Central nervous system regeneration: mission impossible?

Recent advances in nanomaterials for neural applications: opportunities and challenges

Nanomedicines are promising for delivering drugs to the central nervous system, though their precision is still being improved. Fortifying nanoparticles with vital molecules can interact with the blood-brain barrier, enabling access to brain tissue. This study summarizes recent advances in nanomedicine to treat neurological complications. The integration of nanotechnology into cell biology aids in the study of brain cells' interactions. Magnetic microhydrogels have exhibited superior neuron activation compared with superparamagnetic iron oxide nanoparticles and hold promise for neuropsychiatric disorders. Nanomaterials have shown notable results, such as tackling neurodegenerative diseases by hindering harmful protein buildup and regulating cellular processes. However, further studies of the safety and effectiveness of nanoparticles in managing neurological diseases and disorders are still required.

The Role of Interstitial Fluid Pressure in Cerebral Porous Biomaterial Integration

Recent advances in biomaterials offer new possibilities for brain tissue reconstruction. Biocompatibility, provision of cell adhesion motives and mechanical properties are among the present main design criteria. We here propose a radically new and potentially major element determining biointegration of porous biomaterials: the favorable effect of interstitial fluid pressure (IFP). The force applied by the lymphatic system through the interstitial fluid pressure on biomaterial integration has mostly been neglected so far. We hypothesize it has the potential to force 3D biointegration of porous biomaterials. In this study, we develop a capillary hydrostatic device to apply controlled in vitro interstitial fluid pressure and study its effect during 3D tissue culture. We find that the IFP is a key player in porous biomaterial tissue integration, at physiological IFP levels, surpassing the known effect of cell adhesion motives. Spontaneous electrical activity indicates that the culture conditions are not harmful for the cells. Our work identifies interstitial fluid pressure at physiological negative values as a potential main driver for tissue integration into porous biomaterials. We anticipate that controlling the IFP level could narrow the gap between in vivo and in vitro and therefore decrease the need for animal screening in biomaterial design.

A Century of Brain Regeneration Phenomena and Neuromorphological Research Advances, 1890s-1990s-Examining the Practical Implications of Theory Dynamics in Modern Biomedicine

The modern thesis regarding the "structural plastic" properties of the brain, as reactions to injuries, to tissue damage, and to degenerative cell apoptosis, can hardly be seen as expendable in clinical neurology and its allied disciplines (including internal medicine, psychiatry, neurosurgery, radiology, etc.). It extends for instance to wider research areas of clinical physiology and neuropsychology which almost one hundred years ago had been described as a critically important area for the brain sciences and psychology alike. Yet the mounting evidence concerning the range of structural neuroplastic phenomena beyond the significant early 3 years of childhood has shown that there is a progressive building up and refining of neural circuits in adaptation to the surrounding environment. This review essay explores the history behind multiple biological phenomena that were studied and became theoretically connected with the thesis of brain regeneration from Santiago Ramón y Cajal's pioneering work since the 1890s to the beginning of the American "Decade of the Brain" in the 1990s. It particularly analyzes the neuroanatomical perspectives on the adaptive capacities of the Central Nervous System (CNS) as well as model-like phenomena in the Peripheral Nervous System (PNS), which were seen as displaying major central regenerative processes. Structural plastic phenomena have assumed large implications for the burgeoning field of regenerative or restorative medicine, while they also pose significant epistemological challenges for related experimental and theoretical research endeavors. Hereafter, early historical research precursors are examined, which investigated brain regeneration phenomena in non-vertebrates at the beginning of the 20th century, such as in light microscopic studies and later in electron microscopic findings that substantiated the presence of structural neuroplastic phenomena in higher cortical substrates. Furthermore, Experimental physiological research in hippocampal in vivo models of regeneration further confirmed and corroborated clinical physiological views, according to which "structural plasticity" could be interpreted as a positive regenerative CNS response to brain damage and degeneration. Yet the underlying neuroanatomical mechanisms remained to be established and the respective pathway effects were only conveyed through the discovery of neural stem cells in in adult mammalian brains in the early 1990s. Experimental results have since emphasized the genuine existence of adult neurogenesis phenomena in the CNS. The focus in this essay will be laid here on questions of the structure and function of scientific concepts, the development of research schools among biomedical investigators, as well as the impact of new data and phenomena through innovative methodologies and laboratory instruments in the neuroscientific endeavors of the 20th century.

The promising rise of bioprinting in revolutionalizing medical science: Advances and possibilities

Bioprinting is a relatively new yet evolving technique predominantly used in regenerative medicine and tissue engineering. 3D bioprinting techniques combine the advantages of creating Extracellular Matrix (ECM)like environments for cells and computer-aided tailoring of predetermined tissue shapes and structures. The essential application of bioprinting is for the regeneration or restoration of damaged and injured tissues by producing implantable tissues and organs. The capability of bioprinting is yet to be fully scrutinized in sectors like the patient-specific spatial distribution of cells, bio-robotics, etc. In this review, currently developed experimental systems and strategies for the bioprinting of different types of tissues as well as for drug delivery and cancer research are explored for potential applications. This review also digs into the most recent opportunities and future possibilities for the efficient implementation of bioprinting to restructure medical and technological practices.

