Long-distance axonal regeneration in the transected adult rat spinal cord is promoted by olfactory ensheathing glia transplants

The lack of axonal regeneration in the injured adult mammalian spinal cord leads to permanent functional impairment. To induce axonal regeneration in the transected adult rat spinal cord, we have used the axonal growth-promoting properties of adult olfactory bulb ensheathing glia (EG). Schwann cell (SC)-filled guidance channels were grafted to bridge both cord stumps, and suspensions of pure (98%) Hoechst-labeled EG were stereotaxically injected into the midline of both stumps, 1 mm from the edges of the channel. In EG-transplanted animals, numerous neurofilament-, GAP-43-, anti-calcitonin gene-related peptide (CGRP)-, and serotonin-immunoreactive fibers traversed the glial scars formed at both cord-graft interfaces. Supraspinal serotonergic axons crossed the transection gap through connective tissue bridges formed on the exterior of the channels, avoiding the channel interior. Strikingly, after crossing the distal glial scar, these fibers elongated in white and periaqueductal gray matter, reaching the farthest distance analyzed (1.5 cm). Tracer-labeled axons present in SC grafts were found to extend across the distal interface and up to 800 microm beyond in the distal cord. Long-distance regeneration (at least 2.5 cm) of injured ascending propriospinal axons was observed in the rostral spinal cord. Transplanted EG migrated longitudinally and laterally from the injection sites, reaching the farthest distance analyzed (1.5 cm). They moved through white matter tracts, gray matter, and glial scars, overcoming the inhibitory nature of the CNS environment, and invaded SC and connective tissue bridges and the dorsal and ventral roots adjacent to the transection site. Transplanted EG and regenerating axons were found in the same locations. Because EG seem to provide injured spinal axons with appropriate factors for long-distance elongation, these cells offer new possibilities for treatment of CNS conditions that require axonal regeneration.     

Neurotrophic factors increase axonal growth after spinal cord injury and transplantation in the adult rat

The capacity of CNS neurons for axonal regrowth after injury decreases as the age of the animal at time of injury increases. After spinal cord lesions at birth, there is extensive regenerative growth into and beyond a transplant of fetal spinal cord tissue placed at the injury site. After injury in the adult, however, although host corticospinal and brainstem-spinal axons project into the transplant, their distribution is restricted to within 200 micron of the host/transplant border. The aim of this study was to determine if the administration of neurotrophic factors could increase the capacity of mature CNS neurons for regrowth after injury. Spinal cord hemisection lesions were made at cervical or thoracic levels in adult rats. Transplants of E14 fetal spinal cord tissue were placed into the lesion site. The following neurotrophic factors were administered at the site of injury and transplantation: brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), neurotrophin-4 (NT-4), ciliary-derived neurotrophic factor (CNTF), or vehicle alone. After 1-2 months survival, neuroanatomical tracing and immunocytochemical methods were used to examine the growth of host axons within the transplants. The neurotrophin administration led to increases in the extent of serotonergic, noradrenergic, and corticospinal axonal ingrowth within the transplants. The influence of the administration of the neurotrophins on the growth of injured CNS axons was not a generalized effect of growth factors per se, since the administration of CNTF had no effect on the growth of any of the descending CNS axons tested. These results indicate that in addition to influencing the survival of developing CNS and PNS neurons, neurotrophic factors are able to exert a neurotropic influence on injured mature CNS neurons by increasing their axonal growth within a transplant.     

Regeneration of adult axons in white matter tracts of the central nervous system

It is widely accepted that the adult mammalian central nervous system (CNS) is unable to regenerate axons. In addition to physical or molecular barriers presented by glial scarring at the lesion site, it has been suggested that the normal myelinated CNS environment contains potent growth inhibitors or lacks growth-promoting molecules. Here we investigate whether adult CNS white matter can support long-distance regeneration of adult axons in the absence of glial scarring, by using a microtransplantation technique that minimizes scarring to inject minute volumes of dissociated adult rat dorsal root ganglia directly into adult rat CNS pathways. This atraumatic injection procedure allowed considerable numbers of regenerating adult axons immediate access to the host glial terrain, where we found that they rapidly extended for long distances in white matter, eventually invading grey matter. Abortive regeneration correlated precisely with increased levels of proteoglycans within the extracellular matrix at the transplant interface, whereas successfully regenerating transplants were associated with minimal upregulation of these molecules. Our results demonstrate, to our knowledge for the first time, that reactive glial extracellular matrix at the lesion site is directly associated with failure of axon regrowth in vivo, and that adult myelinated white matter tracts beyond the glial scar can be highly permissive for regeneration.     

