Development of embryonic spinal cord transplants in the rat

Developmental stage of transplanted neural progenitor cells influences anatomical and functional outcomes after spinal cord injury in mice

Neural progenitor cell (NPC) transplantation is a promising therapeutic strategy for replacing lost neurons following spinal cord injury (SCI). However, how graft cellular composition influences regeneration and synaptogenesis of host axon populations, or recovery of motor and sensory functions after SCI, is poorly understood. We transplanted developmentally-restricted spinal cord NPCs, isolated from E11.5-E13.5 mouse embryos, into sites of adult mouse SCI and analyzed graft axon outgrowth, cellular composition, host axon regeneration, and behavior. Earlier-stage grafts exhibited greater axon outgrowth, enrichment for ventral spinal cord interneurons and Group-Z spinal interneurons, and enhanced host 5-HT+ axon regeneration. Later-stage grafts were enriched for late-born dorsal horn interneuronal subtypes and Group-N spinal interneurons, supported more extensive host CGRP+ axon ingrowth, and exacerbated thermal hypersensitivity. Locomotor function was not affected by any type of NPC graft. These findings showcase the role of spinal cord graft cellular composition in determining anatomical and functional outcomes following SCI.

Locally controlled release of immunosuppressive promotes survival of transplanted adult spinal cord tissue

Transplantation of adult spinal cord tissue (aSCT) is a promising treatment for spinal cord injury (SCI) basing on various types of neural cells and matrix components inside aSCT. However, long-term systemic administration of immunosuppressors (e.g. tacrolimus, TAC) is required for the survival of allogeneic tissue, which often associated with severe side effects such as infection, liver damageand renal failure. In this study, a triglycerol monostearate (TGM)-based TAC delivery system (e.g. TAC@TGM) with high drug loading concentration was developed, which possessed injectable properties as well as sustainable and immune-responsive drug release behaviors. In complete transected SCI model, locally injected TAC@TGM could reduce the infiltration of inflammation cells, enhance the survival of transplanted aSCT (e.g. Tuj-1⁺ and NF⁺ neurons) and promote the recovery of locomotor function. Moreover, controlled release of TAC by TAC@TGM attenuated side effects of TAC on liver and kidneys compared with traditional systemic administration. More importantly, the developed TAC@TGM system provided a facile single dose of long-term immunosuppressive effect not just for aSCT transplantation, but also for other tissue/organ and cell transplantations.

Effects of biological sex mismatch on neural progenitor cell transplantation for spinal cord injury in mice

Despite advancement of neural progenitor cell transplantation to spinal cord injury clinical trials, there remains a lack of understanding of how biological sex of transplanted cells influences outcomes after transplantation. To address this, we transplanted GFP-expressing sex-matched, sex-mismatched, or mixed donor cells into sites of spinal cord injury in adult male and female mice. Biological sex of the donor cells does not influence graft neuron density, glial differentiation, formation of the reactive glial cell border, or graft axon outgrowth. However, male grafts in female hosts feature extensive hypervascularization accompanied by increased vascular diameter and perivascular cell density. We show greater T-cell infiltration within male-to-female grafts than other graft types. Together, these findings indicate a biological sex-specific immune response of female mice to male donor cells. Our work suggests that biological sex should be considered in the design of future clinical trials for cell transplantation in human injury.

In this study, Pitonak et al. report that transplantation of neural progenitor cells derived from male donors trigger an immune rejection response following transplantation into sites of spinal cord injury in female mice.

Preparation of Neural Stem Cells and Progenitors: Neuronal Production and Grafting Applications

Neural stem cells (NSCs) are a valuable tool for the study of neural development and function as well as an important source of cell transplantation strategies for neural disease. NSCs can be used to study how neurons acquire distinct phenotypes and how the interactions between neurons and glial cells in the developing nervous system shape the structure and function of the CNS. NSCs can also be used for cell replacement therapies following CNS injury targeting astrocytes, oligodendrocytes, and neurons. With the availability of patient-derived induced pluripotent stem cells (iPSCs), neurons prepared from NSCs can be used to elucidate the molecular basis of neurological disorders leading to potential treatments. Although NSCs can be derived from different species and many sources, including embryonic stem cells (ESCs), iPSCs, adult CNS, and direct reprogramming of nonneural cells, isolating primary NSCs directly from fetal tissue is still the most common technique for preparation and study of neurons. Regardless of the source of tissue, similar techniques are used to maintain NSCs in culture and to differentiate NSCs toward mature neural lineages. This chapter will describe specific methods for isolating and characterizing multipotent NSCs and neural precursor cells (NPCs) from embryonic rat CNS tissue (mostly spinal cord) and from human ESCs and iPSCs as well as NPCs prepared by reprogramming. NPCs can be separated into neuronal and glial restricted progenitors (NRP and GRP, respectively) and used to reliably produce neurons or glial cells both in vitro and following transplantation into the adult CNS. This chapter will describe in detail the methods required for the isolation, propagation, storage, and differentiation of NSCs and NPCs isolated from rat and mouse spinal cords for subsequent in vitro or in vivo studies as well as new methods associated with ESCs, iPSCs, and reprogramming.

Allotransplantation of adult spinal cord tissues after complete transected spinal cord injury: Long-term survival and functional recovery in canines

Spinal cord injury (SCI), especially complete transected SCI, leads to loss of cells and extracellular matrix and functional impairments. In a previous study, we transplanted adult spinal cord tissues (aSCTs) to replace lost tissues and facilitate recovery in a rat SCI model. However, rodents display considerable differences from human patients in the scale, anatomy and functions of spinal cord systems, and responses after injury. Thus, use of a large animal SCI model is required to examine the repair efficiency of potential therapeutic approaches. In this study, we transplanted allogenic aSCTs from adult dogs to the lesion area of canines after complete transection of the thoracic spinal cord, and investigated the long-term cell survival and functional recovery. To enhance repair efficiency, a growth factor cocktail was added during aSCT transplantation, providing a favorable microenvironment. The results showed that transplantation of aSCTs, in particular with the addition of growth factors, significantly improves locomotor function restoration and increases the number of neurofilament-, microtubule-associated protein 2-, 5-hydroxytryptamine-, choline acetyltransferase- and tyrosine hydroxylase-positive neurons in the lesion area at 6 months post-surgery. In addition, we demonstrated that donor neurons in aSCTs can survive for a long period after transplantation. This study showed for the first time that transplanting aSCTs combined with growth factor supplementation facilitates reconstruction of injured spinal cords, and consequently promotes long lasting motor function recovery in a large animal complete transected SCI model, and therefore could be considered as a possible therapeutic strategy in humans.

Transsynaptic tracing and its emerging use to assess graft-reconstructed neural circuits

Fetal neural progenitor grafts have been evaluated in preclinical animal models of spinal cord injury and Parkinson's disease for decades, but the initial reliance on primary tissue as a cell source limited the scale of their clinical translatability. With the development of robust methods to differentiate human pluripotent stem cells to specific neural subtypes, cell replacement therapy holds renewed promise to treat a variety of neurodegenerative diseases and injuries at scale. As these cell sources are evaluated in preclinical models, new transsynaptic tracing methods are making it possible to study the connectivity between host and graft neurons with greater speed and detail than was previously possible. To date, these studies have revealed that widespread, long-lasting, and anatomically appropriate synaptic contacts are established between host and graft neurons, as well as new aspects of host-graft connectivity which may be relevant to clinical cell replacement therapy. It is not yet clear, however, whether the synaptic connectivity between graft and host neurons is as cell-type specific as it is in the endogenous nervous system, or whether that connectivity is responsible for the functional efficacy of cell replacement therapy. Here, we review evidence suggesting that the new contacts established between host and graft neurons may indeed be cell-type specific, and how transsynaptic tracing can be used in the future to further elucidate the mechanisms of graft-mediated functional recovery in spinal cord injury and Parkinson's disease.

