Synergistic effects of brain-derived neurotrophic factor and chondroitinase ABC on retinal fiber sprouting after denervation of the superior colliculus in adult rats

Semaphorin 3A-Glycosaminoglycans Interaction as Therapeutic Target for Axonal Regeneration

Semaphorin 3A (Sema3A) is a cell-secreted protein that participates in the axonal guidance pathways. Sema3A acts as a canonical repulsive axon guidance molecule, inhibiting CNS regenerative axonal growth and propagation. Therefore, interfering with Sema3A signaling is proposed as a therapeutic target for achieving functional recovery after CNS injuries. It has been shown that Sema3A adheres to the proteoglycan component of the extracellular matrix (ECM) and selectively binds to heparin and chondroitin sulfate-E (CS-E) glycosaminoglycans (GAGs). We hypothesize that the biologically relevant interaction between Sema3A and GAGs takes place at Sema3A C-terminal polybasic region (SCT). The aims of this study were to characterize the interaction of the whole Sema3A C-terminal polybasic region (Sema3A 725–771) with GAGs and to investigate the disruption of this interaction by small molecules. Recombinant Sema3A basic domain was produced and we used a combination of biophysical techniques (NMR, SPR, and heparin affinity chromatography) to gain insight into the interaction of the Sema3A C-terminal domain with GAGs. The results demonstrate that SCT is an intrinsically disordered region, which confirms that SCT binds to GAGs and helps to identify the specific residues involved in the interaction. NMR studies, supported by molecular dynamics simulations, show that a new peptoid molecule (CSIC02) may disrupt the interaction between SCT and heparin. Our structural study paves the way toward the design of new molecules targeting these protein–GAG interactions with potential therapeutic applications.

Substrate Specificity and Biochemical Characteristics of an Engineered Mammalian Chondroitinase ABC

Chondroitin sulfate proteoglycans inhibit regeneration, neuroprotection, and plasticity following spinal cord injury. The development of a second-generation chondroitinase ABC enzyme, capable of being secreted from mammalian cells (mChABC), has facilitated the functional recovery of animals following severe spinal trauma. The genetically modified enzyme has been shown to efficiently break down the inhibitory extracellular matrix surrounding cells at the site of injury, while facilitating cellular integration and axonal growth. However, the activity profile of the enzyme in relation to the original bacterial chondroitinase (bChABC) has not been determined. Here, we characterize the activity profile of mChABC and compare it to bChABC, both enzymes having been maintained under physiologically relevant conditions for the duration of the experiment. We show that this genetically modified enzyme can be secreted reliably and robustly in high yields from a mammalian cell line. The modifications made to the cDNA of the enzyme have not altered the functional activity of mChABC compared to bChABC, ensuring that it has optimal activity on chondroitin sulfate-A, with an optimal pH at 8.0 and temperature at 37 °C. However, mChABC shows superior thermostability compared to bChABC, ensuring that the recombinant enzyme operates with enhanced activity over a variety of physiologically relevant substrates and temperatures compared to the widely used bacterial alternative without substantially altering its kinetic output. The determination that mChABC can function with greater robustness under physiological conditions than bChABC is an important step in the further development of this auspicious treatment strategy toward a clinical application.

Combination of stem cells from deciduous teeth and electroacupuncture for therapy in dogs with chronic spinal cord injury: A pilot study

Spinal cord injury (SCI) is a serious condition that causes profound economic and emotional impact in human patients and companion animal owners. It has been shown that the neurogenic effects of the stem cells are enhanced when combined with electroacupuncture (EA) in rodent models of SCI. To determine the safety and feasibility of combining transplantation of allogenic stem cells derived from canine exfoliated deciduous teeth (SCED) and EA in dogs with chronic spinal cord injury a canine pilot clinical study was conducted. A total of 16 individuals ranging from 5 to 11 years at 3 to 18 months of injury were investigated and randomly assigned to 4 experimental groups (SCED, EA, SCED + EA, control). Mild neurological and functional improvements were seen in all 4 groups. There was no clinical progression or mortality of the cases occurred in a follow up of 7 months after procedure. The study shows that SCED transplantation and electroacupuncture were feasible, safe and potentially beneficial. However Long-term patient monitoring is necessary to rule out any delayed side effects and assess any further improvements.

