Intraparenchymal grafting of cerebellar cell suspensions to the deep cerebellar nuclei of pcd mutant mice, with particular emphasis on re-establishment of a Purkinje cell cortico-nuclear projection

Quantification of Solid Embryonic Cerebellar Graft Volume in a Degenerative Ataxia Model

Substitution of lost neurons by neurotransplantation would be a possible management of advanced degenerative cerebellar ataxias in which insufficient cerebellar reserve remains. In this study, we examined the volume and structure of solid embryonic cerebellar grafts in adult Lurcher mice, a model of olivocerebellar degeneration, and their healthy littermates. Grafts taken from enhanced green fluorescent protein (EGFP)-positive embryos were injected into the cerebellum of host mice. Two or six months later, the brains were examined histologically. The grafts were identified according to the EGFP fluorescence in frozen sections and their volumes were estimated using the Cavalieri principle. For gross histological evaluation, graft-containing slices were processed using Nissl and hematoxylin-eosin staining. Adjustment of the volume estimation approach suggested that it is reasonable to use all sections without sampling, but that calculation of values for up to 20% of lost section using linear interpolation does not constitute substantial error. Mean graft volume was smaller in Lurchers than in healthy mice when examined 6 months after the transplantation. We observed almost no signs of graft destruction. In some cases, compact grafts disorganized the structure of the host's cerebellar cortex. In Lurchers, the grafts had a limited contact with the host's cerebellum. Also, graft size was of greater variability in Lurchers than in healthy mice. The results are in compliance with our previous findings that Lurcher phenotype-associated factors have a negative effect on graft development. These factors can hypothetically include cerebellar morphology, local tissue milieu, or systemic factors such as immune system abnormalities.

Recent Advances in the Treatment of Cerebellar Disorders

Various etiopathologies affect the cerebellum, resulting in the development of cerebellar ataxias (CAs), a heterogeneous group of disorders characterized clinically by movement incoordination, affective dysregulation, and cognitive dysmetria. Recent progress in clinical and basic research has opened the door of the ‘‘era of therapy” of CAs. The therapeutic rationale of cerebellar diseases takes into account the capacity of the cerebellum to compensate for pathology and restoration, which is collectively termed cerebellar reserve. In general, treatments of CAs are classified into two categories: cause-cure treatments, aimed at arresting disease progression, and neuromodulation therapies, aimed at potentiating cerebellar reserve. Both forms of therapies should be introduced as soon as possible, at a time where cerebellar reserve is still preserved. Clinical studies have established evidence-based cause-cure treatments for metabolic and immune-mediated CAs. Elaborate protocols of rehabilitation and non-invasive cerebellar stimulation facilitate cerebellar reserve, leading to recovery in the case of controllable pathologies (metabolic and immune-mediated CAs) and delay of disease progression in the case of uncontrollable pathologies (degenerative CAs). Furthermore, recent advances in molecular biology have encouraged the development of new forms of therapies: the molecular targeting therapy, which manipulates impaired RNA or proteins, and the neurotransplantation therapy, which delays cell degeneration and facilitates compensatory functions. The present review focuses on the therapeutic rationales of these recently developed therapeutic modalities, highlighting the underlying pathogenesis.

Long-Term Development of Embryonic Cerebellar Grafts in Two Strains of Lurcher Mice

For many degenerative cerebellar diseases, currently, no effective treatment that would substantially restore cerebellar functions is available. Neurotransplantation could be a promising therapy for such cases. Nevertheless, there are still severe limitations for routine clinical use. The aim of the work was to assess volume and morphology and functional impact on motor skills of an embryonic cerebellar graft injected in the form of cell suspension in Lurcher mutant and wild-type mice of the B6CBA and C3H strains after a 6-month survival period. The grafts survived in the majority of the mice. In both B6CBA and C3H Lurcher mice, most of the grafts were strictly delimited with no tendency to invade the host cerebellum, while in wild-type mice, graft-derived Purkinje cells colonized the host's cerebellum. In C3H Lurcher mice, but not in B6CBA Lurchers, the grafts had smaller volume than in their wild-type counterparts. C3H wild-type mice had significantly larger grafts than B6CBA wild-type mice. No positive effect of the transplantation on performance in the rotarod test was observed. The findings suggest that the niche of the Lurcher mutant cerebellum has a negative impact on integration of grafted cells. This factor seems to be limiting for specific functional effects of the transplantation therapy in this mouse model of cerebellar degeneration.