Transplanting Cells for Spinal Cord Repair: Who, What, When, Where and Why?

Cellular transplantation for repair of the injured spinal cord has a rich history with strategies focused on neuroprotection, immunomodulation, and neural reconstruction. The goal of the present review is to provide a concise overview and discussion of five key themes that have become important considerations for rebuilding functional neural networks. The questions raised include: (i) who are the donor cells selected for transplantation, (ii) what is the intended target for repair, (iii) when is the optimal time for transplantation, (iv) where should the cells be delivered, and lastly (v) why does cell transplantation remain an attractive candidate for promoting neural repair after injury? Recent developments in neurobiology and engineering now enable us to start addressing these questions with multidisciplinary expertise and methods.

Transplantation of Neural Progenitors and V2a Interneurons after Spinal Cord Injury

There is growing interest in the use of neural precursor cells to treat spinal cord injury (SCI). Despite extensive pre-clinical research, it remains unclear as to which donor neuron phenotypes are available for transplantation, whether the same populations exist across different sources of donor tissue (e.g., developing tissue vs. cultured cells), and whether donor cells retain their phenotype once transplanted into the hostile internal milieu of the injured adult spinal cord. In addition, while functional improvements have been reported after neural precursor transplantation post-SCI, the extent of recovery is limited and variable. The present work begins to address these issues by harnessing ventrally derived excitatory pre-motor V2a spinal interneurons (SpINs) to repair the phrenic motor circuit after cervical SCI. Recent studies have demonstrated that Chx10-positive V2a SpINs contribute to anatomical plasticity within the phrenic circuitry after cervical SCI, thus identifying them as a therapeutic candidate. Building upon this discovery, the present work tests the hypothesis that transplantation of neural progenitor cells (NPCs) enriched with V2a INs can contribute to neural networks that promote repair and enhance respiratory plasticity after cervical SCI. Cultured NPCs (neuronal and glial restricted progenitor cells) isolated from E13.5 Green fluorescent protein rats were aggregated with TdTomato-mouse embryonic stem cell-derived V2a INs in vitro, then transplanted into the injured cervical (C3-4) spinal cord. Donor cells survive, differentiate and integrate with the host spinal cord. Functional diaphragm electromyography indicated recovery 1 month following treatment in transplant recipients. Animals that received donor cells enriched with V2a INs showed significantly greater functional improvement than animals that received NPCs alone. The results from this study offer insight into the neuronal phenotypes that might be effective for (re)establishing neuronal circuits in the injured adult central nervous system.

Integration of Transplanted Neural Precursors with the Injured Cervical Spinal Cord

Cervical spinal cord injuries (SCI) result in devastating functional consequences, including respiratory dysfunction. This is largely attributed to the disruption of phrenic pathways, which control the diaphragm. Recent work has identified spinal interneurons as possible contributors to respiratory neuroplasticity. The present work investigated whether transplantation of developing spinal cord tissue, inherently rich in interneuronal progenitors, could provide a population of new neurons and growth-permissive substrate to facilitate plasticity and formation of novel relay circuits to restore input to the partially denervated phrenic motor circuit. One week after a lateralized, C3/4 contusion injury, adult Sprague-Dawley rats received allografts of dissociated, developing spinal cord tissue (from rats at gestational days 13-14). Neuroanatomical tracing and terminal electrophysiology was performed on the graft recipients 1 month later. Experiments using pseudorabies virus (a retrograde, transynaptic tracer) revealed connections from donor neurons onto host phrenic circuitry and from host, cervical interneurons onto donor neurons. Anatomical characterization of donor neurons revealed phenotypic heterogeneity, though donor-host connectivity appeared selective. Despite the consistent presence of cholinergic interneurons within donor tissue, transneuronal tracing revealed minimal connectivity with host phrenic circuitry. Phrenic nerve recordings revealed changes in burst amplitude after application of a glutamatergic, but not serotonergic antagonist to the transplant, suggesting a degree of functional connectivity between donor neurons and host phrenic circuitry that is regulated by glutamatergic input. Importantly, however, anatomical and functional results were variable across animals, and future studies will explore ways to refine donor cell populations and entrain consistent connectivity.

Embryonic Cell Grafts in a Culture Model of Spinal Cord Lesion: Neuronal Relay Formation Is Essential for Functional Regeneration

Presently there exists no cure for spinal cord injury (SCI). However, transplantation of embryonic tissue into spinal cord (SC) lesions resulted in axon outgrowth across the lesion site and some functional recovery, fostering hope for future stem cell therapies. Although in vivo evidence for functional recovery is given, the exact cellular mechanism of the graft support remains elusive: either the grafted cells provide a permissive environment for the host tissue to regenerate itself or the grafts actually integrate functionally into the host neuronal network reconnecting the separated SC circuits. We tested the two hypotheses in an in vitro SC lesion model that is based on propagation of activity between two rat organotypic SC slices in culture. Transplantation of dissociated cells from E14 rat SC or forebrain (FB) re-established the relay of activity over the lesion site and thus, provoked functional regeneration. Combining patch-clamp recordings from transplanted cells with network activity measurements from the host tissue on multi-electrode arrays (MEAs) we here show that neurons differentiate from the grafted cells and integrate into the host circuits. Optogenetic silencing of neurons developed from transplanted embryonic mouse FB cells provides clear evidence that they replace the lost neuronal connections to relay and synchronize activity between the separated SC circuits. In contrast, transplantation of neurospheres (NS) induced neither the differentiation of mature neurons from the grafts nor an improvement of functional regeneration. Together these findings suggest, that the formation of neuronal relays from grafted embryonic cells is essential to re-connect segregated SC circuits.

Thermomineral water promotes axonal sprouting but does not reduce glial scar formation in a mouse model of spinal cord injury

Thermomineral water from the Atomic Spa Gornja Trepča has been used for a century in the treatment of neurologic disease. The thermomineral water contains microelements, including lithium and magnesium, which show neural regeneration-promoting effects after central nervous system injury. In this study, we investigated the effects of oral intake of thermomineral water from the Atomic Spa Gornja Trepča on nerve regeneration in a 3-month-old mouse model of spinal cord injury. The mice receiving oral intake of thermomineral water showed better locomotor recovery than those without administration of thermomineral water at 8 and 12 weeks after lower thoracic spinal cord compression. At 12 weeks after injury, sprouting of catecholaminergic axons was better in mice that drank thermomineral water than in those without administration of thermomineral water, but there was no difference in glial reaction to injury between mice with and without administration of thermomineral water. These findings suggest that thermomineral water can promote the nerve regeneration but cannot reduce glial scar formation in a mouse model of spinal cord injury.

Repair of spinal cord injury with neuronal relays: From fetal grafts to neural stem cells

Spinal cord injury (SCI) disrupts the long axonal tracts of the spinal cord leading to devastating loss of function. Cell transplantation in the injured spinal cord has the potential to lead to recovery after SCI via a variety of mechanisms. One such strategy is the formation of neuronal relays between injured long tract axons and denervated neurons. The idea of creating a neuronal relay was first proposed over 25 years ago when fetal tissue was first successfully transplanted into the injured rodent spinal cord. Advances in labeling of grafted cells and the development of neural stem cell culturing techniques have improved the ability to create and refine such relays. Several recent studies have examined the ability to create a novel neuronal circuit between injured axons and denervated targets. This approach is an alternative to long-distance regeneration of damaged axons that may provide a meaningful degree of recovery without direct recreation of lost pathways. This brief review will examine the contribution of fetal grafting to current advances in neuronal grafting. Of particular interest will be the ability of transplanted neurons derived from fetal grafts, neural precursor cells and neural stem cells to reconnect long distance motor and sensory pathways of the injured spinal cord. This article is part of a Special Issue entitled SI: Spinal cord injury.