Plasticity Induced Recovery of Breathing Occurs at Chronic Stages after Cervical Contusion

Severe midcervical contusion injury causes profound deficits throughout the respiratory motor system that last from acute to chronic time points post-injury. We use chondroitinase ABC (ChABC) to digest chondroitin sulphate proteoglycans within the extracellular matrix (ECM) surrounding the respiratory system at both acute and chronic time points post-injury to explore whether augmentation of plasticity can recover normal motor function. We demonstrate that, regardless of time post-injury or treatment application, the lesion cavity remains consistent, showing little regeneration or neuroprotection within our model. Through electromyography (EMG) recordings of multiple inspiratory muscles, however, we show that application of the enzyme at chronic time points post-injury initiates the recovery of normal breathing in previously paralyzed respiratory muscles. This reduced the need for compensatory activity throughout the motor system. Application of ChABC at acute time points recovered only modest amounts of respiratory function. To further understand this effect, we assessed the anatomical mechanism of this recovery. Increased EMG activity in previously paralyzed muscles was brought about by activation of spared bulbospinal pathways through the site of injury and/or sprouting of spared serotonergic fibers from the contralateral side of the cord. Accordingly, we demonstrate that alterations to the ECM and augmentation of plasticity at chronic time points post-cervical contusion can cause functional recovery of the respiratory motor system and reveal mechanistic evidence of the pathways that govern this effect.

The Biology of Regeneration Failure and Success After Spinal Cord Injury

Since no approved therapies to restore mobility and sensation following spinal cord injury (SCI) currently exist, a better understanding of the cellular and molecular mechanisms following SCI that compromise regeneration or neuroplasticity is needed to develop new strategies to promote axonal regrowth and restore function. Physical trauma to the spinal cord results in vascular disruption that, in turn, causes blood-spinal cord barrier rupture leading to hemorrhage and ischemia, followed by rampant local cell death. As subsequent edema and inflammation occur, neuronal and glial necrosis and apoptosis spread well beyond the initial site of impact, ultimately resolving into a cavity surrounded by glial/fibrotic scarring. The glial scar, which stabilizes the spread of secondary injury, also acts as a chronic, physical, and chemo-entrapping barrier that prevents axonal regeneration. Understanding the formative events in glial scarring helps guide strategies towards the development of potential therapies to enhance axon regeneration and functional recovery at both acute and chronic stages following SCI. This review will also discuss the perineuronal net and how chondroitin sulfate proteoglycans (CSPGs) deposited in both the glial scar and net impede axonal outgrowth at the level of the growth cone. We will end the review with a summary of current CSPG-targeting strategies that help to foster axonal regeneration, neuroplasticity/sprouting, and functional recovery following SCI.

Substance P and pain chronicity

Substance P (SP) is a highly conserved member of the tachykinin peptide family that is widely expressed throughout the animal kingdom. The numerous members of the tachykinin peptide family are involved in a multitude of neuronal signaling pathways, mediating sensations and emotional responses (Steinhoff et al. in Physiol Rev 94:265–301, 2014). In contrast to receptors for classical transmitters, such as glutamate (Parsons et al. in Handb Exp Pharmacol 249–303, 2005), only a minority of neurons in certain brain areas express neurokinin receptors (NKRs) (Mantyh in J Clin Psychiatry 63:6–10, 2002). SP is also expressed by a variety of non-neuronal cell types such as microglia, as well as immune cells (Mashaghi et al. in Cell Mol Life Sci 73:4249–4264, 2016). SP is an 11-amino acid neuropeptide that preferentially activates the neurokinin-1 receptor (NK1R). It transmits nociceptive signals via primary afferent fibers to spinal and brainstem second-order neurons (Cao et al. in Nature 392:390–394, 1998). Compounds that inhibit SP’s action are being investigated as potential drugs to relieve pain. More recently, SP and NKR have gained attention for their role in complex psychiatric processes. It is a key goal in the field of pain research to understand mechanisms involved in the transition between acute pain and chronic pain. The influence of emotional and cognitive inputs and feedbacks from different brain areas makes pain not only a perception but an experience (Zieglgänsberger et al. in CNS Spectr 10:298–308, 2005; Trenkwaldner et al. Sleep Med 31:78–85, 2017). This review focuses on functional neuronal plasticity in spinal dorsal horn neurons as a major relay for nociceptive information.

Chondroitinase ABC Treatment Enhances Synaptogenesis between Transplant and Host Neurons in Model of Retinal Degeneration

