination area was ventral to the spinocerebellar area. An area devoid of labeled terminals was also observed ventral to the posterior secondary vestibulocerebellar termination field. Using calretinin immunostaining it was determined that this area contains unipolar brush cells, a cell type found primarily in the vestibulocerebellum of normal mice. Our data indicate that despite of the lack of known landmarks (fissures, lobules) the spinocerebellar and vestibulocerebellar afferent projections in the reeler cerebellum do not distribute randomly but have specific target regions, and the position of these regions, relative to each other, appears to be conserved. Two caveats to this were the finding of overlapping terminal fields of these afferents in the anterior region, and a posteroventral region that contains unipolar brush cells yet is devoid of secondary vestibulocerebellar afferents. The distribution of Purkinje cells and cerebellar nuclear cells is not random either; those that give rise to cerebellovestibular efferents form distinct groups within the central cerebellar mass.

Nogo-A expression in the intact and injured nervous system

The expression of Nogo-A mRNA and protein in the nervous system of adult rats and cultured neurons was studied by in situ hybridisation and immunohistochemistry. Nogo-A mRNA was expressed by many cells in unoperated animals, including spinal motor, DRG, and sympathetic neurons, retinal ganglion cells, and neocortical, hippocampal, and Purkinje neurons. Nogo-A protein was strongly expressed by presumptive oligodendrocytes, but not by NG2+glia and was abundant in motor, DRG, and sympathetic neurons, retinal ganglion cells, and many Purkinje cells, but was difficult to detect in dentate gyrus neurons and some neocortical neurons. Cultured fetal mouse neocortical neurons and adult rat DRG neurons strongly expressed Nogo-A in their perikarya, growth cones, and axonal varicosities. All axons in the intact sciatic nerve contained Nogo-A and many but not all regenerating axons were strongly Nogo-A immunopositive after sciatic nerve transection. Ectopic muscle fibres that developed among the regenerating axons were also Nogo-A immunopositive. Following injury to the spinal cord, Nogo-A mRNA was upregulated around the lesion and Nogo-A protein was strongly expressed in injured dorsal column fibres and their sprouts which entered the lesion site. Following optic nerve crush, Nogo-A accumulated in the proximal and distal stumps bordering the lesions.

Mediolateral compartmentalization of the cerebellum is determined on the "birth date" of Purkinje cells

The adult cerebellum is functionally compartmentalized into clusters along the mediolateral axis (M-L clusters), and a variety of molecular makers are expressed in specific subsets of M-L clusters. These M-L clusters appear to be the basic structure in which cerebellar functions are performed, but the mechanisms by which cerebellar mediolateral compartmentalization is established are still unclear. To address these questions, we examined the development of M-L clusters using replication-defective adenoviral vectors. The adenoviral vectors effectively introduced foreign genes into the neuronal progenitor cells of the cerebellum in a birth date-specific manner, allowing us to observe the native behavior of each cohort of birth date-related progenitor cells. When the adenoviral vectors were injected into the midbrain ventricle of mouse embryos on embryonic days 10.5 (E10.5), E11.5, and E12.5, the virally infected cerebellar progenitor cells developed into Purkinje cells. Notably, the Purkinje cells that shared the same birth date formed specific subsets of M-L clusters in the cerebellum. Each subset of M-L clusters displayed nested and, in part, mutually complementary patterns, and these patterns were unchanged from the late embryonic stage to adulthood, suggesting that Purkinje cell progenitors are fated to form specific subsets of M-L clusters after their birth between E10.5 and E12.5. This study represents the first such direct observation of Purkinje cell development. Moreover, we also show that there is a correlation between the M-L clusters established by the birth date-related Purkinje cells and the domains of engrailed-2, Wnt-7B, L7/pcp2, and EphA4 receptor tyrosine kinase expression.

Expression and possible role of neuronal calcium sensor-1 in the cerebellum

Neuronal calcium sensor-1 (NCS-1) is a member of EF-hand calcium-binding protein superfamily, which is considered to modulate synaptic transmission and plasticity. In this mini-review, we first summarize distribution of NCS-1 in the cerebellum. NCS-1 is mainly detected in postsynaptic sites, such as somata and dendrites of Purkinje cells, stellate/basket cells and granule cells. In addition, GABAergic inhibitory stellate/basket cell axon terminals also contain NCS-1. Secondly, we describe cerebellar compartmentation defined by NCS-1. The NCS-1 immunostaining displayed characteristic parasagittal-banding pattern in the Purkinje cell layer and molecular layer, whereas there were no apparent bands in the granule cell layer. The alternating positively and negatively NCS-1-labeled Purkinje cell clusters contributed to this cerebellar compartmentation. In contrast, stellate/basket cells were uniformly NCS-1-positive throughout the cerebellum. Interestingly, NCS-1 and zebrin II exhibited a similar parasagittal-banding pattern. But it is noteworthy that NCS-1-negative/zebrin II-positive Purkinje cell clusters were detected selectively in anterior lobule vermis and paraflocculus. These results suggest that NCS-1 defines a novel pattern of cerebellar cortical compartmentation. Lastly, we describe recent data suggesting some relationship between NCS-1 and cerebellar long-term depression-related molecules, and discuss the possible role of NCS-1 in the cerebellum.

Abnormal dysbindin expression in cerebellar mossy fiber synapses in the mdx mouse model of Duchenne muscular dystrophy

The dystrophin-associated protein complex (DPC), comprising sarcoglycans, dystroglycans, dystrobrevins, and syntrophins, is a component of synapses both in muscle and brain. Dysbindin is a novel component of the DPC, which binds to beta-dystrobrevin and may serve as an adaptor protein that links the DPC to an intracellular signaling cascade. Disruption of the DPC results in muscular dystrophy, and mutations in the human ortholog of dysbindin have been implicated in the pathogenesis of schizophrenia. In both cases, patients also present with neurological symptoms reminiscent of cerebellar problems. In the mouse cerebellum, dysbindin immunoreactivity is expressed at high levels in a subset of mossy fiber synaptic glomeruli in the granular layer. Lower levels of dysbindin immunoreactivity are also detected in Purkinje cell dendrites. In the cerebellar vermis, dysbindin-immunoreactive glomeruli are restricted to an array of parasagittal stripes that bears a consistent relationship to Purkinje cell parasagittal band boundaries as defined by the expression of the respiratory isoenzyme zebrin II/aldolase c. In a mouse model of Duchenne muscular dystrophy, the mdx mutant, in which dystrophin is not expressed, there is a dramatic increase in the number of dysbindin-immunoreactive glomeruli in the posterior cerebellar vermis. Moreover, the topography of the terminal fields is disrupted, replacing the stripes by a homogeneous distribution. Abnormal synaptic organization in the cerebellum may contribute to the neurological problems associated with muscular dystrophy and schizophrenia.