Spinal cord regeneration

Three theories of regeneration dominate neuroscience today, all purporting to explain why the adult central nervous system (CNS) cannot regenerate. One theory proposes that Nogo, a molecule expressed by myelin, prevents axonal growth. The second theory emphasizes the role of glial scars. The third theory proposes that chondroitin sulfate proteoglycans (CSPGs) prevent axon growth. Blockade of Nogo, CSPG, and their receptors indeed can stop axon growth in vitro and improve functional recovery in animal spinal cord injury (SCI) models. These therapies also increase sprouting of surviving axons and plasticity. However, many investigators have reported regenerating spinal tracts without eliminating Nogo, glial scar, or CSPG. For example, many motor and sensory axons grow spontaneously in contused spinal cords, crossing gliotic tissue and white matter surrounding the injury site. Sensory axons grow long distances in injured dorsal columns after peripheral nerve lesions. Cell transplants and treatments that increase cAMP and neurotrophins stimulate motor and sensory axons to cross glial scars and to grow long distances in white matter. Genetic studies deleting all members of the Nogo family and even the Nogo receptor do not always improve regeneration in mice. A recent study reported that suppressing the phosphatase and tensin homolog (PTEN) gene promotes prolific corticospinal tract regeneration. These findings cannot be explained by the current theories proposing that Nogo and glial scars prevent regeneration. Spinal axons clearly can and will grow through glial scars and Nogo-expressing tissue under some circumstances. The observation that deleting PTEN allows corticospinal tract regeneration indicates that the PTEN/AKT/mTOR pathway regulates axonal growth. Finally, many other factors stimulate spinal axonal growth, including conditioning lesions, cAMP, glycogen synthetase kinase inhibition, and neurotrophins. To explain these disparate regenerative phenomena, I propose that the spinal cord has evolved regenerative mechanisms that are normally suppressed by multiple extrinsic and intrinsic factors but can be activated by injury, mediated by the PTEN/AKT/mTOR, cAMP, and GSK3b pathways, to stimulate neural growth and proliferation.

Transplanting neural progenitors into a complete transection model of spinal cord injury

Neural progenitor cell (NPC) transplantation is a promising therapeutic strategy for spinal cord injury (SCI) because of the potential for cell replacement and restoration of connectivity. Our previous studies have shown that transplants of NPC, composed of neuron- and glia-restricted progenitors derived from the embryonic spinal cord, survived well in partial lesion models and generated graft-derived neurons, which could be used to form a functional relay. We have now examined the properties of a similar NPC transplant using a complete transection model in juvenile and adult rats. We found poor survival of grafted cells despite using a variety of lesion methods, matrices, and delays of transplantation. If, instead of cultured progenitor cells, the transplants were composed of segmental or dissociated segments of fetal spinal cord (FSC) derived from similar-staged embryos, grafted cells survived and integrated well with host tissue in juvenile and adult rats. FSC transplants differentiated into neurons and glial cells, including astrocytes and oligodendrocytes. Graft-derived neurons expressed glutaminergic and GABAergic markers. Grafted cells also migrated and extended processes into host tissue. Analysis of axon growth from the host spinal cord showed serotonin-positive fibers and biotinylated dextran amine-traced propriospinal axons growing into the transplants. These results suggest that in treating severe SCI, such as complete transection, NPC grafting faces major challenges related to cell survival and formation of a functional relay. Lessons learned from the efficacy of FSC transplants could be used to develop a therapeutic strategy based on neural progenitor cells for severe SCI.

Auto-attraction of neural precursors and their neuronal progeny impairs neuronal migration

Limited neuronal migration into host brain tissue is a key challenge in neural transplantation. We found that one important mechanism underlying this phenomenon is an intrinsic chemotactic interaction between the grafted neural precursor cells (NPCs) and their neuronal progeny. NPCs secrete the receptor tyrosine kinase ligands FGF2 and VEGF, which act as chemoattractants for neurons. Interference with these signaling pathways resulted in enhanced migration of human neurons from neural clusters.

Sensory axon regeneration: rebuilding functional connections in the spinal cord

Functional regeneration within the adult spinal cord remains a formidable task. A major barrier to regeneration of sensory axons into the spinal cord is the dorsal root entry zone. This region displays many of the inhibitory features characteristic of other central nervous system injuries. Several experimental treatments, including inactivation of inhibitory molecules (such as Nogo and chondroitin sulfate proteoglycans) or administration of neurotrophic factors (such as nerve growth factor, neurotrophin3, glial-derived neurotrophic factor and artemin), have been found to promote anatomical and functional regeneration across this barrier. However, there have been relatively few experiments to determine whether regenerating axons project back to their appropriate target areas within the spinal cord. This review focuses on recent advances in sensory axon regeneration, including studies assessing the ability of sensory axons to reconnect with their original synaptic targets.

Cell Therapy From Bench to Bedside Translation in CNS Neurorestoratology Era

Recent advances in cell biology, neural injury and repair, and the progress towards development of neurorestorative interventions are the basis for increased optimism. Based on the complexity of the processes of demyelination and remyelination, degeneration and regeneration, damage and repair, functional loss and recovery, it would be expected that effective therapeutic approaches will require a combination of strategies encompassing neuroplasticity, immunomodulation, neuroprotection, neurorepair, neuroreplacement, and neuromodulation. Cell-based restorative treatment has become a new trend, and increasing data worldwide have strongly proven that it has a pivotal therapeutic value in CNS disease. Moreover, functional neurorestoration has been achieved to a certain extent in the CNS clinically. Up to now, the cells successfully used in preclinical experiments and/or clinical trial/treatment include fetal/embryonic brain and spinal cord tissue, stem cells (embryonic stem cells, neural stem/progenitor cells, hematopoietic stem cells, adipose-derived adult stem/precursor cells, skin-derived precursor, induced pluripotent stem cells), glial cells (Schwann cells, oligodendrocyte, olfactory ensheathing cells, astrocytes, microglia, tanycytes), neuronal cells (various phenotypic neurons and Purkinje cells), mesenchymal stromal cells originating from bone marrow, umbilical cord, and umbilical cord blood, epithelial cells derived from the layer of retina and amnion, menstrual blood-derived stem cells, Sertoli cells, and active macrophages, etc. Proof-of-concept indicates that we have now entered a new era in neurorestoratology.

Lineage-restricted neural precursors survive, migrate, and differentiate following transplantation into the injured adult spinal cord

Fetal spinal cord from embryonic day 14 (E14/FSC) has been used for numerous transplantation studies of injured spinal cord. E14/FSC consists primarily of neuronal (NRP)- and glial (GRP)-restricted precursors. Therefore, we reasoned that comparing the fate of E14/FSC with defined populations of lineage-restricted precursors will test the in vivo properties of these precursors in CNS and allow us to define the sequence of events following their grafting into the injured spinal cord. Using tissue derived from transgenic rats expressing the alkaline phosphatase (AP) marker, we found that E14/FSC exhibited early cell loss at 4 days following acute transplantation into a partial hemisection injury, but the surviving cells expanded to fill the entire injury cavity by 3 weeks. E14/FSC grafts integrated into host tissue, differentiated into neurons, astrocytes, and oligodendrocytes, and demonstrated variability in process extension and migration out of the transplant site. Under similar grafting conditions, defined NRP/GRP cells showed excellent survival, consistent migration out of the injury site and robust differentiation into mature CNS phenotypes, including many neurons. Few immature cells remained at 3 weeks in either grafts. These results suggest that by combining neuronal and glial restricted precursors, it is possible to generate a microenvironmental niche where emerging glial cells, derived from GRPs, support survival and neuronal differentiation of NRPs within the non-neurogenic and non-permissive injured adult spinal cord, even when grafted into acute injury. Furthermore, the NRP/GRP grafts have practical advantages over fetal transplants, making them attractive candidates for neural cell replacement.