Neurotransplantation therapy

Neurotransplantation may be a promising approach for therapy of cerebellar diseases characterized by a substantial loss of neurons. Neurotransplantation could rescue neurons from degeneration and maintain cerebellar reserve, facilitate cerebellar compensation, or help reconstruct damaged neural circuits by cell substitution. These mechanisms of action can be of varying importance according to the type of cerebellar disease. Neurotransplantation therapy in cerebellar ataxias is still at the stage of experimental studies. There is currently little knowledge regarding cerebellar patients. Nevertheless, data provided by experiments in animal models of cerebellar degeneration and both clinical studies and experiences in patients with other neurologic diseases enable us to suggest basic principles, expectations, limitations, and future directions of neurotransplantation therapy for cerebellar diseases.

An expandable embryonic stem cell-derived Purkinje neuron progenitor population that exhibits in vivo maturation in the adult mouse cerebellum

The directed differentiation of patient-derived induced pluripotent stem cells into cell-type specific neurons has inspired the development of therapeutic discovery for neurodegenerative diseases. Many forms of ataxia result from degeneration of cerebellar Purkinje cells, but thus far it has not been possible to efficiently generate Purkinje neuron (PN) progenitors from human or mouse pluripotent stem cells, let alone to develop a methodology for in vivo transplantation in the adult cerebellum. Here, we present a protocol to obtain an expandable population of cerebellar neuron progenitors from mouse embryonic stem cells. Our protocol is characterized by applying factors that promote proliferation of cerebellar progenitors. Cerebellar progenitors isolated in culture from cell aggregates contained a stable subpopulation of PN progenitors that could be expanded for up to 6 passages. When transplanted into the adult cerebellum of either wild-type mice or a strain lacking Purkinje cells (L7cre-ERCC1 knockout), GFP-labeled progenitors differentiated in vivo to establish a population of calbindin-positive cells in the molecular layer with dendritic trees typical of mature PNs. We conclude that this protocol may be useful for the generation and maturation of PNs, highlighting the potential for development of a regenerative medicine approach to the treatment of cerebellar neurodegenerative diseases.

Organization and Histochemical Phenotype of Human Fetal Cerebellar Cells following Transplantation into the Cerebellum of Nude Mice

Previous rodent studies have demonstrated the capacity of cerebellar transplants to organize into trilaminar cell layers typically observed in the normal cerebellum. In Purkinje Cell (PC)-deficient animals, PCs will migrate into the host and form synaptic connections. Recently, fetal cerebellar grafts transplanted into the Purkinje cell degeneration (pcd) mutant mouse were shown to result in an improvement of motor behaviors. These studies indicate the potential therapeutic use of neural transplantation in patients with cerebellar degeneration. In the present study, human fetal cerebellar tissue (8.5 wk postconception) was dissociated and transplanted into the normal cerebellum of nude mice. Six months following transplantation, histological analysis revealed donor cells in recipient mice. Immunostaining for the 28 kDa calcium-binding protein (calbindin) revealed the presence of donor PCs that were organized in discrete cellular layers within the transplant neuropil. In most cases the dendritic processes were oriented in a planar fashion perpendicular to the transplant cell layer. Human neurofilament immunostaining revealed bundles of donor fibers within the core of the transplant and/or at the periphery. These bundles were found to be calbindin positive (PC fibers). Three animals provided evidence of donor PC axon growth ventrally into host white matter, and in one case, this ventral migration reached the deep cerebellar nuclei. Most notable was the development of a pronounced folia-like organization by the implanted cell suspensions. Glial processes within the grafts were aligned perpendicular to the long axis of the transplant folia. These results demonstrate the capacity of human fetal cerebellar cell suspension to reorganize into cell layers typical of the normal cerebellum following transplantation into the rodent cerebellum, and develop an organotypic folia-like organization.