Antigenic compartmentation of the cat cerebellar cortex

Despite the apparent uniformity in cellular composition of the mammalian cerebellar cortex, a complex topography is revealed by several expression patterns. Zebrin II, a polypeptide antigen identified as aldolase C, is one such marker which, in several species of mammals, is restricted to a subset of Purkinje cells that are clustered together to form a symmetrical and reproducible array of zones and stripes. In rodents the cerebellar cortex is divided into four transverse zones--anterior, central, posterior, and nodular. Each transverse zone is further subdivided mediolaterally into an array of parasagittal stripes. The similar zone and stripe organization partitions the hemispheres. Based upon a novel whole mount immunohistochemical staining procedure, we have now identified homologous zones and stripes in the feline cerebellum. In the cat cerebellum the somata of most Purkinje cells express zebrin II but parasagittal stripes may still be delineated owing to the alternating high and low zebrin II expression levels in the dendritic arbors. As in rodents, the cat cerebellum consists of four transverse zones with each zone subdivided into a unique combination of zebrin II parasagittal stripes, suggesting that a common architecture underlies the organization of the mammalian cerebellum.

The cyclin-dependent kinase 5 activator, p39, is expressed in stripes in the mouse cerebellum

Cyclin-dependent kinase 5 (Cdk5) activity is required for CNS development. The Cdk5 activator, p35, is well characterized but its isoform, p39, has been less studied. Previously, p39 mRNA expression in rat brain was shown to peak at 3 weeks postnatal, and the level remains high in the adult cerebellum [Neurosci Res 28 (1997) 355]. However, p39 protein expression and specific localization in the cerebellum, where p39 mRNA level significantly exceeds that of p35, have not been examined. Here, we explored the specific cerebellar localization of the p39 protein in the developing and adult mice. Adult cerebellar Purkinje cell somata and dendritic arbors were strongly positive for p39 but only rare and barely detectable p39 was observed in Purkinje cell axons. Cdk5 also localized in Purkinje cell somata and dendrites of the adult cerebellum, but p35 localized only in Purkinje cell somata, further suggesting a functional difference between p35 and p39. During development, cerebellar p39 was first noted at P10. Primary cultures of a developing cerebellum also showed strong p39 immunoreactivity in Purkinje cell somata and dendrites, but weak p39 immunoreactivity in Purkinje cell axons. Starting from P10, p39 was observed in a subset of Purkinje cells that form parasagittal bands throughout the vermis and hemispheres. These bands were bilaterally symmetrical and continuous from one lobule to another. Conversely, Cdk5 and p35 showed a uniform staining pattern. The pattern of p39 closely resembled that of zebrin II/aldolase C, suggesting that p39 may play a role in the adult cerebellum rather than in pattern development. This premise is consistent with the normal pattern of zebrin II/aldolase C zones and stripes in mutant p39-/- mice. The alternating p39 parasagittal band pattern may reflect a role for p39 or Cdk5/p39 in the functional compartmentation of the cerebellum.

EphA4 is not required for Purkinje cell compartmentation

The Purkinje cells of both the adult and the developing cerebellar cortex are organized into parasagittal stripes or 'segments' expressing a variety of biochemical markers. We show that in the developing mouse cerebellar cortex, members of the Eph receptor gene family are expressed in mediolaterally alternating Purkinje cell segments. Since members of the Eph receptors family have been shown to play a role in hindbrain segmentation and boundary formation (Philos. Trans. R. Soc. Lond. B: Biol. Sci. 355 (2000) 993), we analyzed the effect of a null mutation of the EphA4 gene on Purkinje cell compartmentation. Using well characterized markers of Purkinje cell compartmentation in both the developing and the adult cerebellum, we observed no significant alteration in the banding pattern of these markers between the EphA4 knockout mice and their wild type controls. The ribboned pattern of migrating granule cells in the developing cerebellum also appears unaltered. The expression of other members of this gene family, including ephrin-B2, EphA2, and ephrin-A1, in a compartmentalized pattern within the Purkinje cell layer suggests a possible redundancy and/or a compensation of EphA4 function in the segmental patterning of cerebellar Purkinje cells.

Topological relationship between corticotropin-releasing factor-immunoreactive cerebellar afferents and tyrosine hydroxylase-immunoreactive Purkinje cells in a hereditary ataxic mutant, rolling mouse Nagoya

Using immunohistochemistry we examined the distribution of corticotropin-releasing factor-positive cerebellar afferents and the topological relationship between their projections and the distribution of tyrosine hydroxylase-positive Purkinje cells in an ataxic mutant, rolling mouse Nagoya. In the mutants, some climbing fibers were more intensely stained for corticotropin-releasing factor, but their zonal distribution remained the same as in non-ataxic littermates (control mice). These climbing fibers arose from the dorsal accessory nucleus, the ventral lamella of principal nucleus, the dorsomedial cell group, the subnucleus A, the beta subnucleus and the ventrolateral protrusion of the inferior olive, since perikarya in these olivary subdivisions were more intensely stained for corticotropin-releasing factor than in controls. Some mossy fiber rosettes in the vermal lobules, the simple lobule, the crus I of ansiform lobule, the copula pyramidis and the flocculus also exhibited corticotropin-releasing factor immunoreactivity and were more densely stained in the mutants than in controls. Double immunostaining for corticotropin-releasing factor and tyrosine hydroxylase in the mutant cerebellum revealed that the distribution of tyrosine hydroxylase-positive Purkinje cells corresponded to terminal fields of corticotropin-releasing factor-positive climbing fibers but not corticotropin-releasing factor-positive mossy fibers. This study indicated an increased corticotropin-releasing factor immunoreactivity in some climbing or mossy fibers in the cerebellum of rolling mouse Nagoya. We also found that the distribution of tyrosine hydroxylase-positive Purkinje cells corresponded to terminal fields of corticotropin-releasing factor-positive climbing fibers in the mutant cerebellum. As the transcription of the tyrosine hydroxylase gene is facilitated by Ca2+, abnormal tyrosine hydroxylase expression in the mutant Purkinje cells may indicate functional abnormality by alterations in intracellular Ca2+ concentrations. Therefore, we suggest that an increased level of corticotropin-releasing factor in a specific population of climbing fibers may alter the function of their target Purkinje cells.