Outgrowth of neurites from NIE-115 neuroblastoma cells is prevented on repulsive substrates through the action of PAK

In the central nervous system (CNS), damaged axons are inhibited from regeneration by glial scars, where secreted chondroitin sulfate proteoglycan (CSPG) and tenascin repulse outgrowth of neurites, the forerunners of axons and dendrites. During differentiation, these molecules are thought to form boundaries for guiding neurons to their correct targets. In neuroblastoma NIE-115 cells, outgrowth of neurites on laminin could be induced by serum starvation or inhibition of RhoA by Clostridium botulinum C3 toxin. The outgrowing neurites avoided crossing onto the repulsive substrate CSPG or tenascin. This avoidance response was partially overcome on expression of membrane-targeted and kinase-inactive forms of PAK. In these cells, the endogenous PAK isoforms colocalized with actin in distinctive sites, alphaPAK in the cell center as small clusters and along the neurite shaft and betaPAK and gammaPAK in areas with membrane ruffles and filopodia, respectively. When isoform-specific N-terminal PAK sequences were introduced to interfere with PAK function, substantially more neurites crossed onto CSPG when cells contained a gammaPAK-derived peptide but not the corresponding alphaPAK- or betaPAK-derived peptide. Thus, while neurite outgrowth can be promoted by RhoA inhibition, overcoming the accompanying repulsive guidance response will require modulation of PAK activity. These results have therapeutic implications for CNS repair processes.

An experimental model for the transplantation of fetal central nervous system cells to the injured spinal cord in rats

INTRODUCTION

Traumatic spinal cord injury is one of the most disabling conditions occurring in man and thus stimulates a strong interest in its histopathological, biochemical, and functional changes, primarily as we search for preventive and therapeutic methods.

PURPOSE

To develop an experimental model for transplantation of cells from the fetal rat central nervous system to the site of an injured spinal cord of an adult rat in which the transplanted cells survive and become integrated. This experimental model will facilitate investigations of factors that promote regeneration and functional recovery after spinal cord trauma.

MATERIAL AND METHODS

Fifteen adult Wistar rats underwent laminectomy, and an spinal cord lesion was made with microdissection. Fetal spinal cord tissue was then transplanted to the site of the injury. The rats were monitored over a 48-hour period, and then their vertebral column was completely removed for histological analysis.

RESULTS

In 60% of transplanted rats, the fetal tissue at the injured site remained viable in the site of the lesion.

Transplantation of in vitro-expanded fetal neural progenitor cells results in neurogenesis and functional recovery after spinal cord contusion injury in adult rats

Neural progenitor cells, including neural stem cells, are a potential expandable source of graft material for transplantation aimed at repairing the damaged CNS. Here we present the first evidence that in vitro-expanded fetus-derived neurosphere cells were able to generate neurons in vivo and improve motor function upon transplantation into an adult rat spinal-cord-contusion injury model. As the source of graft material, we used a neural stem cell-enriched population that was derived from rat embryonic spinal cord (E14.5) and expanded in vitro by neurosphere formation. Nine days after contusion injury, these neurosphere cells were transplanted into adult rat spinal cord at the injury site. Histological analysis 5 weeks after the transplantation showed that mitotic neurogenesis occurred from the transplanted donor progenitor cells within the adult rat spinal cord, a nonneurogenic region; that these donor-derived neurons extended their processes into the host tissues; and that the neurites formed synaptic structures. Furthermore, analysis of motor behavior using a skilled reaching task indicated that the treated rats showed functional recovery. These results indicate that in vitro-expanded neurosphere cells derived from the fetal spinal cord are a potential source for transplantable material for treatment of spinal cord injury.

Central nervous system regeneration: mission impossible?

1. Attempts to induce clinical repair after central nervous system injury, such as spinal cord damage, are likely to involve several protocols because eliciting a regenerative response from an injured central neuron is a complex task. Future treatments, applied when a window of opportunity exists, address the requirements for regeneration. 2. Application of trophic support to the lesion site for axotomized neurons aims to initiate and maintain a cell body response conducive to axonal regrowth. 3. Surgical intervention may provide a bridge across the injury site that contains either Schwann cells or olfactory bulb ensheathing cells derived from the patient's own tissue. 4. The application of antibodies may block the inhibitory action of myelin-associated molecules and other glial elements. 5. Gene therapy may induce the correct cascade of guidance molecules to be released at appropriate times. 6. Physical rehabilitation may ensure that muscle wastage is reduced and encourages functional reconnection.

Reinnervation of the biceps brachii muscle following cotransplantation of fetal spinal cord and autologous peripheral nerve into the injured cervical spinal cord of the adult rat

In order to compensate the loss of motoneurons resulting from severe spinal cord injury and to reestablish peripheral motor connectivity, solid pieces of fetal spinal cord, taken from embryonic day 14 rat embryos, were transplanted into unilateral aspiration lesions of the cervical spinal cord of adult rats. Concomitantly, one end of a 3.5-cm autologous peripheral nerve graft was put in close contact with the embryonic graft; the other end was sutured to the distal stump of the musculocutaneous nerve which innervate the biceps brachii muscle. The animals were examined 3 and 6 months after surgery. Following intramuscular injection of horseradish peroxidase, retrograde axonal labeling studies indicated that both transplanted and host spinal neurons were able to extend axons all the way through the peripheral nerve graft and nerve stump, up to the reconnected muscles. The labeled cells in the transplant were generally observed close to the intraspinal tip of the peripheral nerve graft. Retrograde axonal tracing, as well as electrophysiological and histological data, demonstrated the sensory and motor reinnervation of the reconnected muscles. This muscular reinnervation was able to reverse the atrophic changes observed in the denervated muscle. In control experiments, the extraspinal end of the peripheral nerve graft was ligatured in order to compare the differentiation of the transplanted neurons and the survival of their growing axons with or without their muscular targets. Six months after both types of surgery, large-size grafted neurons, identified as motoneurons by immunocytochemistry for peripherine and calcitonin gene-related peptide, were only observed in fetal spinal cord transplants which were connected to denervated muscles, thus demonstrating the trophic influence of the muscle target on the survival and differentiation of the transplanted neurons and on the maintenance of the axons they had grown into the peripheral nerve graft.

Tanycytes transplanted into the adult rat spinal cord support the regeneration of lesioned axons

During past years a number of therapeutic strategies have been developed in order to stimulate axonal regeneration after traumatic injuries of the spinal cord. Recently, encouraging data have been obtained by grafting specific glial cells such as Schwann cells or olfactory ensheathing glial cells, known to support the regeneration of peripheral or central axons, respectively. In a recent series of studies, we have shown that tanycytes, a particular glial cell type present in the mediobasal hypothalamus, were able to support the regeneration of a variety of axons innervating this region. The aim of the present study was to determine whether tanycytes could also support the regeneration of lesioned spinal axons. Cultured hypothalamic tanycytes and cortical astrocytes were prelabeled with Fast blue (FB) and grafted into the thoracic spinal cord of adult rats. Three weeks after the transplantation, the animals were fixed and spinal cord sections treated for multiple fluorescence detection of the FB-labeled transplanted cells on the one hand and of various glial and neuronal markers on the other hand. We show here that in all the spinal cords examined, transplanted tanycytes or astrocytes formed large spherical clusters of about 0.5 mm in diameter, located in the mediolateral spinal cord layer. The immunodetection of glial markers showed that transplanted astrocytes exhibited intense immunostaining for both glial fibrillary acidic protein (GFAP) and vimentin (VIM), whereas transplanted tanycytes were intensely immunostained for VIM, but GFAP negative. The immunodetection of axonal markers showed that contrasting with astrocyte transplants, tanycyte transplants were invaded by numerous axonal fibers. These data indicate that tanycyte transplants may represent a useful therapeutic tool for the reparation of the lesioned spinal axons.

