Adaptation of tape removal test for measurement of sensitivity in perineal area of rat

Regeneration after spinal cord injury is a goal of many studies. Although the most obvious target is to recover motor function, restoration of sensation can also improve the quality of life after spinal cord injury. For many patients, recovery of sensation in the perineal and genital area is a high priority. Currently there is no experimental test in rodents for measuring changes in sensation in the perineal and genital area after spinal cord injury. The aim of our study was to develop a behavioural test for measuring the sensitivity of the perineal and genital area in rats. We have modified the tape removal test used routinely to test sensorimotor deficits after stroke and spinal cord injury to test the perineal area with several variations. A small piece of tape (approximately 1 cm²) was attached to the perineal area. Time to first contact and to the removal of the tape was measured. Each rat was trained for 5 consecutive days and then tested weekly. We compared different rat strains (Wistar, Sprague-Dawley, Long-Evans and Lewis), both genders, shaving and non-shaving and different types of tape. We found that the test was suitable for all tested strains, however, Lewis rats achieved the lowest contact times, but this difference was significant only for the first few days of learning the task. There were no significant differences between gender and different types of tape or shaving. After training the animals underwent dorsal column lesion at T10 and were tested at day 3, 8, 14 and 21. The test detected a sensory deficit, the average time across all animals to sense the stimulus increased from 1'32 up to 3'20. There was a strong relationship between lesion size and tape detection time, and only lesions that extended laterally to the dorsal root entry zone produced significant sensory deficits. Other standard behavioural tests (BBB, von Frey, ladder and Plantar test) were performed in the same animals. There was a correlation between lesion size and deficit for the ladder and BBB tests, but not for the von Frey and Plantar tests. We conclude that the tape removal test is suitable for testing perineal sensation in rats, can be used in different strains and is appropriate for monitoring changes in sensation after spinal cord injury.

A Comparative Study of Preparation Techniques for Improving the Viability of Striatal Grafts Using Vital Stains, in Vitro Cultures, and in Vivo Grafts

Cell suspension grafts from embryonic striatal primordia placed into the adult rat striatum survive well and are able to alleviate a number of behavioral deficits caused by excitotoxic lesions to this structure. However, neither the anatomical connectivity between the graft and host nor the functional recovery elicited by the grafts is completely restored. One way in which the survival and function of embryonic striatal grafts may be enhanced is by the improvement of techniques for the preparation of the cell suspension prior to implantation, an issue that has been addressed only to a limited extent. We have evaluated a number of parameters during the preparation procedure, looking at the effects on cell survival over the first 24 h from preparation using vital dyes and the numbers of surviving neurons in vitro, after 4 days in culture, in addition to graft survival and function in vivo. Factors influencing cell survival include the type of trypsinization procedure and the age of donor tissues used for suspension preparation. The presence of DNase has no effect on cell viability but aids the dissociation of the tissue to form single cells. These results have important implications for the use of embryonic striatal grafts in animal models of Huntington's disease, and in any future clinical application of this research.

An integrin approach to axon regeneration

Axon regeneration in the CNS is blocked by inhibitory molecules in the environment and by a developmental loss of regenerative potential in CNS axons. Axon growth is a specialized form of cell migration, and for any cell to migrate there must be an adhesion molecule at the growth tip that recognizes a ligand in the environment, and which is linked to signaling and cytoskeletal mechanisms. The reasons for this loss of regenerative ability in CNS axons are several, but important contributors are the developmental loss of integrins that recognize ligands in the mature CNS environment, and selective trafficking of integrins and other molecules to exclude them from axons and direct them to dendrites. Regeneration of sensory axons in the spinal cord can be achieved by expression of tenascin-binding α9-integrin together with the integrin activator kindlin-1. This works because integrins are transported into sensory axons. Transport of integrins into retinal ganglion cell axons is seen in the retina, but may become more restricted in the optic nerve, with a subset of axons containing expressed integrins. Transduction of ganglion cells with α9-integrin and kindlin-1 should promote regeneration of this subset of axons, but attention to transport may be required for regeneration of the remaining axons.