Patterned cerebellar Purkinje cell death in a transgenic mouse model of Niemann Pick type A/B disease

Niemann Pick disease is a family of autosomal recessive disorders characterized by cholesterol accumulation. The most common type is Niemann Pick type A/B (NPA/B), resulting from deficient acid sphingomyelinase activity, which leads to sphingomyelin and cholesterol accumulation. The neuropathology of NPA/B includes widespread neuronal degeneration. An acid sphingomyelinase knockout mouse model of NPA/B (ASMKO) has been developed by the targeted deletion of the acid sphingomyelinase gene. When cerebellar morphology was examined in the ASMKO mouse at postnatal day 60 (P60), a dramatic pattern of longitudinal stripes was revealed in which roughly half the Purkinje cells had died, leaving a highly stereotyped, bilaterally symmetrical array of stripes. Antizebrin II immunocytochemistry revealed that the absent Purkinje cells corresponded exactly to the zebrin II-negative subset, leaving the zebrin II-positive subset apparently intact. By P120, some of the zebrin II-positive Purkinje cells had also been eliminated from the posterior vermis and hemispheres. By P180, all Purkinje cells had been lost from the anterior lobe. Finally at P240, almost all Purkinje cells had disappeared to leave a stereotyped distribution in lobules VI, IX-X and the flocculus and paraflocculus. The temporal pattern of Purkinje cell death demonstrates differential susceptibility of morphologically identical cells that appear to be linked to their molecular phenotypes.

Multiple zonal projections of the basilar pontine nuclei to the cerebellar cortex of the rat

This study revealed a sagittal zonal pattern of projections to the cerebellar cortex after hydraulic or iontophoretic injections of anterograde tracers (tritiated leucine, wheat germ agglutinin-horseradish peroxidase, or biotinylated dextrane amine) in the basilar pontine nuclei of Wistar rats. The zonal pattern of projection was observed only after injections of small size, whereas large injections labeled diffusely wide areas of the cerebellar cortex, masking the zonal projection because the fusion of contiguous stripes. Diverging projections to discrete sets of sagittal stripes in the two sides of the cerebellar cortex arose from single injections. The stripes of fiber terminals were sharply delimited on both sides by areas, interstripes, either virtually void of labeling or with a much lower density of labeling. Thus, the areas of the cerebellar cortex were parceled in sets of sagittal compartments, stripes and interstripes, by the pontine projections. Up to five compartments (three stripes and two interstripes) were observed in the paraflocculus, in the copula pyramidis, and in vermal lobule IX. Up to nine compartments (five stripes and four interstripes) were found in the crus I, the lobulus simplex, the paramedian lobule, and vermal lobules VI-VIII. Up to seven compartments (four stripes and three interstripes) were found in the crus II. Single injections into the basilar pontine nuclei usually labeled symmetric areas of the cerebellar cortex, which, in some cases, showed similar number of stripes. When this was not the case, the stripes were usually more numerous in the contralateral than in the ipsilateral side. All areas of the cerebellar cortex were projected upon, with zonation patterns from different regions of the basilar pontine nuclei. The projections of the basilar pontine nuclei to the cerebellar cortex were arranged according to a fixed pattern specific for each cortical area, independently of the number of stripes labeled within. The mean width of the stripes visualized in the single cortical areas of different rats was similar, despite the different size of the injections. The length of the stripes ranged widely in the various areas of different rats. The data collected in this study are consistent with the idea that all the mossy afferents to the cerebellar cortex are arranged with a zonal pattern.

Expression of heat-shock protein Hsp25 in mouse Purkinje cells during development reveals novel features of cerebellar compartmentation

The small heat shock protein Hsp25 is constitutively expressed in the adult mouse cerebellum by parasagittal stripes of Purkinje cells confined to the caudal central zone ( approximately lobules VI and VII), the nodular zone ( approximately ventral lobule IX and lobule X), and the paraflocculi/flocculi. During development several distinct phases in Hsp25 expression can be distinguished. Hsp25-immunopositive Purkinje cells are first seen at birth, when four clusters are visible in the vermis of lobules IV/V, and scattered Hsp25-immunoreactive Purkinje cells are seen in lobule VIII. By postnatal day 2/3, six narrow parasagittal stripes of Hsp25-immunopositive Purkinje cells are seen in the vermis of the anterior lobe. In the posterior lobules, most Purkinje cells in the vermis of lobules VIII and IX express Hsp25. This initial limited expression is followed by a phase of widespread expression (postnatal days 6-9) in which Hsp25 immunoreactivity is detected in virtually all Purkinje cells. This global cerebellar expression of Hsp25 then gradually disappears, first in the anterior zone and the hemispheres and subsequently in the posterior zone, to leave the restricted adult expression pattern. Western blotting analysis and immunoprecipitation with anti-Hsp25 suggest that all immunocytochemistry can be attributed the expression of Hsp25. Furthermore, visual deprivation had no effect on the development of Hsp25 expression in Purkinje cells, suggesting that visuomotor input is not responsible for the establishment of constitutive Hsp25 expression in the cerebellar cortex.

Pattern formation in the cerebellar cortex

The cerebellar cortex is subdivided rostrocaudally and mediolaterally into a reproducible array of zones and stripes. This makes the cerebellum a valuable model for studying pattern formation in the vertebrate central nervous system. The structure of the adult mouse cerebellar cortex and the series of embryological events that generate the topography are reviewed.Key words: zebrin, Hsp25, Purkinje cells.

Regional distribution and cell type-specific expression of the mouse F3 axonal glycoprotein: a developmental study

The expression of the mouse axonal adhesive glycoprotein F3 and of its mRNA was studied on sections of mouse cerebellar cortex, cerebral cortex, hippocampus, and olfactory bulb from postnatal days 0 (P0) to 30 (P30). In cerebellar cortex, a differential expression of F3 in granule versus Purkinje neurons was observed. F3 was highly expressed during migration of and initial axonal growth from cerebellar granule cells. The molecule was then downregulated on cell bodies and remained expressed, although at low levels, on their axonal extensions. On Purkinje cells, F3 was strongly expressed on cell bodies and processes at the beginning of the second postnatal week; by P16 it was restricted to neurites of Purkinje cells subpopulations. In the cerebral cortex, the molecule was highly expressed on migrating neurons at P0; by P16, it was found essentially within the neuropil with a diffuse pattern. In the hippocampal formation, where F3 was expressed on both pyramidal and granule neurons, a clear shift from the cell bodies to neurite extensions was observed on P3. In the olfactory pathway, F3 was expressed mainly on olfactory nerve fibers, mitral cells, and the synaptic glomeruli from P0 to P3, with a sharp decline from P11 to P16. As a whole, the data show that F3 protein expression is regulated at the regional, cellular, and subcellular levels and suggest that, in different regions, it can be proposed as a reliable neuronal differentiation marker.