Characteristics of human fetal spinal cord grafts in the adult rat spinal cord: influences of lesion and grafting conditions

The present study evaluated the growth potential and differentiation of human fetal spinal cord (FSC) tissue in the injured adult rat spinal cord under different lesion and grafting conditions. Donor tissue at 6-9 weeks of gestational age was obtained through elective abortions and transplanted either immediately into acute resection (solid grafts) or into chronic contusion (suspension and solid grafts) lesions (i.e., 14-40 days after injury) in the thoracic spinal cord. The xenografts were then examined either histologically in plastic sections or immunocytochemically 1-3 months postgrafting. Intraspinal grafts in acute lesions demonstrated an 83% survival rate and developed as well-circumscribed nodules that were predominantly composed of immature astrocytes. Solid-piece grafts in chronic contusion lesions exhibited a 92% survival rate and also developed as nodular masses. These grafts, however, contained many immature neurons 2 months postgrafting. Suspension grafts in chronic contusion lesions had an 85% survival rate and expanded in a nonrestrictive, diffuse pattern. These transplants demonstrated large neuronally rich areas of neural parenchyma. Extensive neuritic outgrowth could also be seen extending from these grafts into the surrounding host spinal cord. These findings show that human FSC tissue reliably survives and differentiates in both acute and chronic lesions. However, both the lesion environment and the grafting techniques can greatly influence the pattern of differentiation and degree of host-graft integration achieved.

Attempts to facilitate dorsal column axonal regeneration in a neonatal spinal environment

The response to injury of ascending collaterals of dorsal root axons within the dorsal column (DC) was studied after neonatal spinal overhemisection (OH) made at different levels of the spinal cord. The transganglionic tracer, cholera toxin conjugated to horseradish peroxidase, and the anterograde tracer, biotinylated dextran amine, were used to label dorsal root ganglion cells with peripheral axons contributing to the sciatic nerve. There was no indication of a regenerative attempt by DC axons at acute survival times (3 days and later) after cervical injury, replicating previous work done at chronic survival periods (Lahr and Stelzner [1990] J. Comp. Neurol. 293:377-398). There was also no evidence of DC regeneration after lumbar OH injury even though immunohistochemical studies using the oligodendrocyte markers Rip and myelin basic protein showed few oligodendrocytes in the gracile fasciculus at lumbar levels at birth. Therefore, the lack of myelin in the dorsal funiculus at lumbar levels does not enhance the growth of neonatally axotomized DC axons. In addition, DC axons did not regenerate when presented with fetal spinal tissue implanted into thoracic OH lesions, even though positive control experiments showed that segmental dorsal root axons containing calcition gene-related peptide and corticospinal axons grew into these implants, replicating previous work of others. When a thoracic OH lesion, with or without a fetal spinal implant, was combined with sciatic nerve injury to attempt to stimulate an intracellular regenerative response of DRG neurons, again, no evidence of DC axonal regeneration was detected. Quantitative studies of the L4 and L5 dorsal root ganglia (DRG) showed that OH injury did not result in DRG neuronal loss. However, sciatic nerve injury did result in significant post-axotomy retrograde cell loss of DRG neurons, even in groups receiving thoracic embryonic spinal implants, and is one explanation for the minimal effect of sciatic nerve injury on DC regeneration. Although fetal tissue did not appear to rescue a significant number of DRG neurons, the quantitative analysis showed an enlargement of the largest class of DRG neuron, the class that contributes to the DC projection, in all groups receiving fetal tissue implants. This apparent trophic effect did not affect DC regeneration or neuronal survival after peripheral axotomy. Further studies are needed to determine why DC axons do not regenerate in a neonatal spinal environment or within fetal tissue implants, especially because previous work by others in both the developing and adult spinal cord shows that dorsal root axons will grow within the same type of fetal spinal implant.

The effect of the platelet derived wound healing formula and the nerve growth factor on the experimentally injured spinal cord

The main purpose of this study is to investigate the effect of platelet derived wound healing formula (PDWHF) and nerve growth factor (NGF) in the treatment of experimental spinal cord injury. PDWHF is a conglomerate of growth factors which include platelet derived growth factor (PDGF), platelet derived angiogenesis factor (PDAF), transforming growth factor-beta (TGF beta) and platelet factor IV (PF4). Complete spinal cord transection was performed at T12 in rats and the treatment of the spinal cord injury was achieved by filling the dead space with type 1 collagen gel impregnated with PDWHF, or with 2.5S-NGF. Controls were treated with only type 1 collagen gel. Animals were sacrificed at 1, 2 or 3 months. Histopathologically, tissue autolysis and cavity formation by phagocytosis expanded 1-3 mm into the cord stumps and the volume of cavitation was less in the two treated groups. In the NGF group, a greater number of surviving nerve cells were observed in this region. Most of the control animals formed only thin, short axonal bundles, however, increased axonal regrowth was noted in animals treated with trophic factors, especially in the NGF group. The NGF group formed thick axonal bundles and abundant neuroma. Increased angiogenesis was observed in the collagen gel matrix and the injured spinal cord parenchyma, in the PDWHF group. Recent studies have shown that mammalian adult CNS possesses the ability for structural and/or functional plasticity following injury under appropriate circumstances. In this in vivo study, exogenous NGF appeared to induce axomal outgrowth and nerve cell survival. PDWHF produced notable angiogenesis which seemed to improve the extracellular microenvironment. This may be important for the delivery of exogenous trophic factors, nutrients and for the changes of extracellular matrices to support nerve cells and axons.

Immunomodulation with intrathymic grafts or anti-lymphocyte serum promotes long-term intraspinal allograft survival

In this study, we sought to test whether introduction of fetal cells into the adult rat thymus would promote immunotolerance to subsequent donor-type allografts in the injured spinal cord. To first evaluate intrathymic survival of fetal central nervous system (CNS) tissue, fragments of E14 Sprague-Dawley (SD) fetal spinal cord (FSCSD) were injected into the thymuses of either adult, outbred SD, or Wistar rats. Histological examination revealed well-differentiated grafts in both the SD (10 out of 13) and Wistar (7 out of 13) recipients. We next examined whether prior intrathymic exposure to FSC graft-derived alloantigens leads to enhanced survival of subsequent allografts into the injured, adult spinal cord. Wistar rats thus first received FSCSD tissue as intrathymic grafts coupled with single-dose, anti-lymphocyte serum (ALS) ablation of the circulating host T-cell population. Ten days later, FCSSD was transplanted into an aspiration lesion of each intrathymic graft recipient's spinal cord. After 60 days, 87% of two-stage graft recipients (n = 15) exhibited viable intraspinal (IS) grafts compared to 38% (3 out of 8) observed in the controls (i.e., not receiving intrathymic grafts). Another group of Wistar rats that had received ALS (only) at the time of the IS FSCSD transplant (n = 8) also had 75% graft survival rates after 60 days. These initial findings show that the intrathymic microenvironment can be a compatible ectopic site for fetal SC graft development and survival. Also, the enhanced survival of intraspinal grafts in animals with previous intrathymic implants or ALS administered at the time of grafting suggests the potential for inducing immunoprotection of some fetal neural allografts in adult recipients.