3D Printed Neural Regeneration Devices

Neural regeneration devices interface with the nervous system and can provide flexibility in material choice, implantation without the need for additional surgeries, and the ability to serve as guides augmented with physical, biological (e.g., cellular), and biochemical functionalities. Given the complexity and challenges associated with neural regeneration, a 3D printing approach to the design and manufacturing of neural devices could provide next-generation opportunities for advanced neural regeneration via the production of anatomically accurate geometries, spatial distributions of cellular components, and incorporation of therapeutic biomolecules. A 3D printing-based approach offers compatibility with 3D scanning, computer modeling, choice of input material, and increasing control over hierarchical integration. Therefore, a 3D printed implantable platform could ultimately be used to prepare novel biomimetic scaffolds and model complex tissue architectures for clinical implants in order to treat neurological diseases and injuries. Further, the flexibility and specificity offered by 3D printed in vitro platforms have the potential to be a significant foundational breakthrough with broad research implications in cell signaling and drug screening for personalized healthcare. This progress report examines recent advances in 3D printing strategies for neural regeneration as well as insight into how these approaches can be improved in future studies.

Bioscaffold-Induced Brain Tissue Regeneration

Brain tissue lost after a stroke is not regenerated, although a repair response associated with neurogenesis does occur. A failure to regenerate functional brain tissue is not caused by the lack of available neural cells, but rather the absence of structural support to permit a repopulation of the lesion cavity. Inductive bioscaffolds can provide this support and promote the invasion of host cells into the tissue void. The putative mechanisms of bioscaffold degradation and its pivotal role to permit invasion of neural cells are reviewed and discussed in comparison to peripheral wound healing. Key differences between regenerating and non-regenerating tissues are contrasted in an evolutionary context, with a special focus on the neurogenic response as a conditio sine qua non for brain regeneration. The pivotal role of the immune system in biodegradation and the formation of a neovasculature are contextualized with regeneration of peripheral soft tissues. The application of rehabilitation to integrate newly forming brain tissue is suggested as necessary to develop functional tissue that can alleviate behavioral impairments. Pertinent aspects of brain tissue development are considered to provide guidance to produce a metabolically and functionally integrated de novo tissue. Although little is currently known about mechanisms involved in brain tissue regeneration, this review outlines the various components and their interplay to provide a framework for ongoing and future studies. It is envisaged that a better understanding of the mechanisms involved in brain tissue regeneration will improve the design of biomaterials and the methods used for implantation, as well as rehabilitation strategies that support the restoration of behavioral functions.

A roadmap for promoting endogenous in situ tissue restoration using inductive bioscaffolds after acute brain injury

The regeneration of brain tissue remains one of the greatest unsolved challenges in medicine and by many is considered unfeasible. Indeed, the adult mammalian brain does not regenerate tissue, but there is ongoing endogenous neurogenesis, which is upregulated after injury and contributes to tissue repair. This endogenous repair response is a conditio sine que non for tissue regeneration. However, scarring around the lesion core and cavitation provide unfavorable conditions for tissue regeneration in the brain. Based on the success of using extracellular matrix (ECM)-based bioscaffolds in peripheral soft tissue regeneration, it is plausible that the provision of an inductive ECM-based hydrogel inside the volumetric tissue loss can attract neural cells and create a de novo viable tissue. Following perturbation theory of these successes in peripheral tissues, we here propose 9 perturbation parts (i.e. requirements) that can be solved independently to create an integrated series to build a functional and integrated de novo neural tissue. Necessities for tissue formation, anatomical and functional connectivity are further discussed to provide a new substrate to support the improvement of behavioral impairments after acute brain injury. We also consider potential parallel developments of this tissue engineering effort that can support therapeutic benefits in the absence of de novo tissue formation (e.g. structural support to veterate brain tissue). It is envisaged that eventually top-down inductive "natural" bioscaffolds composed of decellularized tissues (i.e. ECM) will be replaced by bottom-up synthetic designer hydrogels that will provide very defined structural and signaling properties, potentially even opening up opportunities we currently do not envisage using natural materials.

