Olfactory ensheathing cells reduce duration of autonomic dysreflexia in rats with high spinal cord injury

Glia in tissue engineering: From biomaterial tools to transplantation

Glia are imperative in nearly every function of the nervous system, including neurotransmission, neuronal repair, development, immunity, and myelination. Recently, the reparative roles of glia in the central and peripheral nervous systems have been elucidated, suggesting a tremendous potential for these cells as novel treatments to central nervous system disorders. Glial cells often behave as 'double-edged swords' in neuroinflammation, ultimately deciding the life or death of resident cells. Compared to glia, neuronal cells have limited mobility, lack the ability to divide and self-renew, and are generally more delicate. Glia have been candidates for therapeutic use in many successful grafting studies, which have been largely focused on restoring myelin with Schwann cells, olfactory ensheathing glia, and oligodendrocytes with support from astrocytes. However, few therapeutics of this class have succeeded past clinical trials. Several tools and materials are being developed to understand and re-engineer these grafting concepts for greater success, such as extra cellular matrix-based scaffolds, bioactive peptides, biomolecular delivery systems, biomolecular discovery for neuroinflammatory mediation, composite microstructures such as artificial channels for cell trafficking, and graft enhanced electrical stimulation. Furthermore, advances in stem cell-derived cortical/cerebral organoid differentiation protocols have allowed for the generation of patient-derived glia comparable to those acquired from tissues requiring highly invasive procedures or are otherwise inaccessible. However, research on bioengineered tools that manipulate glial cells is nowhere near as comprehensive as that for systems of neurons and neural stem cells. This article explores the therapeutic potential of glia in transplantation with an emphasis on novel bioengineered tools for enhancement of their reparative properties. STATEMENT OF SIGNIFICANCE: Neural glia are responsible for a host of developmental, homeostatic, and reparative roles in the central nervous system but are often a major cause of tissue damage and cellular loss in insults and degenerative pathologies. Most glial grafts have employed Schwann cells for remyelination, but other glial with novel biomaterials have been employed, emphasizing their diverse functionality. Promising strategies have emerged, including neuroimmune mediation of glial scar tissues and facilitated migration and differentiation of stem cells for neural replacement. Herein, a comprehensive review of biomaterial tools for glia in transplantation is presented, highlighting Schwann cells, astrocytes, olfactory ensheating glia, oligodendrocytes, microglia, and ependymal cells.

Autonomic Dysreflexia in Spinal Cord Injury: Mechanisms and Prospective Therapeutic Targets

High-level spinal cord injury (SCI) often results in cardiovascular dysfunction, especially the development of autonomic dysreflexia. This disorder, characterized as an episode of hypertension accompanied by bradycardia in response to visceral or somatic stimuli, causes substantial discomfort and potentially life-threatening symptoms. The neural mechanisms underlying this dysautonomia include a loss of supraspinal control to spinal sympathetic neurons, maladaptive plasticity of sensory inputs and propriospinal interneurons, and excessive discharge of sympathetic preganglionic neurons. While neural control of cardiovascular function is largely disrupted after SCI, the renin-angiotensin system (RAS), which mediates blood pressure through hormonal mechanisms, is up-regulated after injury. Whether the RAS engages in autonomic dysreflexia, however, is still controversial. Regarding therapeutics, transplantation of embryonic presympathetic neurons, collected from the brainstem or more specific raphe regions, into the injured spinal cord may reestablish supraspinal regulation of sympathetic activity for cardiovascular improvement. This treatment reduces the occurrence of spontaneous autonomic dysreflexia and the severity of artificially triggered dysreflexic responses in rodent SCI models. Though transplanting early-stage neurons improves neural regulation of blood pressure, hormonal regulation remains high and baroreflex dysfunction persists. Therefore, cell transplantation combined with selected RAS inhibition may enhance neuroendocrine homeostasis for cardiovascular recovery after SCI.