Immunomodulation with Intrathymic Grafts or Anti-Lymphocyte Serum Promotes Long-Term Intraspinal Allograft Survival

In this study, we sought to test whether introduction of fetal cells into the adult rat thymus would promote immunotolerance to subsequent donor-type allografts in the injured spinal cord. To first evaluate intrathymic survival of fetal central nervous system (CNS) tissue, fragments of E14 Sprague–Dawley (SD) fetal spinal cord (FSC,SD) were injected into the thymuses of either adult, outbred SD, or Wistar rats. Histological examination revealed well-differentiated grafts in both the SD (10 out of 13) and Wistar (7 out of 13) recipients. We next examined whether prior intrathymic exposure to FSC graft-derived alloantigens leads to enhanced survival of subsequent allografts into the injured, adult spinal cord. Wistar rats thus first received FSCSD tissue as intrathymic grafts coupled with single-dose, anti-lymphocyte serum (ALS) ablation of the circulating host T-cell population. Ten days later, FCSSD was transplanted into an aspiration lesion of each intrathymic graft recipient's spinal cord. After 60 days, 87% of two-stage graft recipients (n = 15) exhibited viable intraspinal (IS) grafts compared to 38% (3 out of 8) observed in the controls (i.e., not receiving intrathymic grafts). Another group of Wistar rats that had received ALS (only) at the time of the IS FSCSD transplant (n = 8) also had 75% graft survival rates after 60 days. These initial findings show that the intrathymic microenvironment can be a compatible ectopic site for fetal SC graft development and survival. Also, the enhanced survival of intraspinal grafts in animals with previous intrathymic implants or ALS administered at the time of grafting suggests the potential for inducing immunoprotection of some fetal neural allografts in adult recipients.

Magnetic resonance imaging of the normal and chronically injured adult rat spinal cord in vivo

We assessed the capacity of MRI to show and characterise the spinal cord (SC) in vivo in normal and chronically injured adult rats. In the chronically injured animals the SC was studied by MRI and histological examination. MRI was performed at 1.5 T, using gradient-echo and spin-echo (SE) sequences, the latter with and without gadolinium-DTPA (Gd-DTPA). Several positions were tried for good alignment and to diminish interference by respiratory movements. Images of the SC were obtained in sagittal, coronal, and axial planes. Normal SC was observed as a continuous intensity in both sequences, although contrast resolution was better using SE; it was not possible to differentiate the grey and white matter. Low signal was seen in the damaged area in chronically injured rats, which corresponded to cysts, trabeculae, mononuclear infiltrate, and fibroglial wall on histological examination. Gd-DTPA failed to enhance the SC in normal or chronically injured rats. It did, however, cause enhancement of the lesion after acute SC injury.

Grafting in acute spinal cord injury: morphological and immunological aspects of transplanted adult rat enteric ganglia

We have studied allogeneic transplants of adult rat enteric ganglia in order to evaluate their use as donor tissue for eventual autografts in rodent spinal cord injury models. Female Sprague-Dawley rats of similar weights served either as transplant donors or as recipients. A glass micropipette of 0.8 mm diameter was used to create a local penetrating injury of the lower thoracic spinal cord and the transplant material was pressure injected through the pipette within the neural parenchyma. Ganglia of the myenteric plexus adhering to the stratum longitudinal muscularis were dissected from portions of the jejunum and ileum. Following partial enzymatic digestion and mechanical disruption of the myenteric plexus and muscle tissue (labeled with adherent rhodamine conjugated microbeads), reaggregates of myenteric plexus and muscle were suspended in growth medium and cultured in vitro for one to two days prior to transplantation. Transplants were examined at three, four, six, and eight weeks after surgery. Some of the donor tissue was grown in vitro, in order to determine its cellular composition. These cultured explants were fixed after 10 days, and like myenteric plexus and muscle grafts, were stained histochemically for acetylcholinesterase and observed by fluorescence and light microscopy. At the earlier post-transplantation periods, grafts contained several clusters of enteric ganglion cells that were positive for acetylcholinesterase and exhibited ultrastructural features characteristic of the enteric nervous system. They had well-defined boundaries. Reactive astrocytes and their processes remained located within the host spinal cord adjacent to the boundary region of the grafts. Likewise, macrophages were located in areas abutting the graft. Newly formed vasculature penetrated the graft interior and appeared to be continuous with the host vessels. Grafts grown for at least eight weeks were characterized by interdigitating boundaries. Finger-like protrusions of graft tissue containing fibroblasts and collagen intermixed with adjacent gray and white matter of the host cord. Such transplants also had reactive astrocytes and ED1-positive macrophages. At this later stage, several groups of ganglion cells were identified that were intensely acetylcholinesterase-positive; however, only two of four grafts were recovered, whereas two of the transplants degenerated. We postulate that degeneration of allogeneic grafts may occur as a result of ongoing immune responses of the host which could be prevented by use of autogeneic enteric ganglia. Our studies show that fully differentiated enteric ganglia can survive transplantation to acutely injured spinal cord of adult rats.

Fetal grafts alter chronic behavioral outcome after contusion damage to the adult rat spinal cord

In the present experiments, we have examined the capacity of intraspinal transplants to effect alterations in certain locomotor behaviors after spinal contusion injuries. An electromechanical impactor that was sensitive to tissue biomechanical characteristics was used to produce rapid (20 ms) compression injuries to the thoracic spinal cord (T8). Suspensions of fetal spinal tissue (14-day) were placed at 10 days postinjury into the intraspinal cavity created by these reproducible spinal injuries. In the pre- and postinjury period, a number of general and sensitive motor behaviors were used to characterize the immediate and long-term progress of hindlimb behavioral recovery over an extended period of time (73 days). Our data reveal that a lasting alteration in some motor behaviors can be achieved by suspension grafts. While little improvement in some generalized motor tasks (inclined plane analysis, grid walking) takes place, fetal transplants precipitate a rapid and enduring change in certain motivated fine motor behaviors (gait analysis). The base of support and stride length of the hindlimbs were improved by 7 days post-transplantation and the effect was stable over time. The angle of rotation was, however, not altered. The lasting effect in two gait parameters noted was accompanied by the presence of well-developed spinal grafts that often fused with the host spinal parenchyma. These results provide the first documentation of an influence of fetal transplants on motivated locomotor capacity in a well-characterized spinal injury model that mimics lesions seen in the contused adult human spinal cord.

The effect of growth factor formula (platelet derived wound healing formula) in experimental spinal cord injuries

The main purpose of this study was to investigate the usefulness of platelet derived wound healing formula (PDWHF) in the treatment of experimentally induced spinal cord injuries in cats. The injury model in ten adult cats consisted of the placement of three 22-gauge Teflon catheter sheaths into the spinal cord at the L2 level. Treatment consisted of coating these sheaths with PDWHF in Hydron. Three animals were used as controls. In the 7 remaining cats, treatment was double blinded. Cats were sacrificed at 3 weeks after injury and injured spinal cord segments were excised for histologic evaluation. Electrophysiologic and clinical motor function were evaluated throughout a period of observation. Evoked potentials in both the treated and control groups indicated incomplete spinal cord lesions due to insertion of the needles. There did not appear to be any significant improvement or difference in the evoked response and clinical function as a result of treatment with PDWHF. The histological findings in the PDWHF-treated group showed significant new vessel formation as well as dilation and around the injury site. This neovascularization, both qualitative and quantitative, was noted in the treatment group. This information, with a limited injury and very simple delivery system for growth factor, would suggest there is definite neovascularization occurring as a result of this treatment and this may be useful in the subsequent wound healing response such as axonal growth and scar tissue formation.