Targeting the neural extracellular matrix in neurological disorders

The extracellular matrix (ECM) is known to regulate important processes in neuronal cell development, activity and growth. It is associated with the structural stabilization of neuronal processes and synaptic contacts during the maturation of the central nervous system. The remodeling of the ECM during both development and after central nervous system injury has been shown to affect neuronal guidance, synaptic plasticity and their regenerative responses. Particular interest has focused on the inhibitory role of chondroitin sulfate proteoglycans (CSPGs) and their formation into dense lattice-like structures, termed perineuronal nets (PNNs), which enwrap sub-populations of neurons and restrict plasticity. Recent studies in mammalian systems have implicated CSPGs and PNNs in regulating and restricting structural plasticity. The enzymatic degradation of CSPGs or destabilization of PNNs has been shown to enhance neuronal activity and plasticity after central nervous system injury. This review focuses on the role of the ECM, CSPGs and PNNs; and how developmental and pharmacological manipulation of these structures have enhanced neuronal plasticity and aided functional recovery in regeneration, stroke, and amblyopia. In addition to CSPGs, this review also points to the functions and potential therapeutic value of these and several other key ECM molecules in epileptogenesis and dementia.

Characterization of neurological recovery following traumatic sensorimotor complete thoracic spinal cord injury

STUDY DESIGN

Retrospective, longitudinal analysis of sensory, motor and functional outcomes from individuals with thoracic (T2-T12) sensorimotor complete spinal cord injury (SCI).

OBJECTIVES

To characterize neurological changes over the first year after traumatic thoracic sensorimotor complete SCI.

METHODS

A dataset of 399 thoracic complete SCI subjects from the European Multi-center study about SCI (EMSCI) was examined for neurological level, sensory levels and sensory scores (pin-prick and light touch), lower extremity motor score (LEMS), ASIA Impairment Scale (AIS) grade, and Spinal Cord Independence Measure (SCIM) over the first year after SCI.

RESULTS

AIS grade conversions were limited. Sensory scores exhibited minimal mean change, but high variability in both rostral and caudal directions. Pin-prick and light touch sensory levels, as well as neurological level, exhibited minor changes (improvement or deterioration), but most subjects remained within one segment of their initial injury level after 1 year. Recovery of LEMS occurred predominantly in subjects with low thoracic SCI. The sensory zone of partial preservation (ZPP) had no prognostic value for subsequent recovery of sensory levels or LEMS. However, after mid or low thoracic SCI, ≥3 segments of sensory ZPP correlated with an increased likelihood for AIS grade conversion.

CONCLUSION

The data suggest that a sustained deterioration of three or more thoracic sensory levels or loss of upper extremity motor function are rare events and may be useful for tracking the safety of a therapeutic intervention in early phase acute SCI clinical trials, if a significant proportion of study subjects exhibit such an ascent.

Improving RPE adhesion to Bruch's membrane

Age-related macular degeneration is the leading cause of blindness in the developing world. Retinal pigmented epithelium (RPE) transplantation in subretinal space, has been assessed in various animal models of age-related macular degeneration and in humans as a potential technique to preserve the visual function. However, the RPE cell survival posttransplantation is limited because of lack of attachment of the transplanted cells to the pathological Bruch's membrane and also partly because of iatrogenic removal of adhesive elements in the membrane during the removal of choroidal new vessels before transplantation procedure. Although pathological Bruch's membrane is well studied, there is still much debate as to why and how changes in the structure and components of this membrane leads to loss of RPE cells and disruption of their function and subsequent death of photoreceptors leading to visual loss. Integrins on RPE cells have been characterized and shown to be important for attachment of cells to Bruch's membrane. Considering the essential role of integrins in functions such as cell migration and adhesion, it is plausible that lack of attachment of RPE cells posttransplantation can be overcome by improving integrin function. Here, we have focused on some of the recent findings on the use of integrins and modulation of their function to improve the adhesion of RPE cells to normal and pathological Bruch's membrane. This work also aims at elucidating a potential mechanism by which accumulating inhibitory molecules in the Bruch's membrane in the pathological state, interferes with integrin function.