Although recent studies revealed chondroitinase ABC (ChABC), an enzyme that degrades chondroitin sulfate proteoglycans, promotes CNS regeneration in vivo, the usefulness of its application for transplantation is not clear. We investigated if treatment with ChABC can promote synapse formation between graft and host neurons following retinal transplantation. Dissociated retinal cells were prepared from neonatal Nrl-GFP transgenic mice in which rod photoreceptors and their progenitor cells are labeled with GFP. Each cell suspension with or without ChABC (Nrl/ChABC group and Nrl group, respectively) was injected subretinally into the eyes of mice following chemically induced photoreceptor degeneration. The survival and functional integration of the transplanted photoreceptors were examined by histologically and electrophysio-logically. Up to 4 weeks after transplantation, almost all the grafted GFP+ photoreceptor cells were widely distributed at the outer margin of the host retina where the photoreceptor layer was located originally. In the Nrl/ChABC group, 33.6% of the GFP+ photoreceptors elaborated neurites horizontally or vertically, and 4.6% elaborated neurites toward the retina. These neurites extended over the glial seal at the graft–host interface, and established synaptic contacts with neurons in the host retina as determined by confocal microscopy and three-dimensional analysis. Although 30.7% cells (p = 0.68) elaborated neurites in the Nrl group, only 1.2% cells (p < 0.05) projected neurites towards the host tissue and synaptic contacts were rare. Our results illustrate the potential utility of ChABC for enhancing synaptogenesis between transplanted neurons and host retina.

Nogo-A in the visual system development and in ocular diseases

Nogo-A is a potent myelin-associated inhibitor for neuronal growth and plasticity in the central nervous system (CNS). Its effects are mediated by the activation of specific receptors that intracellularly control cytoskeleton rearrangements, protein synthesis and gene expression. Moreover, Nogo-A has been involved in the development of the visual system and in a variety of neurodegenerative diseases and injury processes that can alter its function. For example, Nogo-A was shown to influence optic nerve myelinogenesis, the formation and maturation of retinal axon projections, and retinal angiogenesis. In adult animals, the inactivation of Nogo-A exerted remarkable effects on visual plasticity. Relieving Nogo-A-induced inhibition increased axonal sprouting after optic nerve lesion and axonal rewiring in the visual cortex of intact adult mice. This review aims at presenting our current knowledge on the role of Nogo-A in the visual system and to discuss how its therapeutic targeting may promote visual improvement in ophthalmic diseases.

Combined chondroitinase and KLF7 expression reduce net retraction of sensory and CST axons from sites of spinal injury

Axon regeneration in the central nervous system is limited both by inhibitory extracellular cues and by an intrinsically low capacity for axon growth in some CNS populations. Chondroitin sulfate proteoglycans (CSPGs) are well-studied inhibitors of axon growth in the CNS, and degradation of CSPGs by chondroitinase has been shown to improve the extension of injured axons. Alternatively, axon growth can be improved by targeting the neuron-intrinsic growth capacity through forced expression of regeneration-associated transcription factors. For example, a transcriptionally active chimera of Krüppel-like Factor 7 (KLF7) and a VP16 domain improves axon growth when expressed in corticospinal tract neurons. Here we tested the hypothesis that combined expression of chondroitinase and VP16-KLF7 would lead to further improvements in axon growth after spinal injury. Chondroitinase was expressed by viral transduction of cells in the spinal cord, while VP16-KLF7 was virally expressed in sensory neurons of the dorsal root ganglia or corticospinal tract (CST) neurons. After transection of the dorsal columns, both chondroitinase and VP16-KLF7 increased the proximity of severed sensory axons to the injury site. Similarly, after complete crush injuries, VP16-KLF7 expression increased the approach of CST axons to the injury site. In neither paradigm however, did single or combined treatment with chondroitinase or VP16-KLF7 enable regenerative growth distal to the injury. These results substantiate a role for CSPG inhibition and low KLF7 activity in determining the net retraction of axons from sites of spinal injury, while suggesting that additional factors act to limit a full regenerative response.

Neuroprotective and restorative effects of the brain-derived neurotrophic factor in retinal diseases

Brain-derived neurotrophic factor (BDNF) is a neurotrophin proposed to be implicated in ameliorating the course of some neurodegenerative disorders. Given the fact that retina is considered as an out-pouching of the central nervous system, its related diseases have long been suggested to receive protective influence from this signaling molecule. The role of BDNF in retinal neurorestoration, neuroprotection and oxidative stress has extensively been tested over the past two decades. Nonetheless, almost the entire related literature root in animal studies and clinical research on this topic is lacking. Although much of the evidence have validated the protective properties of BDNF against various retinal cell diseases, bringing such insights into clinical context would depend on further well-designed research. The present review is an attempt to categorize and discuss the available evidence with regard to the BDNF and retinal diseases.