Considering the Cellular Composition of Olfactory Ensheathing Cell Transplants for Spinal Cord Injury Repair: A Review of the Literature

Olfactory ensheathing cells (OECs) are specialized glia cells of the olfactory system that support the continual regeneration of olfactory neurons throughout adulthood. Owing to their pro-regenerative properties, OECs have been transplanted in animal models of spinal cord injuries (SCI) and trialed in clinical studies on SCI patients. Although these studies have provided convincing evidence to support the continued development of OEC transplantation as a treatment option for the repair of SCI, discrepancies in the reported outcome has shown that OEC transplantation requires further improvement. Much of the variability in the reparative potential of OEC transplants is due to the variations in the cell composition of transplants between studies. As a result, the optimal cell preparation is currently a subject of debate. Here we review, the characterization as well as the effect of the cell composition of olfactory cell transplantation on therapeutic outcome in SCI. Firstly, we summarize and review the cell composition of olfactory cell preparations across the different species studied prior to transplantation. Since the purity of cells in olfactory transplants might affect the study outcome we also examine the effect of the proportions of OECs and the different cell types identified in the transplant on neuroregeneration. Finally, we consider the effect of the yield of cells on neuroregeneration by assessing the cell dose of transplants on therapeutic outcome.

Optimizing Olfactory Ensheathing Cell Transplantation for Spinal Cord Injury Repair

Cell transplantation constitutes an important avenue for development of new treatments for spinal cord injury (SCI). These therapies are aimed at supporting neural repair and/or replacing lost cells at the injury site. To date, various cell types have been trialed, with most studies focusing on different types of stem cells or glial cells. Here, we review commonly used cell transplantation approaches for spinal cord injury (SCI) repair, with focus on transplantation of olfactory ensheathing cells (OECs), the glial cells of the primary olfactory nervous system. OECs are promising candidates for promotion of neural repair given that they support continuous regeneration of the olfactory nerve that occurs throughout life. Further, OECs can be accessed from the nasal mucosa (olfactory neuroepithelium) at the roof of the nasal cavity and can be autologously transplanted. OEC transplantation has been trialed in many animal models of SCI, as well as in human clinical trials. While several studies have been promising, outcomes are variable and the method needs improvement to enhance aspects such as cell survival, integration, and migration. As a case study, we include the approaches used by our team (the Clem Jones Centre for Neurobiology and Stem Cell Research, Griffith University, Nathan, QLD, Australia) to address the current problems with OEC transplantation and discuss how the therapeutic potential of OEC transplantation can be improved. Our approach includes discovery research to improve our knowledge of OEC biology, identifying natural and synthetic compounds to stimulate the neural repair properties of OECs, and designing three-dimensional cell constructs to create stable and transplantable cell structures.

Reliable cell purification and determination of cell purity: crucial aspects of olfactory ensheathing cell transplantation for spinal cord repair

Transplantation of olfactory ensheathing cells, the glia of the primary olfactory nervous system, has been trialed for spinal cord injury repair with promising but variable outcomes in animals and humans. Olfactory ensheathing cells can be harvested either from the lamina propria beneath the neuroepithelium in the nasal cavity, or from the olfactory bulb in the brain. As these areas contain several other cell types, isolating and purifying olfactory ensheathing cells is a critical part of the process. It is largely unknown how contaminating cells such as fibroblasts, other glial cell types and supporting cells affect olfactory ensheathing cell function post-transplantation; these cells may also cause unwanted side-effects. It is also, however, possible that the presence of some of the contaminant cells can improve outcomes. Here, we reviewed the last decade of olfactory ensheathing cell transplantation studies in rodents, with a focus on olfactory ensheathing cell purity. We analyzed how purification methods and resultant cell purity differed between olfactory mucosa- and olfactory bulb-derived cell preparations. We analyzed how the studies reported on olfactory ensheathing cell purity and which criteria were used to define cells as olfactory ensheathing cells. Finally, we analyzed the correlation between cell purity and transplantation outcomes. We found that olfactory bulb-derived olfactory ensheathing cell preparations are typically purer than mucosa-derived preparations. We concluded that there is an association between high olfactory ensheathing cell purity and favourable outcomes, but the lack of olfactory ensheathing cell-specific markers severely hampers the field.