Amelioration of the Behavioral Phenotype in Genetically Ataxic Mice through Bilateral Intracerebellar Grafting of Fetal Purkinje Cells

We have previously applied neural grafting to “Purkinje cell degeneration” mutant mice (gene symbol pcd, mouse chromosome 13), a model of recessively inherited cerebello-olivary atrophy, to create appropriate interactions between wild-type and mutant cells in elucidating gene effects on the involved neuron populations and to address issues of the structural integration of donor Purkinje cells into the disrupted cerebellar loop. Behaviorally, pcd homozygotes manifest ataxic signs beginning at 3-4 wk of age. The functional effects of cerebellar transplants on motor performance have long remained an open question. The aim of the present study was to determine the recovery of motor responses in pcd mutants in a battery of behavioral tasks after bilateral transplantation of cerebellar cell suspensions (prepared from wild-type mice) into the parenchyma of the deep cerebellar nuclei of the hosts, according to a protocol that emphasizes the reconstruction of the missing inhibitory cortico-nuclear projection. With this approach, the denervated deep nuclei of the host receive a new Purkinje axonal innervation; further, most transplanted Purkinje cells end up occupying cortical localities anyway and display a correct dendritic tree orientation toward the pia. Motor coordination and fatigue resistance were assessed in a rotarod treadmill apparatus, a behavioral paradigm useful in studying various brain abiotrophies and treatments, including developmental perturbations of the cerebellar cytoarchitecture. Locomotor activity was quantified by the number of squares mice crossed as they moved about in an open-field matrix. Grafted pcd mice performed significantly better than sham-operated mutants in both of these tasks. Moreover, graft-recipient mice were able to sustain their abdomen above the floor on their limbs during movement, contrasting to the typical lowered, widened stance of sham-operated pcd mutants. These findings clearly demonstrate that bilateral transplants of fetal Purkinje cells have functional effects on motor performance in the pcd model of hereditary cerebellar ataxia.

Experimental neurotransplantation treatment for hereditary cerebellar ataxias

Hereditary cerebellar degenerations are a heterogeneous group of diseases often having a detrimental impact on patients’ quality of life. Unfortunately, no sufficiently effective causal therapy is available for human patients at present. There are several therapies that have been shown to affect the pathogenetic process and thereby to delay the progress of the disease in mouse models of cerebellar ataxias. The second experimental therapeutic approach for hereditary cerebellar ataxias is neurotransplantation. Grafted cells might provide an effect via delivery of a scarce neurotransmitter, substitution of lost cells if functionally integrated and rescue or trophic support of degenerating cells. The results of cerebellar transplantation research over the past 30 years are reviewed here and potential benefits and limitations of neurotransplantation therapy are discussed.

From mice to men: lessons from mutant ataxic mice

Ataxic mutant mice can be used to represent models of cerebellar degenerative disorders. They serve for investigation of cerebellar function, pathogenesis of degenerative processes as well as of therapeutic approaches. Lurcher, Hot-foot, Purkinje cell degeneration, Nervous, Staggerer, Weaver, Reeler, and Scrambler mouse models and mouse models of SCA1, SCA2, SCA3, SCA6, SCA7, SCA23, DRPLA, Niemann-Pick disease and Friedreich ataxia are reviewed with special regard to cerebellar pathology, pathogenesis, functional changes and possible therapeutic influences, if any. Finally, benefits and limitations of mouse models are discussed.

Morphological analysis of embryonic cerebellar grafts in SCA2 mice

SCA2 transgenic mice are thought to be a useful model of human spinocerebellar ataxia type 2. There is no effective therapy for cerebellar degenerative disorders, therefore neurotransplantation could offer hope. The aim of this work was to assess the survival and morphology of embryonic cerebellar grafts transplanted into the cerebellum of adult SCA2 mice. Four month-old homozygous SCA2 and negative control mice were treated with bilateral intracerebellar injections of an enhanced green fluorescent protein-positive embryonic cerebellar cell suspension. Graft survival and morphology were examined three months later. Graft-derived Purkinje cells and the presence of astrocytes in the graft were detected immunohistochemically. Nissl and hematoxylin-eosin techniques were used to visualize the histological structure of the graft and surrounding host tissue. Grafts survived in all experimental mice; no differences in graft structure, between SCA2 homozygous and negative mice, were found. The grafts contained numerous Purkinje cells but long distance graft-to-host axonal connections to the deep cerebellar nuclei were rarely seen. Relatively few astrocytes were found in the center of the graft. No signs of inflammation or tissue destruction were seen in the area around the grafts. Despite good graft survival and the presence of graft-derived Purkinje cells, the structure of the graft did not seem to promise any significant specific functional effects. We have shown that the graft is available for long-term experiments. Nevertheless, it would be beneficial to search for ways of enhancement of connections between the graft and host.