Biodegradation of ECM hydrogel promotes endogenous brain tissue restoration in a rat model of stroke

The brain is considered to have a limited capacity to repair damaged tissue and no regenerative capacity following injury. Tissue lost after a stroke is therefore not spontaneously replaced. Extracellular matrix (ECM)-based hydrogels implanted into the stroke cavity can attract endogenous cells. These hydrogels can be formulated at different protein concentrations that govern their rheological and inductive properties. We evaluated histologically 0, 3, 4 and 8 mg/mL of porcine-derived urinary bladder matrix (UBM)-ECM hydrogel concentrations implanted in a 14-day old stroke cavity. Less concentrated hydrogels (3 and 4 mg/mL) were efficiently degraded with a 95% decrease in volume by 90 days, whereas only 32% of the more concentrated and stiffer hydrogel (8 mg/mL) was resorbed. Macrophage infiltration and density within the bioscaffold progressively increased in the less concentrated hydrogels and decreased in the 8 mg/mL hydrogels. The less concentrated hydrogels showed a robust invasion of endothelial cells with neovascularization. No neovascularization occurred with the stiffer hydrogel. Invasion of neural cells increased with time in all hydrogel concentrations. Differentiation of neural progenitors into mature neurons with axonal projections was evident, as well as a robust invasion of oligodendrocytes. However, relatively few astrocytes were present in the ECM hydrogel, although some were present in the newly forming tissue between degrading scaffold patches. Implantation of an ECM hydrogel partially induced neural tissue restoration, but a more complete understanding is required to evaluate its potential therapeutic application. STATEMENT OF SIGNIFICANCE: Extracellular matrix hydrogel promotes tissue regeneration in many peripheral soft tissues. However, the brain has generally been considered to lack the potential for tissue regeneration. We here demonstrate that tissue regeneration in the brain can be achieved using implantation of ECM hydrogel into a tissue cavity. A structure-function relationship is key to promote tissue regeneration in the brain. Specifically, weaker hydrogels that were retained in the cavity underwent an efficient biodegradation within 14 days post-implantation to promote a tissue restoration within the lesion cavity. In contrast, stiffer ECM hydrogel only underwent minor biodegradation and did not lead to a tissue restoration. Inductive hydrogels weaker than brain tissue provide the appropriate condition to promote an endogenous regenerative response that restores tissue in a cavity. This approach offers new avenues for the future treatment of chronic tissue damage caused by stroke and other acute brain injuries.

3D Printed Stem-Cell Derived Neural Progenitors Generate Spinal Cord Scaffolds

A bioengineered spinal cord is fabricated via extrusion-based multi-material 3D bioprinting, in which clusters of induced pluripotent stem cell (iPSC)-derived spinal neuronal progenitor cells (sNPCs) and oligodendrocyte progenitor cells (OPCs) are placed in precise positions within 3D printed biocompatible scaffolds during assembly. The location of a cluster of cells, of a single type or multiple types, is controlled using a point-dispensing printing method with a 200 μm center-to-center spacing within 150 μm wide channels. The bioprinted sNPCs differentiate and extend axons throughout microscale scaffold channels, and the activity of these neuronal networks is confirmed by physiological spontaneous calcium flux studies. Successful bioprinting of OPCs in combination with sNPCs demonstrates a multicellular neural tissue engineering approach, where the ability to direct the patterning and combination of transplanted neuronal and glial cells can be beneficial in rebuilding functional axonal connections across areas of central nervous system (CNS) tissue damage. This platform can be used to prepare novel biomimetic, hydrogel-based scaffolds modeling complex CNS tissue architecture in vitro and harnessed to develop new clinical approaches to treat neurological diseases, including spinal cord injury.

Inhibition of mammalian target of rapamycin complex 1 signaling by n-3 polyunsaturated fatty acids promotes locomotor recovery after spinal cord injury

The present study aimed to explore the effects of n‑3 polyunsaturated fatty acids (PUFAs) on autophagy and their potential for promoting locomotor recovery after spinal cord injury (SCI). Primary neurons were isolated and cultured. Sprague‑Dawley rats were randomly divided into three groups and fed diets with different amounts of n‑3 PUFAs. A model of spinal cord contusion was created at the T10 spinal segment and the composition of PUFAs was analyzed using gas chromatography. Spinal repair and motor function were evaluated postoperatively. Assessment of the effects of n‑3 PUFAs on autophagy and mammalian target of rapamycin complex 1 (mTORC1) was performed using immunofluorescence staining and western blotting. In vitro, n‑3 PUFAs inhibited mTORC1 and enhanced autophagy. The n‑3 PUFA levels and the ratio of n‑3 PUFA to n‑6 PUFA in the spinal cord and serum of rats fed a high‑n‑3 PUFA diet were higher before and after operation (P<0.05). Additionally, rats in the high‑n‑3 PUFA group showed improved motor function recovery, spinal cord repair‑related protein expression level (MBP, Galc and GFAP). Expression levels if these protiens in the high‑n‑3 PUFA diet group expressed the highest levels, followed by the low‑n‑3 PUFA diet group and finally the control group (P<0.05). high‑n‑3 PUFA diet promoted autophagy ability and inhibited activity of the mTORC1 signaling pathway compared with the low‑n‑3 PUFA diet group or the control group (P<0.05). These results suggest that exogenous dietary n‑3 PUFAs can inhibit mTORC1 signaling and enhance autophagy, promoting functional recovery of rats with SCI.