Spatial correspondence between tactile projection patterns and the distribution of the antigenic Purkinje cell markers anti-zebrin I and anti-zebrin II in the cerebellar folium crus IIA of the rat

We have compared the band-like distribution of the Purkinje cell-specific polypeptides zebrin I and zebrin II with the spatial organization of tactile projections to crus IIa in the cerebellar hemisphere of the rat. Maps of tactile responses in the granular layer of the cerebellar hemispheres are fractured into discontinuous regions, termed "patches". High-density micromapping was used to identify specific patches and their boundaries within this fractured somatotopic map. In one series of experiments, medial and lateral boundaries of the large central ipsilateral upper lip-related patch were identified and labeled with either Fast Blue or India Ink. Following immunocytochemical processing, the band-like distribution of immunostained Purkinje cells (zebrin-positive bands) and the identified patch boundaries were digitized and reconstructed in three dimensions. Comparisons between these two features demonstrate a spatial correspondence between zebrin transitions and the boundaries of the electrophysiologically defined upper lip-related patch. In another series of experiments, we outlined the boundaries or centers of several smaller patches consistently located in the medial portion of the folium. Again, we found a correspondence between the distribution of granule cell layer tactile patches and the zebrin staining pattern. The correspondence between tactile projection patterns and molecular features demonstrated in the present study implies that there is a distinct and largely fixed spatial pattern of organization in the cerebellar hemispheres. We discuss possible causal connections and developmental determinates, as well as the physiological significance of the correspondence between the two features.

A patchy horizontal organization of the somatosensory activation of the rat cerebellum demonstrated by functional MRI

Blood oxygenation level dependent contrast (BOLD) functional MRI (fMRI) responses, in a 7-T magnet, were observed in the cerebellum of alpha-chloralose anaesthetized rats in response to innocuous electrical stimulation of a forepaw or hindpaw. The responses were imaged in both coronal and sagittal slices which allowed for a clear delineation and localization of the observed activations. We demonstrate the validity of our fMRI protocol by imaging the responses in somatosensory cortex to the same stimuli and by showing reproducibility of the cerebellar responses. Widespread bilateral activations were found with mainly a patchy and mediolateral band organization, more pronounced ipsilaterally. Possible parasagittal bands were observed only in contralateral lobule VI. There was no overlap between the cerebellar activations caused by forepaw and hindpaw stimuli. The overall horizontal organization of these responses was quite remarkable. For both stimulation paradigms most of the activation patches were positioned in either a rostral or caudal broad plane running anteroposteriorly through both anterior and posterior cerebellum. The rostral planes were completely separated, with the forepaw activation closer to the surface, while the caudal plane was common to both stimulation protocols. We relate our findings to the known projection patterns of spinocerebellar and cuneocerebellar mossy fibres, and to human fMRI studies.

Selective disruption of "late onset" sagittal banding patterns by ectopic expression of engrailed-2 in cerebellar Purkinje cells

To explore the role of Engrailed proteins in development of the cerebellum, Engrailed-2 (En-2) was ectopically expressed in cerebellar Purkinje cells from the late embryonic stage into adulthood. The fundamental organization of Purkinje cell sagittal zones as revealed by the "early onset" markers L7-beta-gal and cadherin-8 was found to be virtually identical to that in wild type. In contrast, "late onset" sagittal banding patterns revealed by Purkinje cell markers zebrin I, zebrin II, and 9-O-acetyl GD3 Ganglioside (P-Path), and the granule cell marker NADPH-diaphorase, were disrupted. In general, although some evidence of banding was still detectable, boundaries defined by the latter markers were poorly defined, and the patterns overall took on a diffuse appearance. In parallel with the changes in late onset markers, anterograde tracing of spinocerebellar axons revealed a general diffusion of the mossy fiber projection pattern in lobule VIII and the anterior lobe. These observations suggest that at least two separate mediolateral boundary systems exist in the cerebellum, and these are differentially affected by ectopic En-2 expression. Alternatively, one boundary system exists that remains primarily intact in the mutant, but recognition of this system by a set of late developmental events is perturbed.

Abnormal expression of tyrosine hydroxylase immunoreactivity in cerebellar cortex of ataxic mutant mice

Expression of tyrosine hydroxylase (TH) was examined immunohistochemically in the cerebellum of two ataxic mutants, Rolling mouse Nagoya (RMN) and dilute-lethal mice (DL). In littermate controls of both mutants, a few TH-positive Purkinje cells were distributed sparsely and their number was smaller than in the mutants at any ages examined. In RMN, TH-positive Purkinje cells were distributed in lobule IX and X, and were arranged into parasagittal bands at 2 weeks of age. TH-positive Purkinje cells increased in number and were widely distributed throughout the vermis at 3 weeks of age. In adult RMN, TH-positive Purkinje cells were found in all lobules of the cerebellum. Their parasagittal bands also became evident in the hemisphere. In DL, TH-positive Purkinje cells were mainly distributed in vermal lobules IX and X, and the flocculus at 3 weeks of age. They were also found as bands in lobules IX and X. The results suggest that abnormal expression of TH in Purkinje cells may not be specific to the allelic group. Since TH promoter is activated by Ca2+, TH expression in the mutant Purkinje cells may predict neuronal dysfunction caused by alterations in cellular Ca2+ currents.