Retinal lesions induce fast intrinsic cortical plasticity in adult mouse visual system

Neuronal activity plays an important role in the development and structural-functional maintenance of the brain as well as in its life-long plastic response to changes in sensory stimulation. We characterized the impact of unilateral 15° laser lesions in the temporal lower visual field of the retina, on visually driven neuronal activity in the afferent visual pathway of adult mice using in situ hybridization for the activity reporter gene zif268. In the first days post-lesion, we detected a discrete zone of reduced zif268 expression in the contralateral hemisphere, spanning the border between the monocular segment of the primary visual cortex (V1) with extrastriate visual area V2M. We could not detect a clear lesion projection zone (LPZ) in areas lateral to V1 whereas medial to V2M, agranular and granular retrosplenial cortex showed decreased zif268 levels over their full extent. All affected areas displayed a return to normal zif268 levels, and this was faster in higher order visual areas than in V1. The lesion did, however, induce a permanent LPZ in the retinorecipient layers of the superior colliculus. We identified a retinotopy-based intrinsic capacity of adult mouse visual cortex to recover from restricted vision loss, with recovery speed reflecting the areal cortical magnification factor. Our observations predict incomplete visual field representations for areas lateral to V1 vs. lack of retinotopic organization for areas medial to V2M. The validation of this mouse model paves the way for future interrogations of cortical region- and cell-type-specific contributions to functional recovery, up to microcircuit level.

The hyaluronan and proteoglycan link proteins: Organizers of the brain extracellular matrix and key molecules for neuronal function and plasticity

The hyaluronan and proteoglycanbinding link protein (Hapln) is a key molecule in the formation and control of hyaluronan-based condensed perineuronal matrix in the adult brain. This review summarizes the recent advances in understanding the role of Haplns in the formation and control of two distinct types of perineuronal matrices, one for "classical" PNN and the other for the specialized extracellular matrix (ECM) at the node of Ranvier in the central nervous system (CNS). We introduce the structural components of each ECM organization including the basic concept of supramolecular structure named "HLT model". We furthermore summarize the developmental and physiological role of perineuronal ECMs from the studies of Haplns and related molecules. Finally, we also discuss the potential mechanism modulating PNNs in the adult CNS. This layer of organized matrices may exert a direct effect via core protein or sugar moiety from the structure or by acting as a binding site for biologically active molecules, which are important for neuronal plasticity and saltatory conduction.

Cells transplanted onto the surface of the glial scar reveal hidden potential for functional neural regeneration

Cell transplantation therapy has long been investigated as a therapeutic intervention for neurodegenerative disorders, including spinal cord injury, Parkinson's disease, and amyotrophic lateral sclerosis. Indeed, patients have high hopes for a cell-based therapy. However, there are numerous practical challenges for clinical translation. One major problem is that only very low numbers of donor cells survive and achieve functional integration into the host. Glial scar tissue in chronic neurodegenerative disorders strongly inhibits regeneration, and this inhibition must be overcome to accomplish successful cell transplantation. Intraneural cell transplantation is considered to be the best way to deliver cells to the host. We questioned this view with experiments in vivo on a rat glial scar model of the auditory system. Our results show that intraneural transplantation to the auditory nerve, preceded by chondroitinase ABC (ChABC)-treatment, is ineffective. There is no functional recovery, and almost all transplanted cells die within a few weeks. However, when donor cells are placed on the surface of a ChABC-treated gliotic auditory nerve, they autonomously migrate into it and recapitulate glia- and neuron-guided cell migration modes to repair the auditory pathway and recover auditory function. Surface transplantation may thus pave the way for improved functional integration of donor cells into host tissue, providing a less invasive approach to rescue clinically important neural tracts.

Ocular hypertension results in retinotopic alterations in the visual cortex of adult mice

PURPOSE

Glaucoma is a group of optic neuropathies characterized by the loss of retinal ganglion cells (RGCs). Since ocular hypertension (OHT) is a main risk factor, current therapies are predominantly based on lowering eye pressure. However, a subset of treated patients continues to lose vision. More research into pathological mechanisms underlying glaucoma is therefore warranted in order to develop novel therapeutic strategies. In this study we investigated the impact of OHT from eye to brain in mice.

METHODS

Monocular hypertension (mOHT) was induced in CD-1 mice by laser photocoagulation (LP) of the perilimbal and episcleral veins. The impact on the retina and its main direct target area, the superficial superior colliculus (sSC), was examined via immunostainings for Brn3a, VGluT2 and GFAP. Alterations in neuronal activity in V1 and extrastriate areas V2L and V2M were assessed using in situ hybridization for the activity reporter gene zif268.

RESULTS

Transient mOHT resulted in diffuse and sectorial RGC degeneration. In the sSC contralateral to the OHT eye, a decrease in VGluT2 immunopositive synaptic connections was detected one week post LP, which appeared to be retinotopically linked to the sectorial RGC degeneration patterns. In parallel, hypoactivity was discerned in contralateral retinotopic projection zones in V1 and V2. Despite complete cortical reactivation 4 weeks post LP, in the sSC no evidence for recovery of RGC synapse density was found and also the concomitant inflammation was not completely resolved. Nevertheless, sSC neurons appeared healthy upon histological inspection and subsequent analysis of cell density revealed no differences between the ipsi- and contralateral sSC.