Axonal Sprouting and Neuronal Connectivity following Central Nervous System Insult: Implications for Occupational Therapy

Based on selected contemporary research, this paper presents a critical analysis of central nervous system (CNS) reorganisation following insult and the need for therapists better to understand the processes that constitute reorganisation and their possible contribution to the development of spasticity. In the treatment of the sequelae of CNS lesions, the synaptic reorganisation as a result of losses caused by injury - in the form of axonal sprouting - is illustrated, focusing on neuronal reconnectivity. Critical analysis of laboratory, electron microscopy and other animal and human studies is also conducted to integrate the controversies identified and to highlight the concepts that become relevant for occupational therapists, in order to optimise therapeutic intervention for maximising restitution in patients with CNS insult. The paper further discusses the capacity of the CNS to compensate and the need to utilise occupational therapy interventions, such as imagining, mental rehearsals, constraint-induced therapy, virtual reality, biofeedback and the traditional repetitive tasks, which leads to ensuring and facilitating the emergence of new synapses to perform motor tasks and manual skills and to prevent secondary changes. These external stimulations provided by the therapists are likely to stimulate both the damaged hemisphere cross-innervation and/or collateral sprouting. These scientifically based treatment strategies and neurological rehabilitation programmes would, in turn, contribute to improving the quality of life of people with CNS insult.

Gold Nanoparticle-Decorated Scaffolds Promote Neuronal Differentiation and Maturation

Engineered 3D neuronal networks are considered a promising approach for repairing the damaged spinal cord. However, the lack of a technological platform encouraging axonal elongation over branching may jeopardize the success of such treatment. To address this issue we have decorated gold nanoparticles on the surface of electrospun nanofiber scaffolds, characterized the composite material, and investigated their effect on the differentiation, maturation, and morphogenesis of primary neurons and on an immature neuronal cell line. We have shown that the nanocomposite scaffolds have encouraged a longer outgrowth of the neurites, as judged by the total length of the branching trees and the length and total distance of neurites. Moreover, neurons grown on the nanocomposite scaffolds had less neurites originating out of the soma and lower number of branches. Taken together, these results indicate that neurons cultivated on the gold nanoparticle scaffolds prefer axonal elongation over forming complex branching trees. We envision that such cellular constructs may be useful in the future as implantable cellular devices for repairing damaged neuronal tissues, such as the spinal cord.

Synergistic actions of olomoucine and bone morphogenetic protein-4 in axonal repair after acute spinal cord contusion

To determine whether olomoucine acts synergistically with bone morphogenetic protein-4 in the treatment of spinal cord injury, we established a rat model of acute spinal cord contusion by impacting the spinal cord at the T₈ vertebra. We injected a suspension of astrocytes derived from glial-restricted precursor cells exposed to bone morphogenetic protein-4 (GDAs^BMP) into the spinal cord around the site of the injury, and/or olomoucine intraperitoneally. Olomoucine effectively inhibited astrocyte proliferation and the formation of scar tissue at the injury site, but did not prevent proliferation of GDAs^BMP or inhibit their effects in reducing the spinal cord lesion cavity. Furthermore, while GDAs^BMP and olomoucine independently resulted in small improvements in locomotor function in injured rats, combined administration of both treatments had a significantly greater effect on the restoration of motor function. These data indicate that the combined use of olomoucine and GDAs^BMP creates a better environment for nerve regeneration than the use of either treatment alone, and contributes to spinal cord repair after injury.

Combined transplantation of GDAs(BMP) and hr-decorin in spinal cord contusion repair

Following spinal cord injury, astrocyte proliferation and scar formation are the main factors inhibiting the regeneration and growth of spinal cord axons. Recombinant decorin suppresses inflammatory reactions, inhibits glial scar formation, and promotes axonal growth. Rat models of T₈ spinal cord contusion were created with the NYU impactor and these models were subjected to combined transplantation of bone morphogenetic protein-4-induced glial-restricted precursor-derived astrocytes and human recombinant decorin transplantation. At 28 days after spinal cord contusion, double-immunofluorescent histochemistry revealed that combined transplantation inhibited the early inflammatory response in injured rats. Furthermore, brain-derived neurotrophic factor, which was secreted by transplanted cells, protected injured axons. The combined transplantation promoted axonal regeneration and growth of injured motor and sensory neurons by inhibiting astrocyte proliferation and glial scar formation, with astrocytes forming a linear arrangement in the contused spinal cord, thus providing axonal regeneration channels.