Origin, course, and laterality of spinocerebellar axons in the North American opossum, Didelphis virginiana

Spinocerebellar axons have been studied extensively in placental mammals, but there have been no full reports on their origin, laterality, or spinal course in any marsupial. We have used the North American opossum (Didelphis virginiana) to obtain such information and to ask whether any spinocerebellar neurons innervate both the anterior and posterior lobes of the cerebellum through axonal collaterals. To identify spinal neurons that project to the cerebellum, we employed the retrograde transport of Fluoro-Gold (FG) from the anterior lobe, the main target of spinocerebellar axons. In some cases, cerebellar injections of FG were combined with hemisections of the rostral cervical or midthoracic spinal cord, so that laterality of spinocerebellar connections could be established. To determine whether single neurons project to both the anterior lobe and the posterior lobe, injections of Fast Blue (FB) into the anterior lobe were combined with injections of Diamidino yellow (DY) or rhodamine B dextran (RBD) into the posterior lobe, or vice versa. Following injections of FG into the anterior lobe, neurons were labeled throughout the length of the spinal cord, which differed in laminar distribution and laterality of their projections. Among other areas, neurons were labeled in the central cervical nucleus, the nucleus centrobasalis, Clarke's nucleus, the dorsal horn dorsal spinocerebellar tract area, the spinal border region, and Stilling's nucleus. When anterior lobe injections of FB were combined with injections of RBD or DY into the posterior lobe, or vice versa, some double-labeled neurons were present in all major spinocerebellar groups. Cerebellar injections of FG also retrogradely labeled spinocerebellar axons, allowing us to document their locations in the gray matter as well as within the periphery of the lateral and ventral funiculi at all spinal levels. A few spinocerebellar axons also were found in the dorsal funiculus (a dorsal column-spinocerebellar tract), which appeared to originate from neurons in the dorsal part of Clarke's nucleus from the ninth thoracic segment to the first lumbar segment. Our results indicate that spinocerebellar axons in the marsupial opossum are generally comparable in origin, course, and laterality to the same axons in the placental mammals studied to date.

Transient c-fos gene expression in cerebellar development and functional stimulation

This study examined the temporal appearance of c-fos expression in rat cerebella from birth to postnatal day 21 (P21) and following systemic kainic acid administration in adults. During development, Fos positive granule cells appeared first at P3 in caudal lobules and extended to all folia by P9. These reactive cells occurred in clusters throughout the granular layer and reached their highest reactivity by P15. In addition, Fos positive basket and stellate cells were seen in the molecular layer at this time. A steep decline in Fos protein labeling of the cerebellum began by P18 and was barely detectable in adulthood. In adult rats, systemic injection of kainic acid induced c-fos expression in granule cells and stellate/basket interneurons within 1 h of treatment. Fos reactive granule cells appeared in clusters with some forming distinct parasagittal bands in caudal folia. One day after unilateral cerebellar lesioning, a limited number of reactive cells were found on the lesion margins. A combination of lesioning and systemic kainic acid produced a strong, c-fos expression throughout the ipsilateral granular layer as well as in Purkinje cell nuclei. Contralateral to the lesion, the pattern of granule cell reactivity appeared the same but slightly stronger than those with kainate alone. We conclude that c-fos gene expression occurs transiently in granule cells during postnatal development and can be rapidly re-induced in the adult following systemic injection of glutamate agonists. The c-fos expression patterns suggest that subpopulations of granule cells are clustered and related to the parasagittal compartments of Purkinje cells.

Spatial organization of proprioception in the cat spinocerebellum. Purkinje cell responses to passive foot rotation

This study examines the spinocerebellar locations of Purkinje cells that responded to passive foot rotations at the ankle joint in anaesthetized cats. Using a novel approach for mapping the locations of recorded cells from several animals onto an unfolded two-dimensional representation of the cortex, we found that cells distributed throughout the anterior-posterior extent of the spinocerebellar cortex, except in the most medial parts corresponding to zones a and b, were responsive to ankle joint rotation. The cell distributions revealed a clustering according to their response amplitudes, which showed evidence for both parasagittal and transverse banding.

Novel receptor protein tyrosine phosphatase (RPTPrho) and acidic fibroblast growth factor (FGF-1) transcripts delineate a rostrocaudal boundary in the granule cell layer of the murine cerebellar cortex

We have identified a novel receptor-like protein tyrosine phosphatase (RPTPrho) transcript whose expression in the cerebellar cortex is restricted to the granule cell layer of lobules 1-6. Acidic fibroblast growth factor (FGF-1) mRNA follows a similar cerebellar expression pattern. Together, the two markers define a sharp boundary in lobule 6, slightly caudal to the primary fissure. Anterior and posterior compartments became discernible only during postnatal weeks two and six, for RPTPrho and FGF-1, respectively. A rostrocaudal boundary in lobule 6 of the murine cerebellar cortex has also been identified morphologically by the effects of the meander tail mutation. The position of the RPTPrho and FGF-1 boundary on the rostrocaudal axis of the cerebellar cortex was close to, but not coincident with, the caudal extent of the disorganized anterior lobe of meander tail and the rostral extent of Otx-2 expression. The restricted pattern of FGF-1 and RPTPrho implies that these molecules may have specific signaling roles in the tyrosine phosphorylation/dephosphorylation pathway in the anterior compartment of the adult cerebellar cortex.

Calcium-binding proteins in primate cerebellum

Single and double antigen localization procedures were used to study the distribution of the calcium-binding proteins calretinin, calbindin and parvalbumin in the cerebellum of the squirrel monkey (Saimiri sciureus). The immunostaining experiments have revealed that each of the three calcium-binding proteins occurred, either alone or in various combinations, in many neuronal types of the monkey cerebellum, including the Purkinje cells. Immunoreactivity for calbindin was detected in virtually all Purkinje cells, whereas immunoreactivity for calretinin and parvalbumin was encountered only in some subpopulations of Purkinje cells. In the vermal region, parvalbumin immunostaining appeared in the form of typical weak and strong alternating parasagittal bands. Calretinin immunoreactivity was found in virtually all neurons and fiber systems related to the granular layer, including the monodendritic cells, the granule cells and their parallel fibers, the Golgi and Lugaro cells and the mossy fibers. The Golgi cells also displayed calbindin and parvalbumin immunoreactivity. Parvalbumin was found to labeled both the climbing and mossy fibers, as well as the basket and stellate cells lying in the molecular layer. These results reveal that virtually all the different neuronal types in the primate cerebellum contain at least one of three calcium-binding proteins investigated in the present study. Furthermore, calretinin appears to be a particularly reliable molecular maker for all the neuronal elements associated with the granular layer in the primate cerebellum.