Concise review: stem cells for the treatment of cerebellar-related disorders

Embryonic neural transplants have become clinically relevant over the past 25 years for their possible application in the treatment of cerebellum-related neurodegenerative diseases. While highlighting the important role that fetal neural progenitors have in meeting these challenges, we define rationales for all types of cell therapy involving adult stem cells as well as human embryonic stem cells (hESC) and human induced pluripotent stem (iPS) cells. The recent advances in the field of hESC and iPS cells, including their capacity for differentiation toward regional specific neural lineages, could open a new era of transplantation in cell-based therapy for cerebellar ataxias.

Molecular/genetic manipulation of extrinsic axon guidance factors for CNS repair and regeneration

During development, guidance molecules play a key role in the formation of complex circuits required for neural functions. With the cessation of development, this exuberant growth process slows and stabilizes, and inhibitory molecules expressed by glia prevent initial attempts for axonal regeneration. In this review, we discuss the expression patterns and relative contribution of several guidance molecules on the regenerative process. Injury to the immature CNS or species capable of regenerating exhibit a complete or partial recapitulation of their developmental guidance patterns, whereas similar injuries to adult mammals results in altered expression that acts to further hinder regeneration. Manipulations of guidance molecules after injury have been used to control detrimental effects of axon sprouting and target regenerating axons within the spinal cord.

Neuronal replacement and integration in the rewiring of cerebellar circuits

Repair of CNS injury or degeneration by cell replacement may lead to significant functional recovery only through faithful reconstruction of the original anatomical architecture. This is particularly relevant for point-to-point systems, where precisely patterned connections have to be re-established to regain adaptive function. Despite the major interest recently drawn on cell therapies, little is known about the mechanisms and the potentialities for specific integration of new neurons in the mature CNS. Major findings and concepts about this issue will be reviewed here, with special focus on work dealing with the Purkinje cell transplantation in the rodent cerebellum. These studies show that the adult CNS may provide some efficient information to direct cell engraftment and process outgrowth. On their side, immature cells may be able to induce adaptive changes in their adult partners to facilitate their incorporation in the recipient network. Despite the rather high degree of specific integration achieved in several different CNS regions, these processes are usually defective and long-distance connections are not rewired. Thus, although some potentialities for cell replacement exist in the mature CNS, full incorporation of new neurons in adult circuits is rarely observed. Indeed, intrinsic mechanisms for growth control as well as injury-induced changes in the properties and architecture of the nervous tissue contribute to hamper repair processes. As a consequence, crucial to obtain successful cell replacement and integration in the mature CNS is a deep understanding of the basic biological mechanisms that regulate the interactions between newly added elements and the recipient environment.

Selective rather than inductive mechanisms favour specific replacement of Purkinje cells by embryonic cerebellar cells transplanted to the cerebellum of adult Purkinje cell degeneration (pcd) mutant mice

Cell replacement after neuronal degeneration in the adult CNS depends on the availability of specific cues to direct specification, differentiation and integration of newly born neurons into mature circuits. Following recent reports indicating that neurogenic signals may be reactivated in the adult injured CNS, here we asked whether such signals are expressed in the cerebellum after Purkinje cell degeneration. Thus, we compared the fate of embryonic cerebellar cells transplanted to the cerebella of adult wild-type and Purkinje cell degeneration (pcd) mutant mice. Donor cells were dissected from beta-actin-enhanced green fluorescent protein (EGFP) transgenic mice and transplanted as a single cell suspension. In both hosts, grafted cells generated all major cerebellar phenotypes, with a precise localization in the recipient cortex or white matter. Nevertheless, the phenotypic distributions showed striking quantitative differences. Most notably, in the pcd cerebellum there was a higher amount of Purkinje cells, while other phenotypes were less frequent. Analysis of cell proliferation by 5-bromo-2'-deoxyuridine (BrDU) incorporation revealed that in both hosts mitotic activity was strongly reduced shortly after transplantation, and virtually all donor Purkinje cells were actually generated before grafting. Together, these results indicate that some compensatory mechanisms operate in the pcd environment. However, the very low mitotic rate of transplanted cells suggests that the adult cerebellum, either wild-type or mutant, does not provide instructive neurogenic cues to direct the specification of uncommitted progenitors. Rather, specific replacement in mutant hosts is achieved through selective mechanisms that favour the survival and integration of donor Purkinje cells at the expense of other phenotypes.