Acellular spinal cord scaffold seeded with bone marrow stromal cells protects tissue and promotes functional recovery in spinal cord-injured rats

Therapy using scaffolds seeded with stem cells plays an important role in repair of spinal cord injury (SCI), with the transplanted cells differentiating into nerve cells to replace the lost tissue while releasing neurotrophic factors that contribute to repair following SCI and enhance the function of the damaged nervous system. The present study investigated the ability to extend the survival time of bone marrow stromal cells (BMSCs) to restore the damaged spinal cord and improve functional recovery by grafting acellular spinal cord (ASC) scaffold seeded or not with BMSCs in a rat model of acute hemisected SCI. BBB scores revealed that treatment with BMSCs seeded into ASC scaffold led to an obvious improvement in motor function recovery compared with treatment with ASC scaffold alone or untreated controls. This improvement was evident at 2 and 8 weeks after surgery (P < 0.05). When BMSCs labeled with 5-bromodeoxyuridine were implanted together with ASC scaffold into the injured sites, they differentiated into glial cells, and some BMSCs could be observed within the graft by immunofluorescent staining at 8 weeks after implantation. Evaluation of caspase-3 activation suggested that the graft group was able to reduce apoptosis compared with SCI alone at 8 weeks after operation (P < 0.05). This study suggests that ASC scaffolds have the ability to enhance BMSC survival and improve differentiation and could also reduce native damaged nerve tissue apoptosis, thus protecting host tissue as well as improving functional recovery after implantation.

Preparation and characterization of genipin-crosslinked rat acellular spinal cord scaffolds

The feasibility of rat acellular spinal cord scaffolds for tissue engineering applications was investigated. Fresh rat spinal cords were decellularized and crosslinked with genipin (GP) to improve their structural stability and mechanical properties. The GP-crosslinked spinal cord scaffolds possessed a porous structure with an average pore diameter of 31.1 μm and a porosity of 81.5%. The resultant scaffolds exhibited a water uptake ratio of 229%, and moderate in vitro degradation rates of less than 5% in phosphate-buffered saline (PBS) and slightly more than 20% in trypsin-containing buffer, within 14 days. The ultimate tensile strength and elastic modulus of GP-crosslinked spinal cord scaffolds were determined to be 0.193±0.064 MPa and 1.541±0.082 MPa, respectively. Compared with glutaraldehyde (GA)-crosslinked acellular spinal cord scaffolds, GP-crosslinked scaffolds demonstrated similar microstructure and mechanical properties but superior biocompatibility as indicated by cytotoxicity evaluation and rat mesenchymal stem cell (MSC) adhesion behavior. Cells were able to penetrate throughout the crosslinked scaffold due to the presence of an interconnected porous structure. The low cytotoxicity of GP facilitated cell proliferation and extracellular matrix (ECM) secretion in vitro on the crosslinked scaffolds over 7 days. Thus, these GP-crosslinked spinal cord scaffolds show great promise for tissue engineering applications.

Material-driven differentiation of induced pluripotent stem cells in neuron growth factor-grafted poly(ε-caprolactone)-poly(β-hydroxybutyrate) scaffolds

The potential of constructs comprising induced pluripotent stem (iPS) cells and biopolymers can be high for neurological surgery practice, if the systematic activity of neuronal regeneration is clarified. This study shows a guided differentiation of iPS cells toward neurons in neuron growth factor (NGF)-grafted poly(ε-caprolactone) (PCL)-poly(β-hydroxybutyrate) (PHB) scaffolds. The porosity of PCL-PHB scaffolds enhanced with increasing the concentration of salt particles (porogen) and the weight percentage of PCL. An increase in the graft concentration of NGF elevated the atomic ratios of N/C and O/C on the surface of NGF-grafted PCL-PHB scaffolds. In addition, incorporating heparin and NGF promoted the adhesion and viability of iPS cells in constructs. When the weight percentage of PCL increased, the viability of iPS cells reduced; however, more PCL in constructs benefited the adhesion of iPS cells. Under the influence of heparin and NGF, a high weight percentage of PCL and a long inductive period improved iPS cells to differentiate into neuron-like cells carrying βIII tubulin and inhibited other differentiation(s). The material-driven differentiation in NGF-grafted PCL-PHB constructs can be promising in guiding iPS cells to produce neurons for nerve tissue engineering.

Live imaging of axon stretch growth in embryonic and adult neurons

Strategies for nervous system repair arise from knowledge of growth mechanisms via a growth cone. The distinctive process of axon stretch growth is a robust, long-term growth that may reveal new pathways to accelerate nerve repair. Here, a live imaging bioreactor was engineered to closely explore cellular events initiated by applied tension. The stretch growth potential between adult and embryonic dorsal root ganglion (DRG) neurons was investigated, an important difference in nerve repair. Embryonic axons were capable of unidirectional stretch growth rates of 4?mm/d and reliably reached 4?cm in length within 2 weeks. Adult axons could only reach 2?mm/d and took over 3 weeks to reach 4?cm. Utilizing time-lapse imaging, we observed growth cone motility in coordination with stretch growth. Upon initiation of stretching, growth cones retracted. However, within 10?h of continuous stretching, growth cones extended at a rate of 0.2?mm/d opposite the direction of applied tension, contributing to overall axon elongation. We analyzed fast mitochondrial transport under increasing levels of strain to determine the effect of stretch on axonal transport. Transport began to diminish at 24% strain, and was almost completely absent at 39% strain. Surprisingly, axons recovered and were capable of subsequent stretch growth. When tension was completely released (?5% strain), stretch grown axons retracted at rates up to 6.1??m/sec and slowed as resting tension was restored. This ability to assess the process of axon stretch growth in real time will allow detailed study of how tension can be used to drive axonal growth and retraction.