Astrocytes and extracellular matrix following intracerebral transplantation of embryonic ventral mesencephalon or lateral ganglionic eminence

Transplantation of embryonic neurons to the adult mammalian central nervous system (CNS) offers the possibility of re-establishing neural functions lost after traumatic injuries or neurodegenerative disease. In the adult CNS, however, transplanted neurons and their growing neurites can become confined to the graft region, and there may also be a relative paucity of afferents innervating grafted neurons. Because glia may influence the development and regeneration of CNS neurons, the present study has characterized the distribution of astrocytes and developmentally regulated glycoconjugates (chondroitin-6-sulfate proteoglycan and tenascin) within regions of the embryonic mouse CNS used as donor tissues, and in and around these grafts to the adult striatum and substantia nigra. Both chondroitin-6-sulfate proteoglycan and tenascin are present in the embryonic ventral mesencephalon (in association with radial glia and their endfeet, and glial boundaries that cordon off the ventral mesencephalon dopamine neuron migratory zone) and lateral ganglionic eminence before transplantation, and they are conserved within grafts of these tissues to the adult mouse. Neostriatal grafts exhibit a heterogeneous pattern of astrocyte and extracellular matrix molecule distribution, unlike ventral mesencephalon grafts, which are rather homogeneous. There is evidence to suggest that, in addition to variation in astroglial/extracellular matrix immunostaining within different compartments in striatal grafts to either adult striatum or substantia nigra, there are also boundaries between these compartments that are rich in glial fibrillary acidic protein/extracellular matrix components. Substantia nigra grafts, with cells immunoreactive for tyrosine hydroxylase, are also rich in immature astroglia (RC-2-immunopositive), and as the astroglia mature (to glial fibrillary acidic protein-positive) over time the expression of chondroitin-6-sulfate proteoglycan and tenascin is also reduced. These same extracellular matrix constituents, however, are only slightly up-regulated in an area of the adult host which surrounds the grafted tissue. Glial scar components exhibit no obvious differences between grafts from different sources to homotopic (e.g., striatum to striatum) or heterotopic (e.g., substantia nigra to striatum) sites, and likewise grafts of non-synaptically associated structures (e.g., cerebellum to striatum), needle lesions or vehicle injections all yield astroglial/extracellular matrix scars in the host that are indistinguishable. Studies utilizing the ROSA-26 transgenic (beta-galactosidase-positive) mouse as a host for non-5-bromo-4-chloro-3-indolyl-beta-d-galactopyranoside-labeled grafts indicate that the early astroglial/extracellular matrix response to the graft is derived from the surrounding host structures. Furthermore, biochemical analysis of one of the "boundary molecules", tenascin, from the developing ventral mesencephalon versus adult striatal lesions, suggests that different forms of the molecule predominate in the embryonic versus lesioned adult brain. Such differences in the nature and distribution of astroglia and developmentally regulated extracellular matrix molecules between donor and host regions may affect the growth and differentiation of transplanted neurons. The present study suggests that transplanted neurons and their processes may flourish within graft versus host regions, in part due to a confining glial scar, but also because the extracellular milieu within the graft site remains more representative of the developmental environment from which the donor neurons were obtained [Gates M. A., et al. (1994) Soc. Neurosci. Abstr. 20, 471].     

Transplanted olfactory ensheathing cells remyelinate and enhance axonal conduction in the demyelinated dorsal columns of the rat spinal cord

Olfactory ensheathing cells (OECs), which have properties of both astrocytes and Schwann cells, can remyelinate axons with a Schwann cell-like pattern of myelin. In this study the pattern and extent of remyelination and the electrophysiological properties of dorsal column axons were characterized after transplantation of OECs into a demyelinated rat spinal cord lesion. Dorsal columns of adult rat spinal cords were demyelinated by x-ray irradiation and focal injections of ethidium bromide. Cell suspensions of acutely dissociated OECs from neonatal rats were injected into the lesion 6 d after x-ray irradiation. At 21-25 d after transplantation of OECs, the spinal cords were maintained in an in vitro recording chamber to study the conduction properties of the axons. The remyelinated axons displayed improved conduction velocity and frequency-response properties, and action potentials were conducted a greater distance into the lesion, suggesting that conduction block was overcome. Quantitative histological analysis revealed remyelinated axons near and remote from the cell injection site, indicating extensive migration of OECs within the lesion. These data support the conclusion that transplantation of neonatal OECs results in quantitatively extensive and functional remyelination of demyelinated dorsal column axons.     