Guidelines for the conduct of clinical trials for spinal cord injury as developed by the ICCP panel: spontaneous recovery after spinal cord injury and statistical power needed for therapeutic clinical trials

The International Campaign for Cures of Spinal Cord Injury Paralysis (ICCP) supported an international panel tasked with reviewing the methodology for clinical trials in spinal cord injury (SCI), and making recommendations on the conduct of future trials. This is the first of four papers. Here, we examine the spontaneous rate of recovery after SCI and resulting consequences for achieving statistically significant results in clinical trials. We have reanalysed data from the Sygen trial to provide some of this information. Almost all people living with SCI show some recovery of motor function below the initial spinal injury level. While the spontaneous recovery of motor function in patients with motor-complete SCI is fairly limited and predictable, recovery in incomplete SCI patients (American spinal injury Association impairment scale (AIS) C and AIS D) is both more substantial and highly variable. With motor complete lesions (AIS A/AIS B) the majority of functional return is within the zone of partial preservation, and may be sufficient to reclassify the injury level to a lower spinal level. The vast majority of recovery occurs in the first 3 months, but a small amount can persist for up to 18 months or longer. Some sensory recovery occurs after SCI, on roughly the same time course as motor recovery. Based on previous data of the magnitude of spontaneous recovery after SCI, as measured by changes in ASIA motor scores, power calculations suggest that the number of subjects required to achieve a significant result from a trial declines considerably as the start of the study is delayed after SCI. Trials of treatments that are most efficacious when given soon after injury will therefore, require larger patient numbers than trials of treatments that are effective at later time points. As AIS B patients show greater spontaneous recovery than AIS A patients, the number of AIS A patients requiring to be enrolled into a trial is lower. This factor will have to be balanced against the possibility that some treatments will be more effective in incomplete patients. Trials involving motor incomplete SCI patients, or trials where an accurate assessment of AIS grade cannot be made before the start of the trial, will require large subject numbers and/or better objective assessment methods.

Guidelines for the conduct of clinical trials for spinal cord injury as developed by the ICCP Panel: clinical trial inclusion/exclusion criteria and ethics

The International Campaign for Cures of Spinal Cord Injury Paralysis established a panel tasked with reviewing the methodology for clinical trials for spinal cord injury (SCI), and making recommendations on the conduct of future trials. This is the third of four papers. It examines inclusion and exclusion criteria that can influence the design and analysis of clinical trials in SCI, together with confounding variables and ethical considerations. Inclusion and exclusion criteria for clinical trials should consider several factors. Among these are (1) the enrollment of subjects at appropriate stages after SCI, where there is supporting data from animal models or previous human studies; (2) the severity, level, type, or size of the cord injury, which can influence spontaneous recovery rate and likelihood that an experimental treatment will clinically benefit the subject; and (3) the confounding effects of various independent variables such as pre-existing or concomitant medical conditions, other medications, surgical interventions, and rehabilitation regimens. An issue of substantial importance in the design of clinical trials for SCI is the inclusion of blinded assessments and sham surgery controls: every effort should be made to address these major issues prospectively and carefully, if clear and objective information is to be gained from a clinical trial. The highest ethical standards must be respected in the performance of clinical trials, including the adequacy and clarity of informed consent.

Guidelines for the conduct of clinical trials for spinal cord injury (SCI) as developed by the ICCP panel: clinical trial outcome measures

An international panel reviewed the methodology for clinical trials of spinal cord injury (SCI), and provided recommendations for the valid conduct of future trials. This is the second of four papers. It examines clinical trial end points that have been used previously, reviews alternative outcome tools and identifies unmet needs for demonstrating the efficacy of an experimental intervention after SCI. The panel focused on outcome measures that are relevant to clinical trials of experimental cell-based and pharmaceutical drug treatments. Outcome measures are of three main classes: (1) those that provide an anatomical or neurological assessment for the connectivity of the spinal cord, (2) those that categorize a subject's functional ability to engage in activities of daily living, and (3) those that measure an individual's quality of life (QoL). The American Spinal Injury Association impairment scale forms the standard basis for measuring neurologic outcomes. Various electrophysiological measures and imaging tools are in development, which may provide more precise information on functional changes following treatment and/or the therapeutic action of experimental agents. When compared to appropriate controls, an improved functional outcome, in response to an experimental treatment, is the necessary goal of a clinical trial program. Several new functional outcome tools are being developed for measuring an individual's ability to engage in activities of daily living. Such clinical end points will need to be incorporated into Phase 2 and Phase 3 trials. QoL measures often do not correlate tightly with the above outcome tools, but may need to form part of Phase 3 trial measures.