Preparation of the acellular scaffold of the spinal cord and the study of biocompatibility

STUDY DESIGN

Acellular spinal cord was prepared through chemical extraction, and its biocompatibility was studied.

OBJECTIVE

Acellular scaffolds have been developed from various materials for tissue reconstruction, except for spinal cord. The objective of this study was to prepare acellular spinal cord and examine the biocompatibility of the scaffold.

SETTING

This study was conducted at the Department of Orthopedics, Xinqiao Hospital, The Third Military Medical University, Chongqing, China.

METHODS

The morphology of the acellular segments was revealed by scanning electron microscopy, immunohistochemistry, and hematoxylin and eosin stain. Biocompatibility was studied by immunohistochemistry.

RESULTS

Results show that in spinal cord scaffolds, cells, myelin sheath and axon of nerve fibers were eliminated, and three-dimensional supports of extracellular matrix were reserved. The component analytical results of the acellular spinal cord indicate that they contain laminin, fibronectin and collagen, which can facilitate and induce the regeneration of injured nerves, and enhance the adhesion and proliferation of cells. The acellular spinal cord has a three-dimensional structure and excellent biocompatibility.

CONCLUSION

Our data indicate that acellular spinal cord has certain biological properties and it may be a potential alternative scaffold for spinal cord tissue engineering.

Designer protein-based scaffolds for neural tissue engineering

A key attribute missing from many current biomaterials is the ability to independently tune multiple biomaterial properties without simultaneously affecting other material parameters. Because cells are well known to respond to changes in the initial elastic modulus, degradation rate, and cell adhesivity of a biomaterial, it is critical to develop synthetic design strategies that allow decoupled tailoring of each individual parameter in order to systematically optimize cell-scaffold interactions. We present the development of a family of biomimetic scaffolds composed of chemically crosslinked, elastin-like proteins designed to support neural regeneration through a combination of cell adhesion and cell-induced degradation and remodeling. Through use of a modular protein-design strategy, a range of biomaterials is created that allows independent tuning over the initial elastic modulus, degradation rate, cell adhesivity, and neurite outgrowth. By combining these engineered proteins into composite structures, biomaterials are created with 3D patterns that emerge over time in response to cell-secreted enzymes. These dynamic 3D structures enable the delivery of multiple drugs with precise spatial and temporal resolution and also enable the design of biomaterials that adapt to changing scaffold needs.

Effects of corticospinal tract stimulation on renal sympathetic nerve activity in rats with intact and chronically lesioned spinal cords

Sympathetic preganglionic neurons and interneurons are closely apposed (presumably synapsed upon) by corticospinal tract (CST) axons. Sprouting of the thoracic CST rostral to lumbar spinal cord injuries (SCI) substantially increases the incidence of these appositions. To test our hypothesis that these additional synapses would increase CST control of sympathetic activity after SCI, we measured the effects of electrical stimulation of the CST on renal sympathetic nerve activity (RSNA) and arterial pressure (AP) in alpha-chloralose-anesthetized rats with either chronically intact or chronically lesioned spinal cords. Stimuli were delivered to the CST at intensities between 25-150 muA and frequencies between 25 and 75 Hz. Stimulation of the CST at the midcervical level decreased RSNA and AP. These decreases were not mediated by direct projections of the CST to the thoracic spinal cord because we could still elicit them by midcervical stimulation after acute lesions of the CST at caudal cervical levels. In contrast, caudal thoracic CST stimulation increased RSNA and AP. Neither the responses to cervical nor thoracic stimulation were affected by chronic lumbar SCI. These data show that the CST mediates decreases in RSNA via a cervical spinal system but excites spinal sympathetic neurons at caudal thoracic levels. Because chronic lumber spinal cord injury affected responses evoked from neither the cervical nor thoracic CST, we conclude that lesion-induced or regeneration-induced formation of new synapses between the CST and sympathetic neurons may not affect cardiovascular regulation.

Adult rat spinal cord culture on an organosilane surface in a novel serum-free medium

In this study, we have documented by morphological analysis, immunocytochemistry, and electrophysiology, the development of a culture system that promotes the growth and long-term survival of dissociated adult rat spinal cord neurons. This system comprises a patternable, nonbiological, cell growth-promoting organosilane substrate coated on a glass surface and an empirically derived novel serum-free medium, supplemented with specific growth factors (acidic fibroblast growth factor, heparin sulfate, neurotrophin-3, brain-derived neurotrophic factor, glial-derived neurotrophic factor, cardiotrophin-1, and vitronectin). Neurons were characterized by immunoreactivity for neurofilament 150, neuron-specific enolase, Islet-1 antibodies, electrophysiology, and the cultures were maintained for 4-6 wk. This culture system could be a useful tool for the study of adult mammalian spinal neurons in a functional in vitro system.