Axonal projections between fetal spinal cord transplants and the adult rat spinal cord: a neuroanatomical tracing study of local interactions

Three neuroanatomical tracers have been employed to map the axonal projections formed between transplants of fetal spinal cord tissue and the surrounding host spinal cord in adult rats. Solid pieces of embryonic day 14 (E14) rat spinal cord were placed into hemisection aspiration cavities in the lumbar spinal cord. Injections of either (1) a mixture of horseradish peroxidase and wheat germ agglutinin- conjugated horseradish peroxidase, (2) Fluoro-Gold, or (3) Phaseolus vulgaris leucoagglutinin (PHA-L) were made into the transplants or the neighboring segments of the host spinal cord at 6 weeks to 14 months post-transplantation. Injections of anterograde and retrograde tracers into the transplants revealed extensive intrinsic projections that often spanned the length of the grafts. Axons arising from the transplants extended into the host spinal cord as far as 5 mm from the host-graft interface, as best revealed by retrograde labeling with Fluoro-Gold. Consistent with these observations, iontophoretic injections of PHA-L into the transplants also produced labeled axonal profiles at comparable distances in the host spinal cord, and in some instances elaborate terminals fields were observed surrounding host neurons. The majority of these efferent fibers labeled with PHA-L, however, were confined to the immediate vicinity of the host-graft boundary, and no fibers were seen traversing cellular partitions between host and transplant tissues. Host afferents to the transplants were also revealed by these tracing methods. For example, the injection of Fluoro-Gold into the grafts resulted in labeling of host neurons within the spinal cord and nearby dorsal root ganglia. In most cases, retrogradely labeled neurons in spinal gray matter were located within 0.5 mm of the graft site, although some were seen as far as 4-6 mm away. The distance and relative density of ingrowth exhibited by host axons into the grafts, however, appeared modest based upon the results of HRP and Fluoro-Gold retrograde labeling. This was further confirmed with the PHA-L anterograde method. Whereas some host fibers were seen extending into the transplants, the majority of PHA-L containing axons formed terminal-like profiles at or within 0.5 mm of the host-graft interface. The comprehensive view of intrinsic connectivity and host-graft projections obtained in these studies indicates that intraspinal grafts of fetal spinal cord tissue can establish a short-range intersegmental circuitry in the injured, adult spinal cord. These observations are consistent with the view that such grafts may contribute to the formation of a functional relay between separated segments of the spinal cord after injury.(ABSTRACT TRUNCATED AT 400 WORDS)

Oxygen transport in intraspinal fetal grafts: graft-host relations

In the present experiments, we determined tissue oxygen tension (PtO2) levels within the injured spinal cords of adult rats following transplantation of fetal spinal cord tissue. Partial resection cavities were made at L1-L2 levels after which whole pieces of 14-day donor tissue were placed into the cavities. Analysis of recordings obtained from graft tissues at 1 and 2 months after transplantation revealed low PtO2 values in many cases. Even the more extensively developed transplants at 3 months continued to show mean PtO2 levels lower than those taken from normal, mature spinal cord tissue. Measurements from host tissue, adjacent to a lesion in which no graft was introduced, showed normal or elevated PtO2 levels. In contrast, where extensive host and graft integration had occurred, the PtO2 levels of adjacent host resembled those obtained within the transplants. On the other hand, in cases of poor host-graft integration, characterized by either cellular or fibrotic graft-host interfaces or large cysts, the PtO2 tensions exceeded normal levels. Therefore, the present results show that when fetal grafts are placed acutely into an aspiration cavity within the adult spinal cord, the transplants quickly establish an oxygen microenvironment resembling that found during normal fetal development. Oxygen transport is therefore a regulated variable in the graft neuropil as it is in the normally developing spinal cord. Furthermore, in the presence of closely approximated fetal transplants, adjacent host tissue assumes tissue oxygen levels that mimic those in the graft. This "inductive" effect gradually diminishes as development proceeds and may be the hallmark of successful graft-host integration.

Regeneration of adult dorsal root axons into transplants of fetal spinal cord and brain: a comparison of growth and synapse formation in appropriate and inappropriate targets

Cut dorsal root axons regenerate into transplants of embryonic spinal cord and form synapses that resemble those found in the dorsal horn of normal spinal cord. One aim of the present study was to determine whether these axons also regenerate into and establish synapses within transplants of embryonic brain. A second aim was to compare the patterns of growth in embryonic brain and spinal cord transplants. Embryonic spinal cord or brain was transplanted into the lumbar enlargement of adult Sprague-Dawley rats, the L4 or L5 dorsal root was cut, and the cut root was juxtaposed to the transplant. The transplants included whole pieces or dissociated cell suspensions of embryonic day 14 (E14) spinal cord, or whole pieces of E14 neocortex, E18 occipital cortex, E15 cerebellum, or E18 hippocampus. One month later the regenerated dorsal root axons were labeled by immunocytochemical methods to demonstrate calcitonin gene-related peptide (CGRP). CGRP-immunoreactive axons regenerated into all the transplants examined and formed synapses in the neocortex and cerebellum transplants in which they were sought. Synapses were far rarer in neocortex and cerebellum than we had observed previously in transplanted spinal cord, and the patterns of growth differed in transplants of spinal cord and brain. In solid transplants of spinal cord, regenerated axons remained relatively close to the interface with the dorsal root, branched, and formed bundles. Areas of dense ingrowth were separated by regions with few labeled axons. In transplants of brain regions, the regenerated axons were few, unbranched, and appeared as individual fibers rather than in bundles, but they were distributed widely in neocortex transplants. The results of quantitative studies confirmed these observations. The area fraction occupied by regenerated axons in solid spinal cord transplants was significantly larger than in occipital cortex or cerebellum transplants. Distribution histograms of the area occupied in transplants demonstrated that regenerated axons were distributed sparsely but homogeneously in transplants of brain, whereas spinal cord transplants were heterogeneous for regenerated axons and contained areas in which growth was dense or sparse. In contrast, several measurements of axon distribution, including area, longest axis, and length of lateral extension, indicated that CGRP-labeled axons spread more widely in occipital cortex transplants than in solid transplants of spinal cord or cerebellum. The results indicate that embryonic CNS tissues that are not normal targets support or enhance the growth of severed dorsal roots and suggest that the conditions that constitute a permissive environment for regenerating axons are relatively nonspecific.(ABSTRACT TRUNCATED AT 400 WORDS)

The response of the cerebral hemisphere of the rat to injury. II. The neonatal rat

The response to injury of the cerebrum of the neonatal rat was studied in knife wounds by using both light and electron microscopical, and immunohistochemical, techniques. The rats were injured at 2, 4, 8, 12, 16 and 20 dayspost natumand the tissues examined 8 days later. A mature scar, that is, a layer of fibrous tissue separated from the injured neuropile by a glia limitans, is not formed in the brains of rats lesioned before 8 dayspost natum. Before this time, the neuropile of the severed hemisphere grows together and both the glia limitans externa and ventricular lining are repaired. The only evidence of the wound, 20 days after injury, is a subpial and periventricular accumulation of astrocytes and occasional groups of blood vessels; elsewhere glial and neuronal processes traverse the wound obliterating all signs of the original lesion. After 8 dayspost natum, scar tissue is deposited. The scar first appears in the superficial cortex as fibroblasts and macrophages invade from the meninges. With increasing age at injury, these cells penetrate more deeply and, after 16 dayspost natumat injury, the entire lesion contains these cells. Concomitantly, a glia limitans is formed over the walls of the lesion, firstly in the superficial cortex continuous with the glia limitans externa, and successively in the deeper cortex, white matter and corpus striatum as the meningeal fibroblasts and macrophages invade these regions. In the developing cerebrum, injured before 8 dayspost natum, the failure to form a scar is unrelated to the maturity of the astrocytes and fibroblasts, because both interact to regenerate the glia limitans externa. The development of a scar, in animals injured after 8 dayspost natum, is correlated with the failure of both axonal and dendritic regeneration. Because there are few oligodendrocytes, and no myelin, it appears that inhibition of axonal and dendritic growth is linked to scar formation, and not to putative inhibitory substrates such as those on the surface of oligodendrocytes, CNS scarring may be initiated by the invasion of fibroblasts and macrophages from the meninges into the injured neuropile. The possible reasons why these mesenchymal cells fail to penetrate before 8 dayspost natumare discussed.