Cerebellar allografts survive and transiently alleviate ataxia in a transgenic model of spinocerebellar ataxia type-1

Spinocerebellar ataxia type 1 (SCA-1) is one of several neurodegenerative diseases, including Huntington's disease, spinobulbar muscular atrophy, dentatorubral-pallidoluysian atrophy, and SCA-2, SCA-3, SCA-6, and SCA-7, each caused by an expanded number of CAG repeats in the coding region of their respective genes. The mechanism by which the resulting proteins are pathogenic is unknown. Clinical trials of neural transplants in Huntington's disease patients are under way. While initial reports are encouraging, definitive evidence of graft survival in patients despite the ongoing disease process is not possible with current imaging techniques. Transplants in primates have shown long-term survival of striatal grafts and recovery of function, but have used lesioning to model Huntington's phenotypically. Studies of striatal grafts in a transgenic mouse model of Huntington's have not yet shown a behavioral benefit. We describe a behavioral benefit of cerebellar grafts in a transgenic model of SCA-1 in which the ataxic phenotype results from expression of an expanded ataxin-1 protein. Mice were transplanted at an age when their ataxic phenotype is just becoming evident. Compared with sham-operated littermates, grafted mice showed better performance on multiple behavioral tests of cerebellar function. Differences persisted for 10 to 12 weeks posttransplant, after which there was a progressive decline in motor performance. At 20 weeks postsurgery, donor Purkinje cell survival was evident in 9 of 12 graft recipients. These results indicate that transplants can have behavioral benefits and grafts can survive long-term despite the ongoing pathological process in a brain actively expressing an expanded polyglutamine protein.

Mature astrocytes transform into transitional radial glia within adult mouse neocortex that supports directed migration of transplanted immature neurons

Neuronal migration is an essential step in normal mammalian neocortical development, and the expression of defined cellular and molecular signals within the developing cortical microenvironment is likely crucial to this process. Therapy via transplanted or manipulated endogenous precursors for diseases which involve neuronal loss may depend critically on whether newly incorporated cells can actively migrate to repopulate areas of neuronal loss within the adult brain. Previous studies demonstrated that embryonic neurons and multipotent precursors transplanted into the neocortex of adult mice undergoing targeted apoptosis of pyramidal neurons migrate long distances into neuron-deficient regions, undergo directed differentiation, accept afferent synaptic input, and make appropriate long-distance projections. The experiments presented here: (1) use time-lapse digital confocal imaging of neuronal migration in living slice cultures to assess cellular mechanisms utilized by immature neurons during such long distance migration, and (2) identify changes within the host cortical astroglial population that may contribute to this migration. Prelabeled embryonic day 17 mouse neocortical neurons were transplanted into adult mouse primary somatosensory cortex undergoing targeted apoptotic degeneration of callosal projection neurons. Four to 7 days following transplantation, living slice cultures containing the region of transplanted cells were prepared and observed. Sequential time-lapse images were recorded using a video-based digital confocal microscope. Transplanted cells displayed bipolar morphologies characteristic of migrating neuroblasts and moved in a saltatory manner with mean rates of up to 14 microm/h. To investigate whether a permissive glial phenotype may provide a potential substrate for this directed form of neuronal migration, slice cultures were immunostained with the RC2 monoclonal antibody, which identifies radial glia that act as a substrate for neuronal migration during corticogenesis. RC2 does not label mature stellate astrocytes, which express glial fibrillary acidic protein (GFAP). RC2 expression was observed in glial cells closely apposed to migrating donor neurons within the slice cultures. The timing and specificity of RC2 expression was examined immunocytochemically at various times following transplantation. RC2 immunostaining within regions of neuronal degeneration was transient, with peak staining between 3 and 7 days following transplantation. Strongly RC2-immunoreactive cells that did not express GFAP were found within these regions, but not in distant cortical regions or within control brains. RC2-positive cells were identified in recipient transgenic mice which express beta-galactosidase under a glial specific promoter. Coexpression of RC2 and beta-galactosidase identified these cells as host astroglia. These results demonstrate that adult cortical astrocytes retain the capacity to reexpress an earlier developmental phenotype that may partially underlie the observed active migration of transplanted neurons and neural precursors. Further understanding of these processes could allow directed migration of transplanted or endogenous precursors toward therapeutic cellular repopulation and complex circuit reconstruction in neocortex and other CNS regions.