CONCLUSION

In addition to RGC death, OHT induces loss of synaptic connections and neuronal activity in the visual pathway and is accompanied by an extensive immune response. Our findings stress the importance of looking beyond the eye and including the whole visual system in glaucoma research.

Possible roles of COX-1 in learning and memory impairment induced by traumatic brain injury in mice

People who suffer from traumatic brain injury (TBI) often experience cognitive deficits in spatial reference and working memory. The possible roles of cyclooxygenase-1 (COX-1) in learning and memory impairment in mice with TBI are far from well known. Adult mice subjected to TBI were treated with the COX-1 selective inhibitor SC560. Performance in the open field and on the beam walk was then used to assess motor and behavioral function 1, 3, 7, 14, and 21 days following injury. Acquisition of spatial learning and memory retention was assessed using the Morris water maze on day 15 post-TBI. The expressions of COX-1, prostaglandin E2 (PGE2), interleukin (IL)-6, brain-derived neurotrophic factor (BDNF), platelet-derived growth factor BB (PDGF-BB), synapsin-I, and synaptophysin were detected in TBI mice. Administration of SC560 improved performance of beam walk tasks as well as spatial learning and memory after TBI. SC560 also reduced expressions of inflammatory markers IL-6 and PGE2, and reversed the expressions of COX-1, BDNF, PDGF-BB, synapsin-I, and synaptophysin in TBI mice. The present findings demonstrated that COX-1 might play an important role in cognitive deficits after TBI and that selective COX-1 inhibition should be further investigated as a potential therapeutic approach for TBI.

Cortical reorganization after spinal cord injury: always for good?

Plasticity constitutes the basis of behavioral changes as a result of experience. It refers to neural network shaping and re-shaping at the global level and to synaptic contacts remodeling at the local level, either during learning or memory encoding, or as a result of acute or chronic pathological conditions. 'Plastic' brain reorganization after central nervous system lesions has a pivotal role in the recovery and rehabilitation of sensory and motor dysfunction, but can also be "maladaptive". Moreover, it is clear that brain reorganization is not a "static" phenomenon but rather a very dynamic process. Spinal cord injury immediately initiates a change in brain state and starts cortical reorganization. In the long term, the impact of injury - with or without accompanying therapy - on the brain is a complex balance between supraspinal reorganization and spinal recovery. The degree of cortical reorganization after spinal cord injury is highly variable, and can range from no reorganization (i.e. "silencing") to massive cortical remapping. This variability critically depends on the species, the age of the animal when the injury occurs, the time after the injury has occurred, and the behavioral activity and possible therapy regimes after the injury. We will briefly discuss these dependencies, trying to highlight their translational value. Overall, it is not only necessary to better understand how the brain can reorganize after injury with or without therapy, it is also necessary to clarify when and why brain reorganization can be either "good" or "bad" in terms of its clinical consequences. This information is critical in order to develop and optimize cost-effective therapies to maximize functional recovery while minimizing maladaptive states after spinal cord injury.

A robotic system for quantitative assessment and poststroke training of forelimb retraction in mice

BACKGROUND

Neurorehabilitation protocols based on the use of robotic devices have recently shown to provide promising clinical results. However, their efficacy is still limited because of the poor comprehension of the mechanisms at the basis of functional enhancements.

OBJECTIVE

To increase basic understanding of robot-mediated neurorehabilitation by performing experiments on a rodent model of stroke.

METHODS

Mice were trained to pull back a handle on a robotic platform and their performances in the task were evaluated before and after a focal cortical ischemic stroke. The platform was designed for the quantitative assessment of forelimb function via a series of parameters (time needed to complete the task, t-target; average force; number of sub-movements).

RESULTS

The animals rapidly learned the retraction task and reached asymptotic performance by the fifth session of training. Within 2 to 6 days after a small, endothelin-1-induced lesion in the caudal forelimb area, mice showed an increase in t-target and number of sub-movements and a corresponding decrease in the average force exerted. These parameters returned to baseline, pre-lesion values with continued platform training (10-14 days after stroke).

CONCLUSIONS

These results highlight the utility of the devised platform for characterizing post-infarct deficits and improvements of forelimb performance. Further research is warranted to widen the understanding of device-dependent rehabilitation effects.

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.