Development of transplantable nervous tissue constructs comprised of stretch-grown axons

Pursuing a new approach to nervous system repair, fasciculated axon tracts grown in vitro were developed into nervous tissue constructs designed to span peripheral nerve or spinal cord lesions. We optimized the newfound process of extreme axon stretch growth to maximize the number and length of axon tracts, reach an unprecedented axon growth-rate of 1cm/day, and create 5cm long axon tracts in 8 days to serve as the core component of a living nervous tissue construct. Immunocytochemical analysis confirmed that elongating fibers were axons, and that all major cytoskeletal constituents were present across the stretch-growth regions. We formed a transplantable nervous tissue construct by encasing the elongated cells in an 80% collagen hydrogel, removing them from culture, and inserting them into a synthetic conduit. Alternatively, we induced axon stretch growth directly on a surgical membrane that could be removed from the elongation device, and formed into a cylindrical construct suitable for transplant. The ability to rapidly create living nervous tissue constructs that recapitulates the uniaxial orientations of the original nerve offers an unexplored and potentially complimentary direction in nerve repair. Ideally, bridging nerve damage with living axon tracts may serve to establish or promote new functional connections.

Guided cell adhesion and outgrowth in peptide-modified channels for neural tissue engineering

A hydrogel scaffold of well-defined geometry was created and modified with laminin-derived peptides in an aqueous solution, thereby maintaining the geometry of the scaffold while introducing bioactive peptides that enhance cell adhesion and neurite outgrowth. By combining a fiber templating technique to create longitudinal channels with peptide modification, we were able to synthesize a scaffold that guided cell adhesion and neurite outgrowth of primary neurons. Scaffolds were designed to have numerous longitudinally oriented channels with an average channel diameter of 196 +/- 6 microm to ultimately promote fasciculation of regenerating cables and a compressive modulus of 192 +/- 8 kPa to match the modulus of the soft nerve tissue. Copolymerization of 2-hydroxylethyl methacrylate (HEMA) with 2-aminoethyl methacrylate (AEMA) scaffolds, provided primary amine groups to which two sulfhydryl terminated, laminin-derived oligopeptides, CDPGYIGSR and CQAASIKVAV, were covalently bound using the sulfo-(N-maleimidomethyl)cyclohexane-1-carboxylate (sulfo-SMCC) crosslinking agent. The concentration of peptides on the scaffolds was measured at 106 +/- 4 micromol/cm(2) using the ninhydrin method and 92 +/- 9 micromol/cm(2) using the BCA protein assay. The peptide modified P(HEMA-co-AEMA) scaffolds were easily fabricated in aqueous conditions, highly reproducible, well-defined, and enhanced neural cell adhesion and guided neurite outgrowth of primary chick dorsal root ganglia neurons relative to non-peptide-modified controls. The copolymerization of AEMA with HEMA can be extended to other radically polymerized monomers and is advantageous as it facilitates scaffold modification in aqueous solutions thereby obviating the use of organic solvents which can be cytotoxic and often disrupt scaffold geometry. The combination of well-defined chemical and physical stimuli described herein provides a means for guided regeneration both in vitro and in vivo.

Dural closure, cord approximation, and clot removal: enhancement of tissue sparing in a novel laceration spinal cord injury model

OBJECT

Laceration-induced spinal cord injury (SCI) results in the invasion of a connective tissue scar, progressive damage to the spinal cord due to complex secondary injury mechanisms, and axonal dieback of descending motor pathways. The authors propose that preparation of the spinal cord for repair strategies should include hematoma removal and dural closure, resulting in apposition of the severed ends of the spinal cord. Such procedures may reduce the size of the postinjury spinal cord cyst as well as limit scar formation.

METHODS

Using a novel device, the Vibraknife, the authors created a dorsal hemisection of the spinal cord at C-6 in the adult rat. In Group 1 (eight rats), the dura mater was repaired with apposition of the two stumps of the spinal cord to reduce the lesion gap. In Group 2 (10 rats), the dura was not closed and the two cord stumps were not approximated. All rats were killed at 4 weeks postinjury, and the spinal cords from each group were removed and examined using histological, stereological, and immunohistochemical methods. In Group 1 rats a significant reduction of the total lesion volume and connective tissue scar was observed compared with those in Group 2 (Student t-test, p < 0.05). Approximation of the stumps did not promote the regeneration of corticospinal tract fibers or sensory axons through the lesion site.