Estimating the costs of hip fracture and potential savings

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.     

Validation of computerized Swedish dog and cat insurance data against veterinary practice records

Spontaneous cellular reorganisation at the lesion site has been investigated following massive spinal cord compression injury in adult rats. By 2 days post operation (p.o.), haemorrhagic necrosis, widespread axonal degeneration, and infiltration by polymorphnuclear granulocytes and OX42-positive macrophages were observed in the lesion site. By 7 days p.o., low affinity nerve growth factor receptor-positive Schwann cells, from activated spinal roots, were identified as they migrated far into the lesion. Between 7 and 14 days p.o., the overlapping processes of Schwann cells within the macrophage-filled lesion formed a glial framework which was associated with extensive longitudinally orientated ingrowth by many neurofilament-positive axons. Relatively few of these axons were calcitonin gene-related peptide (CGRP)-, substance P (SP)-, or serotonin (5HT)-positive; however, many were glycinergic or gamma aminobutyric acid (GABA)ergic. At 21 and 28 days p.o. (the longest survival times studied), a reduced but still substantial amount of orientated Schwann cells and axons could be detected at distances of up to 5 mm within the lesion. Glial fibrillary acidic protein (GFAP) immunoreactivity demonstrated the slow formation of astrocytic scarring which only became apparent at the lesion interface between 21 and 28 days p.o. The current data suggest the possibility of developing future therapeutic strategies designed to maintain or even enhance these spontaneous and orientated regenerative events.     

Development of long-distance efferent projections from fetal hippocampal grafts depends upon pathway specificity and graft location in kainate-lesioned adult hippocampus

Fetal hippocampal cells grafted into the excitotoxically lesioned hippocampus of adult rats are capable of extending axonal projections into the host brain. We hypothesize that the axonal growth of grafted fetal cells into specific host targets, and the establishment of robust long-distance efferent graft projections, require placement of fetal cells in close proximity to appropriate axon guidance pathways. Intracerebroventricular administration of kainic acid in adult rats leads to a specific loss of hippocampal CA3 pyramidal neurons. We grafted 5'-bromodeoxyuridine-labeled embryonic day 19 hippocampal cells into adult hippocampus at four days post-kainic acid lesion, and quantitatively measured the projection of grafted cells into the contralateral hippocampus and the septum after three to four months survival using Fluoro-Gold and 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine (Dil) tracing. Grafts located in or near the degenerated CA3 cell layer exhibited numerous neurons which established commissural projections with the contralateral hippocampus. However, such projection did not occur in intrahippocampal grafts located away from the CA3 cell layer. In contrast, neurons in all grafts established robust projections into the septum regardless of location within hippocampus although grafts located near the degenerated CA3 cell layer displayed more neurons with such projections. Location of grafted cells clearly influences the development of efferent graft projections into distant targets in the adult host brain, particularly access to axon guidance pathways to facilitate the formation of projections. The establishment of robust long-distance commissural projections of fetal hippocampal grafts is clearly dependent on their placement in or near the degenerated CA3 cell layer, suggesting that appropriate axon guidance pathways for commissural pathways are tightly focussed near this cell layer. However, the establishment of septal projections of these grafts was not dependent on specific location within the CA3 cell layer, suggesting that axonal guidance mechanisms to the septum are more diffuse and not limited to the CA3 dendritic layers. The results underscore that fetal hippocampal grafts are capable of partly restoring lesioned hippocampal circuitry in adult animals when appropriately placed in the host hippocampus.     