Chondroitinase enhances cortical map plasticity and increases functionally active sprouting axons after brain injury

The beneficial effect of interventions with chondroitinase ABC enzyme to reduce axon growth-inhibitory chondroitin sulphate side chains after central nervous system injuries has been mainly attributed to enhanced axonal sprouting. After traumatic brain injury (TBI), it is unknown whether newly sprouting axons that occur as a result of interventional strategies are able to functionally contribute to existing circuitry, and it is uncertain whether maladaptive sprouting occurs to increase the well-known risk for seizure activity after TBI. Here, we show that after a controlled cortical impact injury in rats, chondroitinase infusion into injured cortex at 30 min and 3 days reduced c-Fos⁺ cell staining resulting from the injury alone at 1 week postinjury, indicating that at baseline, abnormal spontaneous activity is likely to be reduced, not increased, with this type of intervention. c-Fos⁺ cell staining elicited by neural activity from stimulation of the affected forelimb 1 week after injury was significantly enhanced by chondroitinase, indicating a widespread effect on cortical map plasticity. Underlying this map plasticity was a larger contribution of neuronal, rather than glial cells and an absence of c-Fos⁺ cells surrounded by perineuronal nets that were normally present in stimulated naïve rats. After injury, chondroitin sulfate proteoglycan digestion produced the expected increase in growth-associated protein 43-positive axons and perikarya, of which a significantly greater number were double labeled for c-Fos after intervention with chondroitinase, compared to vehicle. These data indicate that chondroitinase produces significant gains in cortical map plasticity after TBI, and that either axonal sprouting and/or changes in perineuronal nets may underlie this effect. Chondroitinase dampens, rather than increases nonspecific c-Fos activity after brain injury, and induction of axonal sprouting is not maladaptive because greater numbers are functionally active and provide a significant contribution to forelimb circuitry after brain injury.

Comparison of sensory neuron growth cone and filopodial responses to structurally diverse aggrecan variants, in vitro

Following spinal cord injury, a regenerating neurite encounters a glial scar enriched in chondroitin sulfate proteoglycans (CSPGs), which presents a major barrier. There are two points at which a neurite makes contact with glial scar CSPGs: initially, filopodia surrounding the growth cone extend and make contact with CSPGs, then the peripheral domain of the entire growth cone makes CSPG contact. Aggrecan is a CSPG commonly used to model the effect CSPGs have on elongating or regenerating neurites. In this study, we investigated filopodia and growth cone responses to contact with structurally diverse aggrecan variants using the common stripe assay. Using time-lapse imaging with 15-s intervals, we measured growth cone area, growth cone width, growth cone length, filopodia number, total filopodia length, and the length of the longest filopodia following contact with aggrecan. Responses were measured after both filopodia and growth cone contact with five different preparations of aggrecan: two forms of aggrecan derived from bovine articular cartilage (purified and prepared using different techniques), recombinant aggrecan lacking chondroitin sulfate side chains (produced in CHO-745 cells) and two additional recombinant aggrecan preparations with varying lengths of chondroitin sulfate side chains (produced in CHO-K1 and COS-7 cells). Responses in filopodia and growth cone behavior differed between the structurally diverse aggrecan variants. Mutant CHO-745 aggrecan (lacking chondroitin sulfate chains) permitted extensive growth across the PG stripe. Filopodia contact with the CHO-745 aggrecan caused a significant increase in growth cone width and filopodia length (112.7% ± 4.9 and 150.9% ± 7.2 respectively, p<0.05), and subsequently upon growth cone contact, growth cone width remained elevated along with a reduction in filopodia number (121.9% ± 4.2; 72.39% ± 6.4, p<0.05). COS-7 derived aggrecan inhibited neurite outgrowth following growth cone contact. Filopodia contact produced an increase in growth cone area and width (126.5% ± 8.1; 150.3% ± 13.31, p<0.001), and while these parameters returned to baseline upon growth cone contact, a reduction in filopodia number and length was observed (73.94% ± 5.8, 75.3% ± 6.2, p<0.05). CHO-K1 derived aggrecan inhibited neurite outgrowth following filopodia contact, and caused an increase in growth cone area and length (157.6% ± 6.2; 117.0% ± 2.8, p<0.001). Interestingly, the two bovine articular cartilage aggrecan preparations differed in their effects on neurite outgrowth. The proprietary aggrecan (BA I, Sigma-Aldrich) inhibited neurites at the point of growth cone contact, while our chemically purified aggrecan (BA II) inhibited neurite outgrowth at the point of filopodia contact. BA I caused a reduction in growth cone width following filopodia contact (91.7% ± 2.5, p<0.05). Upon growth cone contact, there was a further reduction in growth cone width and area (66.4% ± 2.2; 75.6% ± 2.9; p<0.05), as well as reductions in filopodia number, total length, and max length (75.9% ± 5.7, p<0.05; 68.8% ± 6.0; 69.6% ± 3.5, p<0.001). Upon filopodia contact, BA II caused a significant increase in growth cone area, and reductions in filopodia number and total filopodia length (115.9% ± 5.4, p<0.05; 72.5% ± 2.7; 77.7% ± 3.2, p<0.001). In addition, filopodia contact with BA I caused a significant reduction in growth cone velocity (38.6 nm/s ± 1.3 before contact, 17.1 nm/s ± 3.6 after contact). These data showed that neuron morphology and behavior are differentially dependent upon aggrecan structure. Furthermore, the behavioral changes associated with the approaching growth cone may be predictive of inhibition or growth.