Survival and Integration of Transplanted Olfactory Ensheathing Cells are Crucial for Spinal Cord Injury Repair: Insights from the Last 10 Years of Animal Model Studies

Olfactory ensheathing cells (OECs), the glial cells of the primary olfactory nervous system, support the natural regeneration of the olfactory nerve that occurs throughout life. OECs thus exhibit unique properties supporting neuronal survival and growth. Transplantation of OECs is emerging as a promising treatment for spinal cord injury; however, outcomes in both animals and humans are variable and the method needs improvement and standardization. A major reason for the discrepancy in functional outcomes is the variability in survival and integration of the transplanted cells, key factors for successful spinal cord regeneration. Here, we review the outcomes of OEC transplantation in rodent models over the last 10 years, with a focus on survival and integration of the transplanted cells. We identify the key factors influencing OEC survival: injury type, source of transplanted cells, co-transplantation with other cell types, number and concentration of cells, method of delivery, and time of transplantation after the injury. We found that two key issues are hampering optimization and standardization of OEC transplantation: lack of (1) reliable methods for identifying transplanted cells, and (2) three-dimensional systems for OEC delivery. To develop OEC transplantation as a successful and standardized therapy for spinal cord injury, we must address these issues and increase our understanding of the complex parameters influencing OEC survival.

Why are olfactory ensheathing cell tumors so rare?

The glial cells of the primary olfactory nervous system, olfactory ensheathing cells (OECs), are unusual in that they rarely form tumors. Only 11 cases, all of which were benign, have been reported to date. In fact, the existence of OEC tumors has been debated as the tumors closely resemble schwannomas (Schwann cell tumors), and there is no definite method for distinguishing the two tumor types. OEC transplantation is a promising therapeutic approach for nervous system injuries, and the fact that OECs are not prone to tumorigenesis is therefore vital. However, why OECs are so resistant to neoplastic transformation remains unknown. The primary olfactory nervous system is a highly dynamic region which continuously undergoes regeneration and neurogenesis throughout life. OECs have key roles in this process, providing structural and neurotrophic support as well as phagocytosing the axonal debris resulting from turnover of neurons. The olfactory mucosa and underlying tissue is also frequently exposed to infectious agents, and OECs have key innate immune roles preventing microbes from invading the central nervous system. It is possible that the unique biological functions of OECs, as well as the dynamic nature of the primary olfactory nervous system, relate to the low incidence of OEC tumors. Here, we summarize the known case reports of OEC tumors, discuss the difficulties of correctly diagnosing them, and examine the possible reasons for their rare incidence. Understanding why OECs rarely form tumors may open avenues for new strategies to combat tumorigenesis in other regions of the nervous system.

Autonomic dysreflexia: a cardiovascular disorder following spinal cord injury

Autonomic dysreflexia (AD) is a serious cardiovascular disorder in patients with spinal cord injury (SCI). The primary underlying cause of AD is loss of supraspinal control over sympathetic preganglionic neurons (SPNs) caudal to the injury, which renders the SPNs hyper-responsive to stimulation. Central maladaptive plasticity, including C-fiber sprouting and propriospinal fiber proliferation exaggerates noxious afferent transmission to the SPNs, causing them to release massive sympathetic discharges that result in severe hypertensive episodes. In parallel, upregulated peripheral vascular sensitivity following SCI exacerbates the hypertensive response by augmenting gastric and pelvic vasoconstriction. Currently, the majority of clinically employed treatments for AD involve anti-hypertensive medications and Botox injections to the bladder. Although these approaches mitigate the severity of AD, they only yield transient effects and target the effector organs, rather than addressing the primary issue of central sympathetic dysregulation. As such, strategies that aim to restore supraspinal reinnervation of SPNs to improve cardiovascular sympathetic regulation are likely more effective for AD. Recent pre-clinical investigations show that cell transplantation therapy is efficacious in reestablishing spinal sympathetic connections and improving hemodynamic performance, which holds promise as a potential therapeutic approach.