Transplanted neurons alter the course of neurodegenerative disease in Lurcher mutant mice

Embryonic cerebellar, neocortical, and striatal tissues derived from NSE-LacZ transgenic mice were transplanted into the right cerebellar hemisphere of 8- to 10-day-old Lurcher or wild-type mice. Host mice survived for 30-90 days and the transplanted tissue was examined by light microscopy using Nissl staining, X-gal histochemistry, and immunohistochemistry for calcium binding protein and glutamic acid decarboxylase. Transplantation of cerebellar tissue, but not neocortical or striatal progenitors, resulted in robust infiltration of the lurcher mutant host cerebellar cortex by transgenic Purkinje neurons. Deep to the infiltrated molecular layer, the host granular layer was thicker and denser than the mutant granular layer, but transgenic cells did not contribute to the spared granular layer. The host inferior olivary complex consistently exhibited a noticeable bilateral asymmetry in Nissl-stained sections. A quantitative analysis of the olivary complex was performed in 10 90-day-old host mice. The results indicate that the left inferior olivary complex of 90-day-old host mice contained more neurons than the right inferior olive of the host mice and contained more neurons than was observed in 90-day-old Lurcher control mice. Analysis by olivary subdivision indicates that increased neuron numbers were present in all subdivisions of the host left inferior olive. These studies confirm the specific attractive effect of the mutant cerebellar cortex on transplanted Purkinje neuron progenitors and indicate that neural transplants may survive the neurodegenerative period to interact with developing host neural systems. The unilateral rescue of Lurcher inferior olivary neurons in cerebellar transplant hosts indicates that transplanted neurons may interact with diseased host neural circuits to reduce transneuronal degeneration in the course of a neurodegenerative disease.

Purkinje cell transplants in Shaker mutant rats with hereditary Purkinje cell degeneration and ataxia

Shaker mutant rats are characterized by the adult-onset degeneration of cerebellar anterior lobe Purkinje cells and temporally correlated development of ataxia and tremor. Normal E-13 Purkinje cells were transplanted into the anterior cerebellum in adult shaker mutant rats to study donor/host interactions in an animal with adult-onset heredodegeneration. Donor Purkinje cells from extraparenchymal transplant sites migrated radially into the host molecular layer and differentiated. Donor Purkinje cell dendrites expanded to fill the host molecular layer, spinous processes were apparent, and axonal projections into the host gray and white matter were observed. Donor Purkinje cells remaining in the extraparenchymal transplant sites differentiated if they were located relatively close to the host cerebellum. Donor Purkinje cells located intraparenchymally in the host white matter or granule cell layer survived, but were stunted in their development. The orthogonal movement of donor Purkinje cells away from transplant sites in the host cerebellum was spatially restricted. The findings from this study indicate that host cerebellar cortex with adult-onset heredodegeneration of Purkinje cells supports the survival and differentiation of transplanted normal embryonic Purkinje cells.

Cerebellar Grafts Partially Reverse Amino Acid Receptor Changes Observed in the Cerebellum of Mice with Hereditary Ataxia: Quantitative Autoradiographic Studies