Sprouting adult CNS cholinergic axons express NILE and associate with astrocytic surfaces expressing neural cell adhesion molecule

To assess the cellular and molecular substrates for cholinergic axon growth in the adult central nervous system (CNS), we implanted grafts of control and nerve growth factor (NGF)-producing genetically modified fibroblasts within the striatum of rats. Sprouting cholinergic axonal processes that grew into grafts of NGF-producing fibroblasts were fasciculated and followed the surface of astrocytic processes for long distances within the grafts. The close and long distance anatomical relationship between the sprouted axons and the astrocytes supported previous ultrastructural evidence that astrocytes may serve as a cellular substrate for sprouting cholinergic axons in vivo. The sprouted axon processes were associated with the expression of nerve growth factor-inducible large external (NILE) glycoprotein on their surfaces. NILE expression was not seen in control grafts where there was an absence of cholinergic ingrowth. NILE has been demonstrated to play a role in axon fasciculation in a number of other neural systems. The astrocytic processes in both control and NGF-producing fibroblast grafts expressed neural cell adhesion molecule (NCAM), suggesting that NCAM-mediated adhesion may be responsible for the close relationship between the axons and astrocytes within the grafts. NGF-induced heterotypic interactions between neuronal NILE and astroglial NCAM may also be required for adult cholinergic axonal sprouting.     

Chimeric brain: theoretical and clinical aspects

Using xeno-transplantation, interactions of neural tissues of vertebrates and insects were studied. Ventral neurogenic primordium of Notch Drosophila melanogaster embryos was transplanted into neural tube of amphibian and mammalian embryos with the aid of microhydrofeeding. Embryos of four different amphibian species, random bred mice and rats were used as graft recipients. It was concluded that there is a possibility to incorporate nerve cells of insects into the brain of vertebrates. Morphological and functional contacts can be established between the transplanted cells and host brain tissues. Transplanted Drosophila cells preserve their viability for a long time, so that a prolonged influence of the transplant upon the recipient can be predicted, which may be used in medical practice. A mixture of human fetal brain and Notch Drosophila melanogaster neural embryonic tissues were transplanted into the ventro-lateral nucleus of the thalamus of the patients of Parkinson' disease. As a result, tremor and constrained movements disappeared. Post-operation patients have been observed within 13-38 months. No side effects were noted during this time.     

Extending the range of rate constants available from BIACORE: interpreting mass transport-influenced binding data

Myelin-associated inhibitors of neurite growth play an important role in the regenerative failure after injury in the adult mammalian CNS. The application of the mAb IN-1, which efficiently neutralizes the NI-250/35 inhibitory proteins, alone or in combination with neurotrophin-3 (NT-3), has been shown to promote axonal regeneration when applied in acute injury models. To test whether IN-1 application can induce axonal growth also in a chronic injury model, we treated rats with IN-1 and NT-3 starting 2 or 8 weeks after injury. Rats underwent bilateral dorsal hemisection of the spinal cord at the age of 5-6 weeks. Regeneration of corticospinal (CST) fibers into the caudal spinal cord was observed in three of eight of those animals with a 2-week delay between lesion and treatment. CST fibers regenerated for 2-11.4 mm. In the control group sprouting occurred rostral to the lesion but no long-distance regeneration occurred. In animals where treatment started at 8 weeks after injury the longest fibers observed grew up to 2 mm into the caudal spinal cord. The results show that transected corticospinal axons retain the ability to regenerate at least for a few weeks after injury. Functional analysis of these animals showed a slight improvement of functional recovery.     

Use of Schwann cells to induce repair of adult CNS tracts

The ability of transplanted Schwann cells to modify the sprouts formed by cut central axons, and in particular to induce branching and extension of axon sprouts, is an encouraging sign for their possible future use in repair. The accessibility of the Schwann cells in the culture stage before transplantation offers a practical opportunity for genetic engineering (e.g. to introduce genes directing the expression of specific growth factors) which might be useful in designing a future method for the repair of human spinal injury. It must be borne in mind, however, that even the most successful cases of peripheral nerve grafts have shown only a limited proportion of axons growing back from the grafts into the environment of the CNS (Carter et al., 1989). When we constructed Schwann cells transplanted into the thalamus (Brook et al., 1994), we did not observe axons leaving the artificial tracts. In our experiments with Schwann cells transplanted into the spinal cord (Li & Raisman, 1994), the axons have only been studied within the graft, and we have as yet not been able to assess the extent to which they re-enter the CNS. For effective regeneration to occur, regenerating axons must not only be able to re-enter their original pathways and elongate along them, but also leave them in a correct manner--i.e. by making appropriate choices from a wide range of destinations. Therefore the effectiveness of a Schwann cell "bridging" repair must depend upon the self-organising capacity of the adult CNS (e.g. Florence et al., 1996).     