High nasal resistance is stable over time but poorly perceived in people with tetraplegia and obstructive sleep apnoea

Obstructive sleep apnoea (OSA) is highly prevalent in people with tetraplegia. Nasal congestion, a risk factor for OSA, is common in people with tetraplegia. The purpose of this study was to quantify objective and perceived nasal resistance and its stability over four separate days in people with tetraplegia and OSA (n=8) compared to able-bodied controls (n=6). Awake nasal resistance was quantified using gold standard choanal pressure recordings (days 1 and 4) and anterior rhinomanometry (all visits). Nasal resistance (choanal pressure) was higher in people with tetraplegia versus controls (5.3[6.5] vs. 2.1[2.4] cmH₂O/L/s, p=0.02) yet perceived nasal congestion (modified Borg score) was similar (0.5[1.8] vs. 0.5[2.0], p=0.8). Nasal resistance was stable over time in both groups (CV=0.23±0.09 vs. 0.16±0.08, p=0.2). These findings are consistent with autonomic dysfunction in tetraplegia and adaptation of perception to high nasal resistance. Nasal resistance may be an important therapeutic target for OSA in this population but self-assessment cannot reliably identify those most at risk.

Olfactory ensheathing cells but not fibroblasts reduce the duration of autonomic dysreflexia in spinal cord injured rats

Autonomic dysreflexia is a common complication after high level spinal cord injury and can be life-threatening. We have previously shown that the acute transplantation of olfactory ensheathing cells into the lesion site of rats transected at the fourth thoracic spinal cord level reduced autonomic dysreflexia up to 8weeks after spinal cord injury. This beneficial effect was correlated with changes in the morphology of sympathetic preganglionic neurons despite the olfactory cells surviving no longer than 3weeks. Thus the transitory presence of olfactory ensheathing cells at the injury site initiated long-term functional as well as morphological changes in the sympathetic preganglionic neurons. The primary aim of the present study was to evaluate whether olfactory ensheathing cells survive after transplantation within the parenchyma close to sympathetic preganglionic neurons and whether, in this position, they still reduce the duration of autonomic dysreflexia and modulate sympathetic preganglionic neuron morphology. The second aim was to quantify the density of synapses on the somata of sympathetic preganglionic neurons with the hypothesis that the reduction of autonomic dysreflexia requires synaptic changes. As a third aim, we evaluated the cell type-specificity of olfactory ensheathing cells by comparing their effects with a control group transplanted with fibroblasts. Animals transplanted with OECs had a faster recovery from hypertension induced by colorectal distension at 6 and 7weeks but not at 8weeks after T4 spinal cord transection. Olfactory ensheathing cells survived for at least 8weeks and were observed adjacent to sympathetic preganglionic neurons whose overall number of primary dendrites was reduced and the synaptic density on the somata increased, both caudal to the lesion site. Our results showed a long term cell type-specific effects of olfactory ensheathing cells on sympathetic preganglionic neurons morphology and on the synaptic density on their somata, and a transient cell type-specific reduction of autonomic dysreflexia.