We used quantitative autoradiography of [3H]CNQX (200 nM), [3H]muscimol (13 nM), and [3H]flunitrazepam (10 nM) binding to study the distribution of non-NMDA and GABAA receptors in the cerebellum of pcd mutant mice with unilateral cerebellar grafts. Nonspecific binding was determined by incubation with 1 mM Glu, 200 μM GABA, or 1 μM clonazepam, respectively. Saturation parameters were defined in wild-type and mutant cerebella. In mutants, non-NMDA receptors were reduced by 38% in the molecular layer and by 47% in the granule cell layer. The reduction of non-NMDA receptors in the pcd cerebellar cortex supports their localization on Purkinje cells. [3H] CNQX binding sites were visualized at higher density in grafts that had migrated to the cerebellar cortex of the hosts (4.1 and 11.0 pmol/mg protein, respectively, at 23 and 37 days after grafting) than in grafts arrested intraparen-chymally (2.6 and 6.2 pmol/mg protein, respectively, at 23 and 37 days after grafting). The pattern of expression of non-NMDA receptors in cortical vs. parenchymal grafts suggests a possible regulation of their levels by transacting elements from host parallel fibers. GABAA binding levels in the grafts for both ligands used were similar to normal molecular layer. Binding was increased in the deep cerebellar nuclei of pcd mutants: the increase in [3H]muscimol binding over normal was 215% and the increase in [3H]flunitrazepam binding was 89%. Such increases in the pcd deep cerebellar nuclei may reflect a denervation-induced supersensitivity subsequent to the loss of Purkinje axon terminal innervation. In the deep nuclei of pcd mutants with unilateral cerebellar grafts, [3H]muscimol binding was 31% lower in the grafted side than in the contralateral nongrafted side at 37 days after transplantation; [3H]fluni-trazepam binding was also lower in the grafted side by 15% compared to the nongrafted side. Such changes in GABAA receptors suggest a significant, albeit partial, normalizing trend of cerebellar grafts on the state of postsynaptic supersensitive receptors in the host cerebellar nuclei.

Amelioration of the behavioral phenotype in genetically ataxic mice through bilateral intracerebellar grafting of fetal Purkinje cells

We have previously applied neural grafting to "Purkinje cell degeneration" mutant mice (gene symbol pcd, mouse chromosome 13), a model of recessively inherited cerebello-olivary atrophy, to create appropriate interactions between wild-type and mutant cells in elucidating gene effects on the involved neuron populations and to address issues of the structural integration of donor Purkinje cells into the disrupted cerebellar loop. Behaviorally, pcd homozygotes manifest ataxic signs beginning at 3-4 wk of age. The functional effects of cerebellar transplants on motor performance have long remained an open question. The aim of the present study was to determine the recovery of motor responses in pcd mutants in a battery of behavioral tasks after bilateral transplantation of cerebellar cell suspensions (prepared from wild-type mice) into the parenchyma of the deep cerebellar nuclei of the hosts, according to a protocol that emphasizes the reconstruction of the missing inhibitory cortico-nuclear projection. With this approach, the denervated deep nuclei of the host receive a new Purkinje axonal innervation; further, most transplanted Purkinje cells end up occupying cortical localities anyway and display a correct dendritic tree orientation toward the pia. Motor coordination and fatigue resistance were assessed in a rotarod treadmill apparatus, a behavioral paradigm useful in studying various brain abiotrophies and treatments, including developmental perturbations of the cerebellar cytoarchitecture. Locomotor activity was quantified by the number of squares mice crossed as they moved about in an open-field matrix. Grafted pcd mice performed significantly better than sham-operated mutants in both of these tasks. Moreover, graft-recipient mice were able to sustain their abdomen above the floor on their limbs during movement, contrasting to the typical lowered, widened stance of sham-operated pcd mutants. These findings clearly demonstrate that bilateral transplants of fetal Purkinje cells have functional effects on motor performance in the pcd model of hereditary cerebellar ataxia.

The cerebellar model of neural grafting: structural integration and functional recovery

A synopsis is presented of the recent history of cerebellar tissue transplantation over the past 25 years. The properties of growth and differentiation of cerebellar grafts placed intraocularly or intracranially are reviewed, as well as the interaction of heterotopic and orthotopic grafts with the host brain. Particular emphasis is placed on the use of ataxic mouse mutants as recipients of donor cerebellar tissue for the correction of their structural deficits and the functional recovery of behavioural responses.