Conditionally immortalized neural progenitor cells grafted to the striatum exhibit site-specific neuronal differentiation and establish connections with the host globus pallidus

The cell line RN33B has been reported to differentiate into neurons in a site-specific manner when grafted to the cortex and hippocampus of adult rats. To investigate the fate of RN33B cells in a subcortical structure, we grafted RN33B cells into the intact or excitoxically lesioned striatum of adult or neonatal rats. The total number and phenotypic characteristics of the [3H]thymidine-labeled grafted cells were analyzed at different time points after transplantation. Transplanted RN33B cells were found to survive, integrate, and differentiate into both neurons and astrocytes, and a significant proportion of the cells (approx. 10%) were found to differentiate into cells with morphological and phenotypic characteristics of medium-sized striatal projection neurons. Retrograde tracing showed that at least some of the graft-derived neurons were capable of establishing connections with one of the primary striatal targets, the globus pallidus. These findings demonstrate a remarkable capacity of the RN33B cells for site-specific neuronal differentiation in both the adult and the developing striatum and suggest that the same differentiating factors that are operating during normal neurogenesis in brain development are retained, at least to some extent, also in the adult CNS.     

Anatomical evidence for a mechanism of lateral inhibition in the rat thalamus

The aim of this study was to determine whether or not thalamic reticular nucleus (Rt) neurons form synaptic connections with the thalamocortical (TC) neurons from which they receive synaptic contacts. Therefore, we examined, in adult rats, the relationships between single TC and Rt neurons, which had been marked simultaneously with an anterograde/retrograde tracer (biocytin or Neurobiotin), using the extracellular or juxtacellular technique. (i) From 30 successful extracellular microapplications of marker into the Rt, 22 gave retrogradely marked TC somatodendritic arbors at the fringe of or clear outside the anterogradely darkly stained Rt axon terminal fields. Following biocytin application into the thalamus, few cells were retrogradely stained in the Rt at the periphery of the anterogradely labelled axon terminal field. (ii) The juxtacellular filling of a single Rt cell was accompanied by the back-filling of a single TC neuron (n = 4 pairs), which presumably formed synaptic contacts with the former cell. The somatodendritic complex of the back-filled TC neuron was located outside the Rt cell's axonal arbor. These anatomical data provide clear evidence that Rt and thalamic neurons predominantly form between themselves open rather than closed loop connections. Because TC neurons make glutamatergic synapses onto Rt cells, which are GABAergic, and are the first elements synaptically activated by prethalamic afferents into the TC-Rt network, the present results strongly support the hypothesis that Rt neurons principally generate a mechanism of lateral inhibition in the thalamus.     

Regeneration of ascending spinal axons in goldfish

Regeneration of descending spinal cord tracts occur spontaneously in adult goldfish. Very little information is available regarding the fate of ascending fibers. Using Dextran amines as a tracer, we studied the normal and regenerated ascending axonal projection patterns in adult goldfish brain nuclei. Present study includes spinal projections to torus semicircularis, hypothalamus, thalamus and the telencephalon. Regenerated fibers had finer caliber axons and the terminal axonal arbors covered a larger area than the corresponding normal ones.     

Human dorsal root ganglion neurons from embryonic donors extend axons into the host rat spinal cord along laminin-rich peripheral surroundings of the dorsal root transitional zone

Following dorsal root crush, the lesioned axons regenerate in the peripheral compartment of the dorsal root, but stop at the boundary between the peripheral and the central nervous system, the dorsal root transitional zone. We have previously shown that fibres from human fetal dorsal root ganglia grafted to adult rat hosts are able to grow into the spinal cord, but were not able to specify the route taken by the ingrowing fibres. In this study we have challenged the dorsal root transitional zone astrocyte boundary with human dorsal root ganglion transplants from 5-8-week-old embryos. By tracing immunolabelled human fibres in serial sections, we found that fibres consistently grow around the dorsal root transitional zone astrocytes in laminin-rich peripheral surroundings, and extend into the host rat spinal cord along blood vessels, either into deep or superficial laminae of the dorsal horn, or into the dorsal funiculus. Human fibres that did not have access to blood vessels grew on the spinal cord surface. These findings indicate, that in spite of a substantial growth capacity by axons from human embryonic dorsal root ganglion cells as well as their tolerance to non-permissive factors in the mature mammalian CNS, these axons are still sensitive to the repellent effects of astrocytes of the mature dorsal root transitional zone. Furthermore, this axonal ingrowth is consistently associated with laminin-expressing structures until the axons reach the host spinal cord.     