Cardiovascular dysfunction following spinal cord injury

Both sensorimotor and autonomic dysfunctions often occur after spinal cord injury (SCI). Particularly, a high thoracic or cervical SCI interrupts supraspinal vasomotor pathways and results in disordered hemodynamics due to deregulated sympathetic outflow. As a result of the reduced sympathetic activity, patients with SCI may experience hypotension, cardiac dysrhythmias, and hypothermia post-injury. In the chronic phase, changes within the CNS and blood vessels lead to orthostatic hypotension and life-threatening autonomic dysreflexia (AD). AD is characterized by an episodic, massive sympathetic discharge that causes severe hypertension associated with bradycardia. The syndrome is often triggered by unpleasant visceral or sensory stimuli below the injury level. Currently the only treatments are palliative - once a stimulus elicits AD, pharmacological vasodilators are administered to help reduce the spike in arterial blood pressure. However, a more effective means would be to mitigate AD development by attenuating contributing mechanisms, such as the reorganization of intraspinal circuits below the level of injury. A better understanding of the neuropathophysiology underlying cardiovascular dysfunction after SCI is essential to better develop novel therapeutic approaches to restore hemodynamic performance.

Contemporary Cardiovascular Concerns after Spinal Cord Injury: Mechanisms, Maladaptations, and Management

Cardiovascular (CV) issues after spinal cord injury (SCI) are of paramount importance considering they are the leading cause of death in this population. Disruption of autonomic pathways leads to a highly unstable CV system, with impaired blood pressure (BP) and heart rate regulation. In addition to low resting BP, on a daily basis the majority of those with SCI suffer from transient episodes of aberrantly low and high BP (termed orthostatic hypotension and autonomic dysreflexia, respectively). In fact, autonomic issues, including resolution of autonomic dysreflexia, are frequently ranked by individuals with high-level SCI to be of greater priority than walking again. Owing to a combination of these autonomic disturbances and a myriad of lifestyle factors, the pernicious process of CV disease is accelerated post-SCI. Unfortunately, these secondary consequences of SCI are only beginning to receive appropriate clinical attention. Immediately after high-level SCI, major CV abnormalities present in the form of neurogenic shock. After subsiding, new issues related to BP instability arise, including orthostatic hypotension and autonomic dysreflexia. This review describes autonomic control over the CV system before injury and the mechanisms underlying CV abnormalities post-SCI, while also detailing the end-organ consequences, including those of the heart, as well as the systemic and cerebral vasculature. The tertiary impact of CV dysfunction will also be discussed, such as the potential impediment of rehabilitation, and impaired cognitive function. In the recent past, our understanding of autonomic dysfunctions post-SCI has been greatly enhanced; however, it is vital to further develop our understanding of the long-term consequences of these conditions, which will equip us to better manage CV disease morbidity and mortality in this population.

Neuroprotection, Plasticity Manipulation, and Regenerative Strategies to Improve Cardiovascular Function following Spinal Cord Injury

Damage to the central nervous system, as in the case of spinal cord injury (SCI), results in disrupted supraspinal sympathetic influence and subsequent cardiovascular control impairments. Consequently, people with SCI suffer from disordered basal hemodynamics and devastating fluctuations in blood pressure, as in the case of autonomic dysreflexia (AD), which likely contribute to this population's leading cause of mortality: cardiovascular disease. The development of AD is related, at least in part, to neuroanatomical changes that include disrupted descending supraspinal sympathetic control, changes in propriospinal circuitry, and inappropriate afferent sprouting in the dorsal horn. These anatomical mechanisms may thus be targeted by neural regenerative and protective therapies to improve cardiovascular control and reduce AD. Here, we discuss the relationship between abnormal cardiovascular control and its underlying neuroanatomy. We then review current studies investigating biochemical strategies to reduce the severity of AD through: 1) reducing aberrant calcitonin gene-related peptide immunoreactive afferent sprouting; 2) inhibiting inflammatory processes; and 3) re-establishing descending supraspinal sympathetic control. Finally, we discuss why additional biochemical agents and combinational approaches may be needed to completely ameliorate this condition.