Grafted cerebellar cells in a mouse model of hereditary ataxia express IGF-I system genes and partially restore behavioral function

Fetal grafts of normal cerebellar tissue were implanted into the cerebellum of Purkinje cell degeneration mutant mice (pcd/pcd), a model of adult-onset recessively inherited cerebello-olivary atrophy, in an attempt at correcting their cellular and motor impairment. Donor cerebellar cells engrafted in the appropriate sites, as evidenced by the pattern of expression of insulin-like growth factor-I (IGF-I) system genes. Bilateral cerebellar grafts led to an improvement of motor behaviors in balance rod tests and in the open field, providing evidence for functional integration into the atrophic mouse cerebellum and underscoring the potential of neural transplantation for counteracting the human cerebellar ataxias.

Spatial and temporal pattern of Purkinje cell degeneration in shaker mutant rats with hereditary cerebellar ataxia

Temporal-spatial patterns of surviving Purkinje cells were studied quantitatively in a rat mutant (shaker) with differential hereditary cerebellar ataxia and Purkinje cell degeneration. Shaker rat mutants are characterized behaviorally as mild if they are ataxic or as strong if they have ataxia and tremor. Purkinje cells degenerate in both mild and strong shaker mutants, but the temporal and spatial patterns of cell death are strikingly different. In mild shaker mutants, Purkinje cell death is temporally restricted, with 31-46% of the Purkinje cells in lobules I-IX dying by 3 months of age. Very few Purkinje cells degenerate after this age. Purkinje cell death is spatially random. In lobules I-IX, every second, third, or fourth Purkinje cell degenerates. Purkinje cells in lobule X do not degenerate. In strong shaker mutants, Purkinje cell degeneration is temporally protracted and spatially restricted. By 3 months of age, most Purkinje cells in lobules I-VIa, -b, and -d have degenerated. Numerous Purkinje cells in the paravermis of lobules VIIb-VIII have also degenerated. Surviving Purkinje cells in the vermis and lateral hemisphere of lobules VIIb-VIII are aligned in parasagittally oriented stripes or transversely oriented bands. Purkinje cells continue to degenerate in localized areas of the posterior lobe such that, by 18 months of age, surviving Purkinje cells are limited primarily to lobules VIc, VIIa, IXd, and X. Quantitative analysis indicates that none of the Purkinje cells in these lobules degenerate.

Migration of purified embryonic motoneurons grafted into adult mouse CNS

Embryonic motoneurons were fluorescently-labelled with carbocyanine (diI) by means of retrograde transport and then grafted into the adult mouse spinal cord (L2) and brain (striatum) for 2-10 weeks. The motoneurons were grafted either following purification on the fluorescence-activated cell sorter or in the presence of embryonic glial cells and interneurons from the spinal cord. In both conditions of grafting, motoneurons were found to survive and develop in both grey and white matter and were found to migrate long distances in both regions of the central nervous system. Migration of neurons after grafting remains a controversial issue, therefore we have discussed the work of other groups that have described the same phenomenon.

Serotonin fiber innervation of cerebellar cell suspensions intraparenchymally grafted to the cerebellum of pcd mutant mice

One aspect of integration of implanted neurons into the neuronal circuitry of a defective host brain is the re-establishment of a host-to-graft afferent innervation. We addressed this issue by using the adult cerebellum of 'Purkinje cell degeneration' (pcd) mutant mice, which lack virtually all Purkinje cells after postnatal day (P) 45. Purkinje cells constitute one of the cerebellar cell types being innervated by axons of raphé serotonin (5-HT) neurons. In normal mice, 5-HT-immunoreactive fibers are distributed to all cerebellar folia. Following Purkinje cell loss in pcd mice, cerebellar 5-HT-immunoreactive fibers persist. Cerebellar cell suspensions were prepared from embryonic day (E) 11-13 normal mouse embryos and were intraparenchymally grafted into the cerebellum of pcd mutants either directly or after pre-treatment with 5,7-dihydroxytryptamine (5,7-DHT) to selectively remove 5-HT cells of donor origin. The state of Purkinje cells and 5-HT axons was monitored in alternate sections by 28-kDa Ca(2+)-binding protein (CaBP) and 5-HT immunocytochemistry, respectively. Serotonin-immunoreactive axons were seen in the grafts from 5 to 32 days after transplantation. In some of the grafts which had not been pre-treated with 5,7-DHT, a small number of 5-HT-immunoreactive cell bodies was found, indicating that part of the 5-HT fiber innervation of the graft could actually derive from donor cells.(ABSTRACT TRUNCATED AT 250 WORDS)