Creb is modulated in the mouse superior colliculus in developmental and experimentally-induced models of plasticity

In the central nervous system long-term plastic processes need the activation of specific gene expression programs and the synthesis of new protein in order to occur. A transcription factor fundamental for several plasticity mechanisms in various CNS areas is the cAMP response element-binding protein, CREB. This factor is activated through phosphorylation at its Serine 133 residue by multiple signaling pathways. Little is known about CREB role in the superior colliculus, a midbrain area considered an experimentally useful model for the study of neuronal plasticity processes. In the present work we studied by Western blot analysis the modulation of CREB expression and activation in the mouse superior colliculus in three models of neuronal plasticity: (1) developmental plasticity; (2) lesion-induced plasticity; (3) and fluoxetine-induced restored plasticity. We used an antibody that detects endogenous level of the total CREB protein (anti-TCREB) to identify possible modulations at CREB expression level, and a second antibody (anti-PCREB) that detects endogenous level of CREB only when it is phosphorylated at Ser133, to identify modifications of CREB activation state. The results showed that: (1) the expression and activation of CREB increase during the development of the superior colliculus in temporal correlation with the plastic process of refinement of retino-collicular projections; (2) the activation of CREB is induced by a monocular lesion performed during the critical period for plasticity in young animals but not when performed in less plastic juvenile mice; (3) the expression and activation of CREB increase in adult animals treated with fluoxetine, known to restore high levels of plasticity in adult animals. These results suggest that CREB transcription factor plays a fundamental role in plasticity processes also at the level of the mouse superior colliculus.

Chondroitinase ABC promotes compensatory sprouting of the intact corticospinal tract and recovery of forelimb function following unilateral pyramidotomy in adult mice

Chondroitin sulphate proteoglycans (CSPGs) are extracellular matrix molecules whose inhibitory activity is attenuated by the enzyme chondroitinase ABC (ChABC). Here we assess whether CSPG degradation can promote compensatory sprouting of the intact corticospinal tract (CST) following unilateral injury and restore function to the denervated forelimb. Adult C57BL/6 mice underwent unilateral pyramidotomy and treatment with either ChABC or a vehicle control. Significant impairments in forepaw symmetry were observed following pyramidotomy, with injured mice preferentially using their intact paw during spontaneous vertical exploration of a cylinder. No recovery on this task was observed in vehicle-treated mice. However, ChABC-treated mice showed a marked recovery of function, with forelimb symmetry fully restored by 5 weeks post-injury. Functional recovery was associated with robust sprouting of the uninjured CST, with numerous axons observed crossing the midline in the brainstem and spinal cord and terminating in denervated grey matter. CST fibres in the denervated side of the spinal cord following ChABC treatment were closely associated with the synaptic marker vGlut1. Immunohistochemical assessment of chondroitin-4-sulphate revealed that CSPGs were heavily digested around lamina X, alongside midline crossing axons and in grey matter regions where sprouting axons and reduced peri-neuronal net staining was observed. Thus, we demonstrate that CSPG degradation promotes midline crossing and reinnervation of denervated target regions by intact CST axons and leads to restored function in the denervated forepaw. Enhancing compensatory sprouting using ChABC provides a route to restore function that could be applied to disorders such as spinal cord injury and stroke.

Conditional Sox9 ablation reduces chondroitin sulfate proteoglycan levels and improves motor function following spinal cord injury

Chondroitin sulfate proteoglycans (CSPGs) found in perineuronal nets and in the glial scar after spinal cord injury have been shown to inhibit axonal growth and plasticity. Since we have previously identified SOX9 as a transcription factor that upregulates the expression of a battery of genes associated with glial scar formation in primary astrocyte cultures, we predicted that conditional Sox9 ablation would result in reduced CSPG expression after spinal cord injury and that this would lead to increased neuroplasticity and improved locomotor recovery. Control and Sox9 conditional knock-out mice were subject to a 70 kdyne contusion spinal cord injury at thoracic level 9. One week after injury, Sox9 conditional knock-out mice expressed reduced levels of CSPG biosynthetic enzymes (Xt-1 and C4st), CSPG core proteins (brevican, neurocan, and aggrecan), collagens 2a1 and 4a1, and Gfap, a marker of astrocyte activation, in the injured spinal cord compared with controls. These changes in gene expression were accompanied by improved hind limb function and locomotor recovery as evaluated by the Basso Mouse Scale (BMS) and rodent activity boxes. Histological assessments confirmed reduced CSPG deposition and collagenous scarring at the lesion of Sox9 conditional knock-out mice, and demonstrated increased neurofilament-positive fibers in the lesion penumbra and increased serotonin immunoreactivity caudal to the site of injury. These results suggest that SOX9 inhibition is a potential strategy for the treatment of SCI.