Changes in astroglial scar formation in rat optic nerve as a function of development

Although astroglial scar formation is a common response to almost any type of injury to the adult central nervous system, lesions in fetal and neonatal rats have been reported to induce little or no scar formation. To examine this developmental difference further, rats ranging in age from 1 to 65 days postnatal were unilaterally enucleated, a surgical procedure that causes the axons in the optic nerve to degenerate. The optic nerves were processed for light and electron microscopy at times ranging from 7 to 365 days postenucleation. Pronounced and permanent glial scars were formed in every age group examined, including the neonates. However, the time course for removal of the degenerating axonal debris and formation of a compact, debris-free glial scar varied as a function of developmental age. In neonatal rats, a compact glial scar formed in 1-2 weeks whereas 3-5 months were required for compact glial scar formation in juveniles and adults. Changes in cross-sectional area were also associated with optic nerve degeneration and glial scar formation. Whereas lesioned neonatal optic nerves underwent little change in area, there was a substantial decrease in area in the juvenile and adult. Morphometric analysis showed that irrespective of the age of the animal at the time of enucleation, the final area of the compact glial scar was 10-20% of the unlesioned adult control. These results suggest that conflict in the literature over the ability of neonatal astrocytes to form a glial scar may be due to the nature of the lesion or the method of detection since astrocytes in the neonatal rat optic nerve clearly have the capacity to become reactive and form a glial scar.

Evaluation of blood vessel and neurite growth into a collagen matrix placed within a surgically created gap in rat spinal cord

A complete gap of 3-4 mm was surgically created in the spinal cord of adult rats between the T8-T10 vertebral level, filled with a collagen matrix and closed with sutures. Animals were killed at weekly intervals from 14 to 42 days postimplantation. The collagen implant (CI) was evaluated for ingrowth of blood vessels and neurites using light and electron microscopic techniques. At 42 days postimplantation, 3 CI animals underwent a transection at the rostro-caudal center of the CI followed by placement of horseradish peroxidase (HRP)-impregnated filter paper between the cut ends. The number and location of HRP-labeled cells in CI animals were compared to normal animals that received a spinal cord transection at the T9 vertebral level immediately followed by placement of HRP between the cut stumps of spinal cord. Connective tissue (CT) septae, neurites and blood vessels invaded the CI from adjacent spinal neuropil and surrounding CT capsule. CI animals revealed HRP-labeled cells in the intermediolateral cell column (IML), parabrachial nuclei, locus coeruleus and red nucleus with a preponderance of labeled cells found in the IML rostral to the CI. In contrast, no IML were labeled in thoracic spinal cord rostral to HRP implantation in control animals. It was concluded that the above brainstem nuclei, which normally project axons into spinal cord, are capable of extending their severed axons into the CI following spinal cord injury and that uninjured IML cells also sprout axons into the CI.

Implantation of cultured sensory neurons and Schwann cells into lesioned neonatal rat spinal cord. I. Methods for preparing implants from dissociated cells

Our goal was to devise methods of implanting defined populations of the cellular constituents of peripheral nerve into regions of spinal cord injury. This objective derived from the knowledge that the cellular environment of peripheral nerve is known to be supportive of axon regeneration from both central and peripheral neurons. Two of the constituents of the peripheral nerve environment known to influence axonal growth are the Schwann cell and extracellular matrix (particularly basal lamina), both of which can be obtained in culture. We describe here large-scale methods of establishing purified populations of rat sensory neurons to which purified populations of Schwann cells were added. These essentially monolayer preparations were then scrolled and cut into lengths of proper shape and size to provide implants for sites of spinal cord injury in newborn rats. We also describe methods enabling the addition of leptomeningeal components to the implants; this addition contributes a proliferating population of vascular endothelial cells (identified by immunostaining) to the otherwise vasculature-free neuron/Schwann cell implant. Light and electron microscopic observations were made to characterize the implants. When the implant was ready for use, it contained Schwann cells that were differentiated, i.e., had begun to ensheathe axons and form basal lamina. The use of a medium containing human plasma to foster endothelial cell growth led to increased neurite fasciculation and Schwann cell migratory activity in the outgrowth, particularly when the neurons and Schwann cells were cultured on leptomeninges. The second paper in this series reports the deportment of these implants and their influence on corticospinal tract growth after placement into regions of dorsal column injury in neonatal rats (Kuhlengel et al., J. Comp. Neurol 293:74-91, 1990).

Ultrastructural organization of regenerated adult dorsal root axons within transplants of fetal spinal cord

It has previously been demonstrated that the severed central branches of adult mammalian dorsal root ganglion cells regenerate into transplants of fetal spinal cord. The aim of this study was to determine whether these regenerating axons form synapses, and, if they do, to characterize them morphologically. Embryonic day 14 or 15 spinal cord was transplanted into the lumbar enlargement of adult Sprague-Dawley rats, and the L4 or L5 dorsal root was cut and then juxtaposed to the transplant. One to 3 months later the regenerated dorsal roots were labeled by anterograde filling with wheat germ agglutinin-horseradish peroxidase (WGA-HRP) or by immunocytochemistry for calcitonin gene-related peptide (CGRP). Dorsal root labeling with WGA-HRP demonstrated that regenerated axon terminals made synaptic contacts within transplants, and stereological electron microscopic analysis demonstrated that CGRP-immunoreactive axon terminals occupied an average of 9% of the neuropil within 2 mm of the dorsal root-transplant interface. The majority of synapses were axodendritic, but a significant percentage were axosomatic or axoaxonic. Since axoaxonic synapses were observed in transplants in which both pre- and postsynaptic profiles of axoaxonic synapses were labeled for CGRP, some regenerated axons apparently form synapses with each other. Approximately 90% of synaptic contacts were simple, 9% were complex, and 25% of the complex terminals were immunopositive for CGRP. Glia occupied 25% of the neuropil within 1 mm of the dorsal root-transplant interface, but only 6% of the neuropil 1-2 mm from the interface. We also performed a stereological analysis of the neuropil in lamina I. The area fractions of neuropil occupied by myelinated axons, perikarya, and dendrites were similar in transplants and in lamina I. However, the area fraction occupied by unmyelinated axons was significantly smaller in transplants, and the area fraction occupied by axon terminals was significantly larger in transplants compared with lamina I. Regenerated CGRP-immunoreactive synaptic terminals in transplants were significantly larger than in normal lamina I, and their synaptic contact length was also increased, suggesting that a compensatory mechanism for increasing synaptic efficiency might occur within the transplants. Synaptic density, however, was significantly reduced in transplants, indicating a smaller number of synaptic terminals per unit area. In lamina I, as in the transplant, most synapses were axodendritic, but the percentage of axosomatic and axoaxonic terminals was lower in lamina I than in the transplants.(ABSTRACT TRUNCATED AT 400 WORDS)

Transplantation of cultured embryonic spinal cord grafts into the hemisected spinal cord of adult rabbits

Spinal cord fragments from 20-day-old rabbit embryos cultivated for 1 week were transplanted into the hemisected and intact spinal cord of adult rabbits. The morphological changes at the site of intervention were investigated by light and electron microscopy 3, 12, and 29 weeks following implantation. In 80% of the animals the procedure was successful. The implants grew in volume, the cells matured, and many new neural processes with myelinization and synapse formation appeared. The histological findings indicate the survival, maturation, and integration of transplanted cultured embryonic spinal cord tissue in the lesioned adult spinal cord.