Pattern deformities and cell loss in Engrailed-2 mutant mice suggest two separate patterning events during cerebellar development

Null alleles of the mouse Engrailed-2 gene, a molecular homolog of the fly gene engrailed, have demonstrable effects on the anteroposterior (A/P) patterning of cerebellum as reflected in the disruption of the normal process of foliation of the cerebellar cortex and the alteration of transgene expression boundaries in the adult. Engrailed-2 also affects the transient mediolateral (M/L) pattern of En-1 and Wnt-7b expression seen in late embryogenesis. We have examined three markers of cerebellar compartmentation in En-2 mutant mice: the Zebrin II and Ppath monoclonal antibodies and the transgene L7lacZ. In En-2 mutants, the normal temporal pattern of expression is preserved for all three markers, although the size and spatial location of various bands differ from those of the wild type. Unlike the foliation abnormalities, the M/L pattern disturbances we have found occur in nearly all cerebellar regions. Cell counts reveal that all major cell types of the olivocerebellar circuit are reduced by 30-40%. We propose that these results are best explained by a model in which the Engrailed-2 gene is involved in the early specification of the cerebellar field including the number of progenitors. Because each of these progenitors gives rise to a clone of defined size, Engrailed-2 helps specify adult cell number. We further postulate that the configuration of the seven Zebrin bands as well as the shapes and locations of the cerebellar lobules are set up by a second patterning event that occurs after neurogenesis is complete.

Quantitative analysis of cuneocerebellar projections in rats: differential topography in the anterior and posterior lobes

The distribution of wheatgerm agglutinin-horseradish peroxidase-labelled mossy fibre terminals of internal and external cuneate projections to the cerebellar anterior and posterior lobes were quantitatively analysed in adult rats. Computer-based image analysis mapped the spatial distribution of labelled cuneocerebellar terminals in two-dimensional reconstructions of the unfolded cortex. Cuneocerebellar projections are mainly ipsilateral in their distribution. Cuneate projections to the anterior lobe vermis-medial paravermis terminate in well-circumscribed, irregularly-shaped patches. These terminal patches are aligned and form a longitudinally continuous, parasagittally oriented stripe in the lateral vermis-medial paravermis of lobules I-V. These terminal patches represent the topographically organized divergent projections of different parts of the internal and external cuneate nuclei. Cuneocerebellar projections to the lateral paravermis-hemisphere, particularly in the posterior part of lobule V, are organized as a transversely oriented band of terminals. Cuneocerebellar projections to the posterior lobe terminate mainly in three transversely oriented bands of terminals located at the junction between lobules. An anterior band of terminals was located in lobule VI anteriorly and was continuous with the band of terminals located in the posterolateral part of lobule V at the junction of these two lobules. Intermediate and posterior transversely oriented bands of terminals were located at the VII-VIII and VIII-IX junctions, respectively. Cuneocerebellar projections to these three bands largely appear to represent convergent projections from different parts of the cuneate nuclei. These findings are discussed in relation to similarly analysed and previously reported findings on the organization of lower thoracic-upper lumbar spinocerebellar projections and in the context of how cuneocerebellar somatosensory input may be differentially organized and processed in disparate areas of the cerebellar cortex.

Evidence of spinocerebellar mossy fiber segregation in the juvenile staggerer cerebellum

Developmental and experimental studies of climbing fiber and mossy fiber connectivity in the cerebellum have suggested that Purkinje cells are the critical organizing elements for connectivity patterns. This hypothesis is supported by evidence that spinocerebellar mossy fiber projections are abnormally diffuse in P25 sg/sg mutant mice in which the differentiation of a reduced number of sg/sg Purkinje cells is blocked due to a cell autonomous defect. However, mossy fiber distribution may be disrupted in sg/sg mutants not because of the Purkinje cell deficits, but because of the death of virtually all granule cells following the 4th postnatal week. To test this hypothesis, we have analyzed the distribution of wheat germ agglutinin-horseradish peroxidase (WGA-HRP)-labeled spinocerebellar mossy fiber terminals in sg/sg mutants at the end of the period of granule cell genesis (postnatal day [P] 12-P13) and before massive granule cell death (P16). Two percent WGA-HRP was injected into the lower thoracic/upper lumbar region of the spinal cord of eight homozygous sg/sg mutants (P12-P16) and five controls (+/sg and +/+). We have found that spinocerebellar mossy fibers segregate into distinct terminal fields in the anterior cerebellar lobules of P12 to P16 sg/sg mutants, although the medial-lateral distribution of spinocerebellar mossy fiber projections is different from controls. The results from this study and previous analysis of sg/sg mutants support the hypothesis that topographic cues are expressed in the early postnatal staggerer mutant, but mossy fiber terminals become disorganized or retract as granule cells die in the older staggerer mutant. J. Comp. Neurol. 378:354-362, 1997.

The compartmentalization of the cerebellum

The concept of developmental compartments originated in studies of Drosophila embryogenesis. This review examines the hypothesis that the modular structure of the vertebrate cerebellum is strongly analogous to this earlier scheme. The pattern of cerebellar development, the adult circuitry, a variety of molecular markers expressed in specific subdivisions, and the phenotypes of several neurological mutations all provide abundant evidence that the vertebrate cerebellum is organized into modules. We present the case that, as a group, these markers reveal distinct boundaries that partition the cerebellum into true developmental compartments. Although this reductionist viewpoint advances our understanding of cerebellar organization, the relationship between these compartments and the functional behavior of the cerebellum remains a mystery.

Comparison of projection neurons in the pontine nuclei and the nucleus reticularis tegmenti pontis of the rat

Dendritic features of identified projection neurons in two precerebellar nuclei, the pontine nuclei (PN) and the nucleus reticularis tegmenti pontis (NRTP) were established by using a combination of retrograde tracing (injection of fluorogold or rhodamine labelled latex micro-spheres into the cerebellum) with subsequent intracellular filling (lucifer yellow) in fixed slices of pontine brainstem. A multivariate analysis revealed that parameters selected to characterize the dendritic tree such as size of dendritic field, number of branching points, and length of terminal dendrites did not deviate significantly between different regions of the PN and the NRTP. On the other hand, projection neurons in ventral regions of the PN were characterized by an irregular coverage of their distal dendrites by appendages while those in the dorsal PN and the NRTP were virtually devoid of them. The NRTP, dorsal, and medial PN tended to display larger somata and more primary dendrites than ventral regions of the PN. These differences, however, do not allow the differentiation of projection neurons within the PN from those in the NRTP. They rather reflect a dorso-ventral gradient ignoring the border between the nuclei. Accordingly, a cluster analysis did not differentiate distinct types of projection neurons within the total sample. In both nuclei, multiple linear regression analysis revealed that the size of dendritic fields was strongly correlated with the length of terminal dendrites while it did not depend on other parameters of the dendritic field. Thus, larger dendritic fields seem not to be accompanied by a higher complexity but rather may be used to extend the reach of a projection neuron within the arrangement of afferent terminals. We suggest that these similarities within dendritic properties in PN and NRTP projection neurons reflect similar processing of afferent information in both precerebellar nuclei.