Guidelines for the conduct of clinical trials for spinal cord injury as developed by the ICCP panel: clinical trial design

The International Campaign for Cures of Spinal Cord Injury Paralysis established a panel tasked with reviewing the methodology for clinical trials for spinal cord injury (SCI), and making recommendations on the conduct of future trials. This is the fourth of four papers. Here, we examine the phases of a clinical trial program, the elements, types, and protocols for valid clinical trial design. The most rigorous and valid SCI clinical trial would be a prospective double-blind randomized control trial utilizing appropriate placebo control subjects. However, in specific situations, it is recognized that other trial procedures may have to be considered. We review the strengths and limitations of the various types of clinical trials with specific reference to SCI. It is imperative that the design and conduct of SCI clinical trials should meet appropriate standards of scientific inquiry to insure that meaningful conclusions about efficacy and safety can be achieved and that the interests of trial subjects are protected. We propose these clinical trials guidelines for use by the SCI clinical research community.

Astrocytes promote neurogenesis from oligodendrocyte precursor cells

The oligodendrocyte precursor cell (OPC) has until recently been regarded as a lineage-restricted precursor cell. Considerable interest has been generated by reports suggesting that OPCs may possess a wider differentiation potential than previously assumed and thus be considered a multipotential stem cell. This study examined the neuronal differentiation potential of rat, postnatal cortical OPCs in response to extracellular cues in vitro and in vivo. OPCs did not exhibit intrinsic neuronal potential and were restricted to oligodendrocyte lineage potential following treatment with the neural precursor mitogen fibroblast growth factor 2. In contrast, a postnatal hippocampal astrocyte-derived signal(s) is sufficient to induce functional neuronal differentiation of cortical OPCs in vitro in population and single cell studies. Co-treatment with Noggin, a bone morphogenetic protein antagonist, did not attenuate neuronal differentiation. Following transplantation to the adult rat hippocampus, cortical OPCs expressed doublecortin, a neuroblast-associated marker. The present findings show that hippocampal, astrocyte-derived signals can induce the neuronal differentiation of OPCs through a Noggin-independent mechanism.

The injury response of oligodendrocyte precursor cells is induced by platelets, macrophages and inflammation-associated cytokines

Oligodendrocyte precursor cells recognized with the NG2 antibody respond rapidly to CNS injuries with hypertrophy and upregulation of the NG2 chondroitin sulfate proteoglycan within 24 h. These cells participate in glial scar formation, remaining around the injury site for several weeks. After injury, reactive oligodendrocyte precursor cells increase their production of several chondroitin sulfate proteoglycans, including NG2: this cell type thus represents a component of the inhibitory environment that prevents regeneration of axons in the injured CNS. This study analyzes factors that activate oligodendrocyte precursor cells. Both microglia and astrocytes become reactive around motor neurons following peripheral nerve lesions. We show that oligodendrocyte precursor cells do not hypertrophy or increase NG2 levels after these lesions. Those lesions that cause an oligodendrocyte precursor cell reaction generally open the blood-brain barrier. We therefore opened the blood-brain barrier with microinjections of vascular endothelial growth factor or lipopolysaccharide to the rat and mouse brain, and examined oligodendrocyte precursor cell reactivity after 24 h. Both treatments led to increases in NG2 and hypertrophy of oligodendrocyte precursor cells. Of directly injected blood components serum and thrombin were without effect, while platelets and macrophages activated oligodendrocyte precursor cells. We tested the effects of a range of injury-related cytokines, of which tumor necrosis factor alpha; interleukin-1; transforming growth factor beta; interferon gamma had effects on oligodendrocyte precursor cells. Oligodendrocyte precursor cell chemokines, and mitogens did not increase NG2 levels.

The effects of corticosterone and dehydroepiandrosterone on neurotrophic factor mRNA expression in primary hippocampal and astrocyte cultures

The effects of corticosterone (CORT) and dehydroepiandrosterone (DHEA) on the expression of growth factor mRNA in either primary hippocampal cultures or astrocyte-enriched cultures from E18 CD rats was studied. In mixed primary cultures, 1 microM CORT up-regulated basic fibroblast growth factor (bFGF; FGF2) after 6 h of exposure, but down-regulated nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) were unchanged. A 100 microM NMDA alone decreased NT-3, increased BDNF, but had no effect on NGF or FGF2. Concurrently administered CORT had no additional effect on either NGF, BDNF or NT-3, but up-regulated FGF2. In astrocytic cultures, 1 microM CORT increased FGF2 and NT-3, but decreased BDNF and NGF. A dose-response study confirmed these results. DHEA (100 nM) up-regulated NGF after 3 h, but not at other time points (6, 12, 24, 48 h). It had no effect on the other growth factors in mixed primary cultures. In astrocytic cultures, there was no effect of DHEA. Adding DHEA or its sulphate (up to 1 microM) to CORT did not alter the latter's action on growth factor mRNA expression. These results show that CORT has a selective action on growth factor expression, which was greater in astrocytic than in mixed cultures, that CORT amplifies or moderates activity-induced expression following NMDA, but that DHEA does not influence the effects of CORT on growth factor mRNA expression under these conditions.