Cell transplantation for spinal cord injury: a systematic review

Cell transplantation, as a therapeutic intervention for spinal cord injury (SCI), has been extensively studied by researchers in recent years. A number of different kinds of stem cells, neural progenitors, and glial cells have been tested in basic research, and most have been excluded from clinical studies because of a variety of reasons, including safety and efficacy. The signaling pathways, protein interactions, cellular behavior, and the differentiated fates of experimental cells have been studied in vitro in detail. Furthermore, the survival, proliferation, differentiation, and effects on promoting functional recovery of transplanted cells have also been examined in different animal SCI models. However, despite significant progress, a "bench to bedside" gap still exists. In this paper, we comprehensively cover publications in the field from the last years. The most commonly utilized cell lineages were covered in this paper and specific areas covered include survival of grafted cells, axonal regeneration and remyelination, sensory and motor functional recovery, and electrophysiological improvements. Finally we also review the literature on the in vivo tracking techniques for transplanted cells.

Cellular treatments for spinal cord injury: the time is right for clinical trials

More than 1 million people in the United States live with a spinal cord injury (SCI). Despite medical advances, many patients with SCIs still experience substantial neurological disability, with loss of motor, sensory, and autonomic function. Cell therapy is ideally suited to address the multifactorial nature of the secondary events following SCI. Remarkable advances in our understanding of the pathophysiology of SCI, structural and functional magnetic resonance imaging, image-guided micro-neurosurgical techniques, and transplantable cell biology have enabled the use of cell-based regenerative techniques in the clinic. It is important to note that there are more than a dozen recently completed, ongoing, or recruiting cell therapy clinical trials for SCI that reflect the views of many key stakeholders. The field of regenerative neuroscience has reached a stage in which the clinical trials are scientifically and ethically justified. Although experimental models and analysis methods and techniques continue to evolve, no model will completely replicate the human condition. It is recognized that more work with cervical models of contusive/compressive SCI are required in parallel with clinical trials. It is also important that the clinical translation of advances made through well-established and validated experimental approaches in animal models move forward to meet the compelling needs of individuals with SCI and to advance the field of regenerative neuroscience. However, it is imperative that such efforts at translation be done in the most rigorous and informed fashion to determine safety and possible efficacy, and to provide key information to clinicians and basic scientists, which will allow improvements in regenerative techniques and the validation and refinement of existing preclinical animal models and research approaches. The field of regenerative neuroscience should not be stalled at the animal model stage, but instead the clinical trials need to be focused, safe, and ethical, backed up by a robust, translationally relevant preclinical research strategy.

Olfactory ensheathing cells from the nose: clinical application in human spinal cord injuries

Olfactory mucosa, the sense organ of smell, is an adult tissue that is regenerated and repaired throughout life to maintain the integrity of the sense of smell. When the sensory neurons of the olfactory epithelium die they are replaced by proliferation of stem cells and their axons grow from the nose to brain assisted by olfactory ensheathing cells located in the lamina propria beneath the sensory epithelium. When transplanted into the site of traumatic spinal cord injury in rat, olfactory lamina propria or purified olfactory ensheathing cells promote behavioural recovery and assist regrowth of some nerves in the spinal cord. A Phase I clinical trial demonstrated that autologous olfactory ensheathing cell transplantation is safe, with no adverse outcomes recorded for three years following transplantation. Autologous olfactory mucosa transplantation is also being investigated in traumatic spinal cord injury although this whole tissue contains many cells in addition to olfactory ensheathing cells, including stem cells. If olfactory ensheathing cells are proven therapeutic for human spinal cord injury there are several important practical issues that will need to be solved before they reach general clinical application. This article is part of a Special Issue entitled: Understanding olfactory ensheathing glia and their prospect for nervous system repair.