Neural injury repair: hope for the future as barriers to effective CNS regeneration become clearer

In this review the author outlines the early history of clinical and scientific research upon the inability of the CNS in man to successfully regenerate following injury. As we proceed into the 21st Century we have gained a far greater understanding of the molecular biology, pathology and other factors that lead to the adult CNS being non-supportive and indeed actively inhibitory to axonal regrowth. On the basis of these recent advances in knowledge, the author outlines possible therapeutic approaches that may enable more effective CNS regeneration to be accomplished in the future.     

Intrahypothalamic injection of a cell line secreting gonadotropin-releasing hormone results in cellular differentiation and reversal of hypogonadism in mutant mice

GT1 is an immortalized cell line that synthesizes and secretes the neurohormone gonadotropin-releasing hormone (GnRH). We have placed these cells into the brains of adult mutant hypogonadal (hpg) mice, which lack a functional GnRH gene, to determine whether such cells could differentiate in situ and support gonadal development. Immunocytochemical detection of GnRH revealed that these cells migrated widely in the central nervous system and elaborated axonal processes which on rare occasion projected to the normal target, the median eminence. Using a battery of antibodies, we demonstrated that these cells could cleave the GnRH precursor and that the amidated decapeptide as well as other cleavage products were present. The presence of biologically active material and its appropriate secretion were further documented by gonadal growth in both males and females. The morphological differentiation of the GT1 cells correlated with the density of cells injected. Those remaining within the injection site and/or forming a tumor retained a simple, rounded or fibroblastic appearance. Those cells that migrated into the host away from such tumors assumed the simple fusiform shape of normal GnRH neurons with dendrites extending from one or both poles. When cell density was drastically reduced a much more complex dendritic arbor was elaborated. These data suggest that such cell lines can be useful in reversing genetic defects and in studying such processes as GnRH neuronal migration, axonal targeting, and cytological differentiation.     

Comparison of the growth and fate of fetal spinal iso- and allografts in the adult rat injured spinal cord

Most studies investigating early fetal CNS graft-host interactions and host immune responses have been performed using intracerebral transplantation paradigms. The purpose of this study was to establish the early developmental dynamics of fetal graft integration with the injured host spinal cord and to determine whether fetal allografts in this environment are subject to rejection. ACI rat fetal spinal cord (FSC) tissue was grafted into acute lesion cavities of adult WF rat spinal cords. Graft development and/or rejection was followed from 1 to 45 days posttransplantation with morphometric, histological, and immunocytochemical methods. We determined that all FSC grafts in acute resection lesions of the adult rat spinal cord undergo an early substantial cellular attrition, but following favorable attachment to healthy host tissue margins, they rebound and grow to fill the lesion cavity by approximately 45 days. We also determined that FSC allografts into nonimmunosuppressed adult recipients are consistently rejected, but only after an early period of growth and maturation. The onset of rejection is characterized by extensive cellular infiltration coincidental with graft and host MHC antigen expression. The implications of delayed graft development and graft-host integration are discussed relative to interconnectivity and long-term potential for graft-derived benefits. The observed rejection response was characteristic of first-order allograft rejection and underscores a lack of immunological privilege in the microenvironment of the injured spinal cord.     

Cytomorphological changes in the rabbit oviductal epithelium after human chorionic gonadotropin treatment

Progenitor cells were isolated from the developing human central nervous system (CNS), induced to divide using a combination of epidermal growth factor and fibroblast growth factor-2, and then transplanted into the striatum of adult rats with unilateral dopaminergic lesions. Large grafts were found at 2 weeks survival which contained many undifferentiated cells, some of which were migrating into the host striatum. However, by 20 weeks survival, only a thin strip of cells remained at the graft core while a large number of migrating astrocytes labeled with a human-specific antibody could be seen throughout the striatum. Fully differentiated graft-derived neurons, also labeled with a human-specific antibody, were seen close to the transplant site in some animals. A number of these neurons expressed tyrosine hydroxylase and were sufficient to partially ameliorate lesion-induced behavioral deficits in two animals. These results show that expanded populations of human CNS progenitor cells maintained in a proliferative state in culture can migrate and differentiate into both neurons and astrocytes following intracerebral grafting. As such these cells may have potential for development as an alternative source of tissue for neural transplantation in degenerative diseases.