The Engrailed-2 homeobox gene and patterning of spinocerebellar mossy fiber afferents

The mouse Engrailed-2 gene, En-2, appears to be involved in cerebellar pattern formation. Homozygous null mutants for En-2 have abnormal foliation patterns in the posterior half of the cerebellum and there are changes in Purkinje and granule cell gene expression in some posterior folia, possibly reflecting changes in cell identity. We have examined the distribution of spinocerebellar mossy fiber terminals in homozygous En-2hd null mutants to determine if En-2 is involved in regulating the pattern of afferent connectivity in the cerebellum. Spinocerebellar mossy fiber terminals were labeled following WGA-HRP injections in the lumbar region of 5 homozygous En-2hd mutants and 4 heterozygous controls. The distribution of spinocerebellar mossy fiber terminals was consistently altered in lobules VIII and IX of the En-2hd mutants. The principal changes were a reduction in the number of mossy fiber terminal fields in the dorsal aspect of lobule VIII and the dorsal midline field in lobule IX was fused into a single compartment. The results suggest that the deletion of En-2 expression does not transform lobule identity, at least with respect to afferent fiber positional information cues. However, the changes in foliation and afferent connectivity in the En-2 mutant support a broad role for the En-2 gene in cerebellar patterning.

Ibogaine neurotoxicity: a re-evaluation

Ibogaine is claimed to be an effective treatment for opiate and stimulant addiction. O'Hearn and Molliver, however, showed that ibogaine causes degeneration of cerebellar Purkinje cells in rats. The present study re-examined cerebellar responses to the high doses of ibogaine used by O'Hearn and Molliver (100 mg/kg or 3 x 100 mg/kg) and sought to determine whether a lower dose (40 mg/kg), one effective in reducing morphine and cocaine self-administration, produced similar responses. Purkinje cell degeneration was evaluated with a Fink-Heimer II stain, and enhanced glial cell activity with an antibody to glial fibrillary acidic protein. Every rat treated with the high dose of ibogaine displayed clear evidence of Purkinje cell degeneration. The degeneration consistently occurred in the intermediate and lateral cerebellum, as well as the vermis. Purkinje cells in lobules 5 and 6 were particularly susceptible. Given the response properties of cells in these lobules, this finding suggests any long-term motor deficits produced by ibogaine-induced degeneration should preferentially affect the head and upper extremity. In marked contrast, rats given the smaller dose of ibogaine displayed no degeneration above the level seen in saline-treated animals. When combined with information on other compounds, these data suggest that the degenerative and "anti-addictive' properties of ibogaine reflect different actions of the drug.

Partial ablation of the neonatal external granular layer disrupts mossy fiber topography in the adult rat cerebellum

The spinocerebellar projection in the rat is compartmentalized in an array of parasagittal bands of mossy fiber terminals. These bands align reproducibly with bands of Purkinje cells that differentially express zebrin II. To investigate whether this alignment is obligatory, Purkinje cell and mossy fiber compartmentation has been compared in the rat cerebellum where the cytoarchitecture was contorted by neonatal administration of methylazoxymethanol. Methylazoxymethanol ablates many granule cell precursors, leaving a much reduced external granular layer, and adult rats that received a single methylazoxymethanol injection at birth showed varying degrees of abnormal cerebellar foliation. Zebrin II immunocytochemistry nevertheless revealed no fundamental abnormality in the Purkinje cell compartments. However, despite the normal Purkinje cell compartmentation being retained, the spinocerebellar mossy fiber-Purkinje cell topography is disrupted by methylazoxymethanol treatment. The normal precise array of parasagittal mossy fiber terminal fields becomes blurred across the lobule, and the normal clear banding is difficult to follow. These data suggest that, despite the early topography being dependent on the Purkinje cells, the granule cell-mossy fiber interactions also regulate the topography of the spinocerebellar projection.

White matter of the cerebellum of the chicken (Gallus domesticus): a quantitative light and electron microscopic analysis of myelinated fibers and fiber compartments

Low magnification light microscopic examination of the white matter in appropriately stained avian and mammalian cerebellum reveals a mediolateral succession in which areas of large, heavily myelinated fibers alternate with areas containing nearly exclusively small fibers. A large fiber accumulation (LFA) and its medially adjoining small fiber area (SFA) form a fiber compartment, which, with related parts of cortex and central nuclei, constitutes a so-called cerebellar module. The composition and the apparent mediolateral heterogeneity of cerebellar fiber compartments was quantified in the chicken by morphometrical analysis of myelinated fiber profiles in light (LM) and electron (EM) microscopic micrographs. In LM versus EM, approximately 37% of the myelinated fiber population is neglected. This deficit concerns profiles that are smaller than 1.2 micron2 (diameter < 1.2 microns). EM analysis is therefore considered a prerequisite and forms the main part of this study. The myelinated fiber population has a left-skewed log normal size distribution. Ninety-nine percent of the myelinated fibers fall within the range of 0.1 to 20 microns2 (diameter = 0.4-5.0 microns) and 90% are even smaller than 7 micron2 (diameter < 3.0 microns). Small fibers are abundant in both parts of the compartment. Statistical comparisons provide quantitative confirmation of the LM distinction of LFAs and SFAs. It appears, moreover, that, apart from typical LFAs and SFAs, transitional zones rather than sharp borders can be distinguished between the two. The medial border of the LFA appears to be more sharply defined than its lateral border. Distinct mediolateral fluctuations were found with respect to fiber density (166-243 fibers/1,000 microns2), mean profile area (2.4-4.0 microns2), and interspace (31-47%). These differences reflect the contrast between LFA (lower density, larger mean profile area) and SFA (higher density, smaller mean profile area). The interspace discriminates less well between LFA and SFA but is often smaller in the LFA and larger in the SFA. The presented quantitative characteristics of mediolateral heterogeneity in the cerebellar fiber layer can be used as reference for morphometric studies on the different fiber systems of the cerebellar white matter and the functional organization of the compartments.