CONCLUSIONS

Apposition of the severed ends of the spinal cord by dural closure reduces the lesion gap, cystic cavitation, and connective tissue scar formation. These outcomes may collectively reduce secondary tissue damage at the injury site and shorten the length of the lesion gap, which will facilitate transplantation-mediated axonal regeneration after laceration-induced SCI.

HmCRIP, a cysteine-rich intestinal protein, is expressed by an identified regenerating nerve cell

A Hirudo medicinalis cDNA isolated from regenerating CNS tissue at 24 h post-axotomy was identified as a leech homologue of the mammalian cysteine-rich intestinal proteins (CRIPs) and named HmCRIP. HmCRIP is up-regulated within 6 h of axotomy, peaking at 24 h. This is the first demonstration of a CRIP homologue in regenerating CNS and in a serotonergic neurone. In rodents CRIP is an important factor in the regulation of the inflammatory immune response through control of Th1/Th2 differentiation. The role of HmCRIP in the regeneration competent environment of the annelid central nervous system is discussed.

Neurotrophin modulation of voltage-gated potassium channels in rat through TrkB receptors is time and sensory experience dependent

The whole-cell configuration of the patch-clamp technique, immunoprecipitation experiments and unilateral naris occlusions were used to investigate whether the voltage-gated potassium channel Kv1.3 was a substrate for neurotrophin-induced tyrosine phosphorylation and subsequent functional modulation of current properties in cultured rat olfactory bulb (OB) neurons. Membrane proteins of the OB included all three Trk receptor kinases, but the truncated form of the receptor, lacking an intact kinase domain, was the predominant form of the protein for TrkA and TrkC, while TrkB was predominantly found as the full-length receptor. Acute (15 min) stimulation of OB neurons with bath application of 50 ng ml(-1) brain-derived neurotrophic factor (BDNF), which is a selective ligand for TrkB, caused suppression of the whole-cell outward current and no changes in the kinetics of inactivation or deactivation. Acute stimulation with either nerve growth factor or neurotrophin-3 failed to evoke any changes in Kv1.3 function in the OB neurons. Chronic exposure to BDNF (days) caused an increase in the magnitude of Kv1.3 current and speeding of the inactivation and deactivation of the channel. Acute BDNF-induced activation of TrkB receptors significantly increased tyrosine phosphorylation of Kv1.3 in the OB, as shown using a combined immunoprecipitation and Western blot analysis. With unilateral naris occlusion, the acute BDNF-induced tyrosine phosphorylation of Kv1.3 was increased in neurons lacking odour sensory experience. In summary, the duration of neurotrophin exposure and the sensory-dependent state of a neuron can influence the degree of phosphorylation of a voltage-gated ion channel and its concomitant functional modulation by neurotrophins.

Experimental models of partial lesion of rat spinal cord to investigate neurodegeneration, glial activation, and behavior impairments

The article demonstrates two experimental models of spinal cord partial injury in rats: a contuse model promoted by the NYU impactor system and a partial hemitransection model achieved by a stereotaxic-positioned adjustable wire knife. By means of a defined impact weight (10 g) and a digital optical potentiometer linked to a computer, the impactor transferred and registered a moderate or a severe contusion to the rat spinal cord at a low thoracic level after dropping the weight from distances of 25 mm and 50 mm, respectively, to the dorsal surface of the exposed dura spinal cord. Impact curve was calculated and the parameters of the trauma, like impact velocity, cord compression distance and cord compression rates were obtained in order to demonstrate trauma severity. To promote partial hemitransection, rats were positioned in a spinal cord unit of a stereotaxic apparatus and lesion was made with the adjustable wire knife spatially oriented. By means of a computerized infrared motion sensor-home cage activity monitor and a noncomputerized evaluation of motor behavior using the inclined plane and the motor score of Tarlov tests, behavior was analyzed in an acute period postlesion. Rats were sacrificed and spinal cords were processed for routine staining to show neurons and for GFAP and OX42 immunohistochemistry to demonstrate glial cells. The tissue labelings were quantified using computer assisted stereology by means of an optical disector and microdensitometric image analysis by means of quantification of gray values of discriminated profiles. While partial hemitransection model favored a more accurate control of the lesion location, the contuse model allowed us to perform different degrees of lesion severity. A close correlation between behavioral impairment and severity of trauma was seen in the rats submitted to spinal cord contusion. The stereologic lesion index showed a correlation between severity of trauma and tissue damage by 7 days and demonstrated a time-dependent secondary degeneration after moderate but not after severe spinal cord contusion from 7 to 30 days after injury. Long-lasting activations of astrocytes and microglia seen by persisted increases in the specific mean gray values of immunoreactivities were also found in all levels of the white and gray matters of the partial hemitransected spinal cord until 3 months postinjury which can be related to wound/repair events and paracrine trophic support to spinal cord remaining neurons. The results showed that controlled partial lesions may provide an important toll to study trophism and plasticity in the spinal cord.