The responses of oligodendrocyte precursor cells, astrocytes and microglia to a cortical stab injury, in the brain

The cortical stab injury has been widely used for biochemical analysis of molecular changes following CNS injury. However, the cellular responses to this injury have not been accurately quantified. In order to provide a baseline for biochemical studies and future experiments on the manipulation of the CNS injury response we have undertaken a quantitative analysis of this injury. The proliferative and reactive responses of oligodendrocyte precursor cells, astrocytes and microglia were measured, using antibodies to NG2, glial fibrillary acidic protein (GFAP) and the cd11-b clone OX-42 to characterise these cell types at 2, 4, 7 and 14 days post-injury. Oligodendrocyte precursors and microglia proliferated rapidly during the first week, mostly within 0.3 mm of the lesion. Of the dividing cells over 60% were oligodendrocyte precursor cells with microglia making up the balance of the dividing cells. Minimal numbers of astrocytes divided in response to the lesion. Large cells with one or two short processes that were both NG2 and OX-42 positive were identified very close to the lesion at 2 and 4 days post-lesion but not thereafter. They are likely to be blood-derived cells that express NG2 or have ingested it. NG2 immunohistochemistry and platelet-derived growth factor alpha receptor (PDGFalpha-R) in situ hybridisation on neighbouring sections was performed. In the lesioned area only 12% of NG2 positive (+ive) cells were PDGFalpha-R +ive (a ratio of 1:8 for PDGFalpha-R +ive cells: NG2 +ive cells) compared with 33% in the unlesioned cortex and an almost 100% overlap in the spinal cord.

Altered CNS response to injury in the MRL/MpJ mouse

The MRL/MpJ mouse has a greatly enhanced healing response and an absence of scarring compared with other mouse strains. Following lesions to the CNS mammals show a scarring response known as reactive gliosis, and this CNS scar tissue blocks regeneration of cut axons. We have therefore compared reactive gliosis in the MRL/MpJ mouse and the Swiss Webster mouse, which exhibits normal scarring in the periphery. The lesion model was a stab lesion to the cortex, in which reactive gliosis has previously been quantified. Axon regeneration was examined following a cut lesion to the dopaminergic projection from the substantia nigra to the striatum used in previous regeneration experiments. In the MRL/MpJ following the lesion compared with Swiss Webster mice there was greater cell loss around the lesion followed by greater and more widespread and more prolonged cellular proliferation. Early after the lesion there was a greater loss of glial fibrillary acidic protein (GFAP)-positive astrocytes around the injury site in the MRL/MpJ, and an enhancement and prolongation of the microglial inflammatory response. This was accompanied by greater and more widespread blood-brain barrier leakage following injury. RNA levels for the matrix metalloproteinases (MMP)-2 and MMP-9 as well as for the thrombin receptors PAR-1 and PAR-4 were also greater at the MRL/MpJ injury site. All of these differences were transient and by 14 days post-injury there were no differences observed between MRL/MpJ and control mice. No axonal regeneration was observed following axotomy to the nigrostriatal pathway of the MRL/MpJ or the Swiss Webster mice at any time point.

Chondroitin sulphate proteoglycans: preventing plasticity or protecting the CNS?

It is well established that axonal regeneration in the adult CNS is largely unsuccessful. Numerous axon-inhibitory molecules are now known to be present in the injured CNS, and various strategies for overcoming these obstacles and enhancing CNS regeneration have been experimentally developed. Recently, the use of chondroitinase-ABC to treat models of CNS injury in vivo has proven to be highly beneficial towards regenerating axons, by degrading the axon-inhibitory chondroitin sulphate glycosaminoglycan chains found on many proteoglycans in the astroglial scar. This enzyme has now been shown to restore synaptic plasticity in the visual cortex of adult rats by disrupting perineuronal nets, which contain high levels of chondroitin sulphate proteoglycans (CS-PGs) and are expressed postnatally around groups of certain neurons in the normal CNS. The findings suggest exciting prospects for enhancing growth and plasticity in the adult CNS; however, some protective roles of CS-PGs in the CNS have also been demonstrated. Clearly many questions concerning the mechanisms regulating expression of extracellular matrix molecules in CNS pathology remain to be answered.