Structural neuroplasticity following T5 spinal cord transection: increased cardiac sympathetic innervation density and SPN arborization

When the spinal cord is injured at or below thoracic level 5 (T5), cardiovascular control is markedly unbalanced as the heart and blood vessels innervated by upper thoracic segments remain under brain stem control, whereas the vasculature of the lower body is affected by unregulated spinal reflexes. Importantly, the regulation of heart rate and cardiac function is abnormal after spinal cord injury (SCI) at T5 because sympathetic outflow to the heart is increased. An increase in tonic sympathetic outflow may be attributable to multiple mechanisms, such as increases in cardiac sympathetic innervation density, altered morphology of stellate ganglia neurons, and/or structural neuroplasticity of cardiac sympathetic preganglionic neurons (SPNs). Furthermore, these neuroplastic changes associated with SCI may be mediated by nerve growth factor (NGF). NGF is a neurotrophin that supports the survival and differentiation of sympathetic neurons and enhances target innervation. Therefore, we tested the hypothesis that T5 spinal cord transection (T5X) is associated with an increased left ventricular (LV) NGF content, LV sympathetic innervation density, and cardiac SPN arborization. In intact and paraplegic (9 wk posttransection) rats, LV NGF content (ELISA), LV sympathetic innervation density (tyrosine hydroxylase immunohistochemistry), and cardiac SPN arborization (cholera toxin B immunohistochemistry and Sholl Analysis) were determined. Paraplegia, compared with intact, significantly increased LV NGF content, LV sympathetic innervation density, and cardiac SPN arborization. Thus, altered autonomic behavior following SCI is associated with structural neuroplastic modifications.

Selected changes in spinal cord morphology after T4 transection and olfactory ensheathing cell transplantation

Spinal cord transection at T4 results in severe damage of the nervous tissue, with impairment of motor, sensory and autonomic functions. Transplantation of olfactory ensheathing cells (OECs) has the potential to improve these functions through a number of mechanisms, which include facilitation of regeneration and neuroprotection. For cardiovascular functions, we have previously shown that OECs reduce the duration of autonomic dysreflexia, without evidence of regeneration. To further understand the mechanisms underpinning this improvement, we have studied changes in selected morphological features (cavitation, non-cavity tissue loss, morphology of sympathetic preganglionic neurons and primary afferent fibre density) in the T4-transected rat spinal cord over 9 weeks, both in control and OEC-transplanted animals. T4 transection led to a number of structural changes: gradual formation of cavities, non-cavity tissue loss, a long-term increase in soma size of sympathetic preganglionic neurons and a temporary increase in the extent of their dendritic arbours, and an increase in the density of primary afferent fibres caudal to the lesion. OECs decreased the cavitation and normalised soma size of the sympathetic preganglionic neurons below the lesion, while increasing the extent of dendritic arbours in the preganglionic neurons above the lesion. Thus the OECs may contribute to the normalisation of the dysreflexic hypertension through tissue preservation and normalisation of the morphology of the preganglionic neurons caudal to the lesion, while enhancing the input on the rostral preganglionic neurons, whose vasomotor control remains intact. We hypothesise that these changes are mediated through secretion of soluble trophic factors by the transplanted OECs.

Construction of pathways to promote axon growth within the adult central nervous system

Inducing significant axon growth or regeneration after spinal cord injury has been difficult, primarily due to the poor growth supportive environment and low intrinsic growth ability of neurons within the CNS. Neurotrophins alone have been shown to readily induce regeneration of sensory axons after dorsal root lesions, however if neurotrophin gradients are expressed within the spinal cord these axons fail to terminate within appropriate target regions. Under such conditions, addition of a "stop" signal reduces growth into deeper dorsal laminae to support more specific targeting. Such neurotrophin gradients alone lose their effectiveness when lesions are within the spinal cord, requiring a combined treatment regime. Construction of pathways using combined treatments support good regeneration when they increase the intrinsic growth properties of neurons, provide a bridge across the lesion site, and supply a growth supportive substrate to induce axon growth out of the bridge and back into the host. Neurotrophin gradients distal to the bridge greatly enhance axon outgrowth. In disorders where neuronal circuits are lost, construction of preformed growth supportive pathways sustain long distance axon growth from a neuronal transplant to distal target locations.