Co-localization of tyrosine hydroxylase and zebrin II immunoreactivities in Purkinje cells of the mutant mice, tottering and tottering/leaner

The mutant mice tottering, leaner and the compound heterozygous tottering/leaner exhibit varying degrees of several abnormal neurological phenotypes including petit mal-like epilepsy, ataxia and an intermittent myoclonus-like movement disorder. Aberrant expression of tyrosine hydroxylase in cerebellar Purkinje cells of tottering, leaner and tottering/leaner mice has been observed previously [Austin M. C. et al. (1992) Molec. Brain Res. 15, 227-240; Hess E. J. and Wilson M. C. (1991) Neuron 6, 123-132]. In the present study, the distribution of tyrosine hydroxylase expression was compared with that of Zebrin II in Purkinje cells of adult homozygous tottering and compound heterozygous tottering/leaner mutant mice using single and double immunocytochemistry and double immunofluorescence. The pattern of Zebrin II expression in the cerebella of the mutant mice was identical to that described for normal mice [Hawkes R. et al. (1985) Brain Res. 333, 359-365; Hawkes R. and Leclerc N. (1987) J. comp. Neurol. 256, 29-41]. In addition, sections through tottering and tottering/leaner cerebella demonstrated an exact correspondence between the bands of tyrosine hydroxylase immunoreactivity and bands of Zebrin II immunoreactivity. Similarly, the compartments of the Purkinje cell layer which were negative for Zebrin II staining were also negative for tyrosine hydroxylase immunoreactivity. This study provides evidence that the cerebellar Purkinje cells of tottering and tottering/leaner mice were able to express a normal gene product, Zebrin II, in a normal spatial pattern and the same Purkinje cells can also express an aberrant gene product, tyrosine hydroxylase. This abnormal gene expression may indicate that at least some Purkinje cells in these mutant mice are not functioning normally. This possibility, taken together with the morphological changes observed in many mutant Purkinje cell axons, suggests that Purkinje cell function could be altered in tottering and tottering/leaner mice, thereby contributing to the neurological abnormalities exhibited by these mice. It is also possible that alteration in function of mutant Purkinje cells could correlate with the rostrocaudal zonation pattern described in this study.

A role for En-2 and other murine homologues of Drosophila segment polarity genes in regulating positional information in the developing cerebellum

To gain insight into the molecular genetic basis of cerebellar patterning, the expression patterns of many vertebrate homologues of Drosophila segment polarity genes were examined during normal and abnormal cerebellar development, including members of the En, Wnt, Pax, Gli and Dvl gene families. Five of these genes were found to show transient, spatially restricted patterns of expression. Strikingly, expression of En-2, En-1, Wnt-7B and Pax-2 defined eleven similar sagittal domains at 17.5 dpc, reminiscent of the transient sagittal domains of expression of Purkinje cell markers which have been implicated in cerebellar afferent patterning. Postnatally, transient anterior/posterior differences in expression were observed for En-2, En-1, Gli and Wnt-7B dividing the cerebellum into anterior and posterior regions. The expression patterns of these genes were altered in cerebella of En-2 homozygous mutant mice, which show a cerebellar foliation patterning defect. Strikingly, four of the Wnt-7B expression domains that are adjacent to the En-2 domains are lost in En-2 mutant embryonic cerebella. These studies provide the first evidence of a potential network of regulatory genes that establish spatial cues in the developing cerebellum by dividing it into a grid of positional information required for patterning foliation and afferents. Taken together with previous gene expression studies, our data suggests that eleven sagittal domains and at least two anterior/posterior compartments are the basic elements of spatial information in the cerebellum.

Chemical heterogeneity in adult rat cerebellar Purkinje cells as revealed by zebrin I and low-affinity nerve growth factor receptor immunocytochemical expression following injury

Cerebellar Purkinje cells in rat express low-affinity nerve growth factor receptor during development, but rarely in normal adult animals. However, after either mechanical injury or colchicine treatment during adulthood, these cells re-express low-affinity nerve growth factor receptor-immunoreactive protein. Two Purkinje cell subpopulations were defined in normal adult cerebellum by the presence or the absence of zebrin I antigen. Nevertheless, it remains an open question as to whether low-affinity nerve growth factor receptor-immunoreactive protein can be expressed by all damaged Purkinje cells, independent of their location and their staining with antibodies against intrinsic molecular markers that reveal Purkinje cell heterogeneity, such as zebrin I. In this study, a serial-section immunocytochemical mapping of the expression zebrin I and low-affinity nerve growth factor receptor, using specific monoclonal antibodies, we carried out in colchicine-treated rats. After mechanical damage of the cerebellar cortex, co-localization of these antigens at the cellular level was also analysed in thin adjacent sections, and by using a combined immunocytochemical staining method in individual sections. The findings revealed the existence of three sub-sets of Purkinje cells: (1) two complementary groups distinctly immunoreactive to one antibody, but not to the other and (2) a third group that contained double-labelled cells. In contrast, co-expression of both antigens was never observed following mechanical lesions. The seemingly independent response to mechanical injury of Purkinje cells located in different zebrin-defined compartments, indicates that particular subpopulations of Purkinje cells may respond differentially to traumatic injury.

5'-nucleotidase activity as a synaptic marker of parasagittal compartmentation in the mouse cerebellum

In the molecular layer of the mouse cerebellum, the histochemical activity of the adenosine-producing ectoenzyme 5'-nucleotidase discloses a parasagittal pattern of alternating enzyme-rich and enzyme-poor bands. In the rat, 5'-nucleotidase activity transiently labels cerebellar synapses during postnatal development and shifts later on towards an exclusive glial location in the molecular layer. We therefore asked whether different ultrastructural expression of 5'-nucleotidase would account for the light microscopic pattern seen in the adult mouse cerebellum. Using an enzyme cytochemical method, we localized 5'-nucleotidase activity on the glial cells and at the main types of asymmetrical synapses in the developing and mature cerebellum of the mouse. The percentage of labelled synapses increased until adulthood within the 5'-nucleotidase-positive bands. Here, the vast majority (86%) of the synapses were labelled against only 27% within the negative bands in the adult. Thus, 5'-nucleotidase appears as a marker of glia and of Purkinje cell synapses across cerebellar compartments. Changes in purinergic neuromodulation and/or cell adhesion mediated by 5'-nucleotidase across bands might participate in the functional differentiation of the cerebellar parasagittal subsets.