Inhibiting cell proliferation during formation of the glial scar: effects on axon regeneration in the CNS

Following a CNS lesion many glial cell types proliferate and/or migrate to the lesion site, forming the glial scar. The majority of these cells express chondroitin sulphate proteoglycans (CS-PGs), previously shown to inhibit axonal growth. In this study, in an attempt to diminish glial scar formation and improve axonal regeneration, proliferating cells were eliminated from the lesion site. Adult rats received a continuous infusion of 2% cytosine-D-arabinofuranoside (araC) or saline for 7 days over the lesion site, immediately following a unilateral transection of the right medial forebrain bundle. Additional groups of rats that received subdural infusions prior to the lesion, and lesioned rats which received no infusion, were also compared in the analyses. Animals were killed at 4, 7, 12 or 18 days post-lesion (dpl) and immunohistochemistry was used to determine the effects of these treatments on tyrosine hydroxylase (TH)-lesioned axons, and on the injury response of glial cells. Almost complete elimination of NG2 oligodendrocyte progenitor cells from the lesion site was seen up to 7 dpl in araC-infused animals; reduced numbers of reactive CD11b microglia were also seen but no effects were seen on the injury response of GFAP astrocytes. Significantly more TH axons were seen distal to the lesion in araC-treated brains, but these numbers dwindled by 18 dpl.

Chondroitin sulphate proteoglycans in the central nervous system: changes and synthesis after injury

Chondroitin sulphate proteoglycans (CSPGs) are up-regulated in the central nervous system after injury, specifically around the lesion site where the glial scar forms. This structure contains astrocytes, oligodendrocyte precursor cells, microglia and meningeal cells, and forms an inhibitory substrate for axon re-growth. CSPGs have been shown to be closely involved in this neuronal growth inhibition, specifically through their sugar chains. These chains are composed of repeats of the same disaccharide unit carrying sulphate groups in different positions. The sulphation pattern directly influences the CSPG binding properties and function; the specific sulphation pattern required for the inhibitory activity of these molecules on axon growth is unknown at present. The expression of the chondroitin sulphotransferases, which sulphate the disaccharide residues of CSPGs and thus are responsible for the structural diversity of the chondroitin sulphate sugar chains, is regulated differently in central nervous system during development and after injury, suggesting the implication of a specific sulphation pattern in the inhibitory activity of CSPGs.

Regeneration in the mammalian optic nerve

Since the first studies on axonal regeneration, the optic nerve (ON) of higher vertebrates has been considered a good experimental system to investigate the failure of mature CNS neurons to re-grow after axotomy. The optic nerve is composed of a single population of fibers the RGC axons and, being separated from the rest of the brain, it is easily accessible to surgical manipulations. All the fibers can be transected without massive damage to the surrounding tissue, so their reaction to axotomy is not perturbed by extended inflammation processes. Another advantage of the system is the accessibility of RGCs. Being in the more internal retinal layer, RGCs are directly exposed to the humor vitreus, the liquid filling the posterior chamber of the eye. Pharmaceutical treatments are easily injected into the eye and, diffusing in the vitreus, can reach all the RGCs. Last but not least, functional recovery can be easily monitored in the optic nerve; measurement of electrical activity in response to visual stimuli in CNS regions that receive inputs from the retina such as superior colliculus or visual cortex allows evaluation of the re-growth of ON fibers and the restoration of connections. All the experiments carried out so far indicate that the failure of regeneration in the ON, as in the majority of the CNS districts, is a multi-factorial phenomenon, involving three classes of negative events. 1) RGCs die after axotomy: in the adult rat, their number is reduced to a very small percentage in a few weeks after the lesion. 2) The majority of mature axotomised RGCs are not programmed to re-start the process of axonal elongation that they displayed in immature stages. 3) The optic nerve environment contains molecules many of them upregulated after the lesion that are inhibitory for axonal growth. This review, focused on experiments performed in the mammalian optic nerve, traces attempts made to overcome each of these three obstacles, and maps progress towards a combined therapeutic strategy.

Matrix metalloproteases and their inhibitors are produced by overlapping populations of activated astrocytes

Matrix metalloproteases (MMPs) and tissue inhibitors of metalloproteases (TIMPs) are involved in many cell migration phenomena and produced by many cell types, including neurons and glia. To assess their possible roles in brain injury and regeneration, we investigate their production by glial cells, after brain injury and in tissue culture, and we investigate whether they are capable of digesting known axon-inhibitory proteoglycans. To determine the action of MMPs, we incubated astrocyte conditioned medium with activated MMPs, then did western blots for several chondroitin sulphate proteoglycans. MMP-3 digested all five proteoglycans tested, whereas MMP-2 digested only two and MMP-9 none. To determine whether MMPs or TIMPs are produced by astrocytes in vitro, we tested both primary cultures and astrocyte cell lines by western blotting, and compared them with Schwann cells. All cultures produced at least some MMPs and TIMPs, with no obvious correlation with the ability of axons to grow on those cells. Both MMP-9 and TIMP-3 were regulated by various cytokines. To determine which cells produce MMPs and TIMPs after brain injury, we made lesions of adult rat cortex, and did immunohistochemistry. MMP-2 was seen to be induced in activated astrocytes through the whole thickness of the cortex but not deeper, but MMP-3 was not seen in the injured brain. TIMP-2 and TIMP-3 immunoreactivities were induced in activated astrocytes in deep cortex and the underlying white matter. In situ hybridisation confirmed induction of TIMP-2 in glia as well as neurons, but showed no expression of TIMP-4. These results show that both MMPs and TIMPs are produced by some astrocytes, but TIMP production is particularly strong, especially in deep cortex and white matter which is more inhibitory for axon regeneration. Conversely the MMPs produced may not be adequate to promote migration of cells and axons within the glial scar.

Relationship between sprouting axons, proteoglycans and glial cells following unilateral nigrostriatal axotomy in the adult rat

Proteoglycans may modulate axon growth in the intact and injured adult mammalian CNS. Here we investigate the distribution and time course of deposition of a range of proteoglycans between 4 and 14 days following unilateral axotomy of the nigrostriatal tract in anaesthetised adult rats. Immunolabelling using a variety of antibodies was used to examine the response of heparan sulphate proteoglycans, chondroitin sulphate proteoglycans and keratan sulphate proteoglycans. We observed that many proteoglycans became abundant between 1 and 2 weeks post-axotomy. Heparan sulphate proteoglycans were predominantly found within the lesion core (populated by blood vessels, amoeboid macrophages and meningeal fibroblasts) whereas chondroitin sulphate proteoglycans and keratan sulphate proteoglycans were predominantly found in the lesion surround (populated by reactive astrocytes, activated microglia and adult precursor cells). Immunolabelling indicated that cut dopaminergic nigral axons sprouted prolifically within the lesion core but rarely grew into the lesion surround. We conclude that sprouting of cut dopaminergic nigral axons may be supported by heparan sulphate proteoglycans but restricted by chondroitin sulphate proteoglycans and keratan sulphate proteoglycans.

Reduction in CNS scar formation without concomitant increase in axon regeneration following treatment of adult rat brain with a combination of antibodies to TGFbeta1 and beta2

In this study we investigated whether CNS axons regenerate following attenuation of scar formation using a combination of antibodies against two isoforms of transforming growth factor beta (TGFbeta). Anaesthetized adult rats were given unilateral mechanical lesions of the nigrostriatal tract. Implantation of transcranial cannulae allowed wounds to be treated with a combination of antibodies against TGFbeta1 and TGFbeta2 once daily for 10 days postaxotomy. Eleven days post-transection brains from animals under terminal anaesthesia were recovered for histological evaluation. Gliosis, inflammation and the response of dopaminergic nigral axons were assessed by immunolabelling. Treatment with antibodies against TGFbeta1 and TGFbeta2 attenuated (but did not abolish) the response of glial fibrillary acidic protein (GFAP)-immunoreactive astrocytes and of NG2-immunoreactive glia but did not attenuate the response of CR3-immunoreactive microglia and macrophages. However, this reduction in scar formation was not accompanied by growth of cut dopaminergic nigral axons. We conclude that treatment of injured adult rat brain with a combination of antibodies against TGFbeta1 and TGFbeta2 results in a reduction of scar formation but that this is not sufficient to enhance spontaneous long distance CNS axon regeneration.