Traumatic brain injury in pediatric patients: evidence for the effectiveness of decompressive surgery

Traumatic brain injury (TBI) is the current leading cause of death in children over 1 year of age. Adequate management and care of pediatric patients is critical to ensure the best functional outcome in this population. In their controversial trial, Cooper et al. concluded that decompressive craniectomy following TBI did not improve clinical outcome of the analyzed adult population. While the study did not target pediatric populations, the results do raise important and timely clinical questions regarding the effectiveness of decompressive surgery in pediatric patients. There is still a paucity of evidence regarding the effectiveness of this therapy in a pediatric population, and there is an especially noticeable knowledge gap surrounding age-stratified interventions in pediatric trauma. The purposes of this review are to first explore the anatomical variations between pediatric and adult populations in the setting of TBI. Second, the authors assess how these differences between adult and pediatric populations could translate into differences in the impact of decompressive surgery following TBI.

Botulinum neurotoxin A impairs neurotransmission following retrograde transynaptic transport

The widely used botulinum neurotoxin A (BoNT/A) blocks neurotransmission via cleavage of the synaptic protein SNAP-25 (synaptosomal-associated protein of 25 kDa). Recent evidence demonstrating long-distance propagation of SNAP-25 proteolysis has challenged the idea that BoNT/A remains localized to the injection site. However, the extent to which distant neuronal networks are impacted by BoNT/A retrograde trafficking remains unknown. Importantly, no studies have addressed whether SNAP-25 cleavage translates into structural and functional changes in distant intoxicated synapses. Here we show that the BoNT/A injections into the adult rat optic tectum result in SNAP-25 cleavage in retinal neurons two synapses away from the injection site, such as rod bipolar cells and photoreceptors. Retinal endings displaying cleaved SNAP-25 were enlarged and contained an abnormally high number of synaptic vesicles, indicating impaired exocytosis. Tectal injection of BoNT/A in rat pups resulted in appearance of truncated-SNAP-25 in cholinergic amacrine cells. Functional imaging with calcium indicators showed a clear reduction in cholinergic-driven wave activity, demonstrating impairments in neurotransmission. These data provide the first evidence for functional effects of the retrograde trafficking of BoNT/A, and open the possibility of using BoNT/A fragments as drug delivery vehicles targeting the central nervous system.

Potential treatment strategies for enhancing neuroplasticity and regeneration after ischemic stroke

Strokes are a major cause of death and result in a drastic reduction in quality of life. Novel therapeutic strategies for patients suffering from stroke are thus required. Two possible strategies can be proposed for treating ischemic stroke: enhancing neuroplasticity, allowing the surviving neuronal cells to compensate for stroke-related impairment through brain reorganization, sprouting and rewiring of neuronal cells, or regeneration of neuronal cells, including enhancement of intrinsic neurogenesis and stem cell transplantation therapy with neural stem cells, embryonic stem cells or induced pluripotent stem cells. Endogenous neurogenesis or transplanted neural stem cells, embryonic stem cells or induced pluripotent stem cell-derived cells are able to not only supply newborn neurons integrated into a damaged neuronal network, but also produce growth factors into the recovering brains. These secretory factors enhance sprouting and angiogenesis and may be important in neuroplasticity and recovery in the poststroke brain.

The perineuronal net and the control of CNS plasticity

Perineuronal nets (PNNs) are reticular structures that surround the cell body of many neurones, and extend along their dendrites. They are considered to be a specialized extracellular matrix in the central nervous system (CNS). PNN formation is first detected relatively late in development, as the mature synaptic circuitry of the CNS is established and stabilized. Its unique distribution in different CNS regions, the timing of its establishment, and the changes it undergoes after injury all point toward diverse and important functions that it may be performing. The involvement of PNNs in neuronal plasticity has been extensively studied over recent years, with developmental, behavioural, and functional correlations. In this review, we will first briefly detail the structure and organization of PNNs, before focusing our discussion on their unique roles in neuronal development and plasticity. The PNN is an important regulator of CNS plasticity, both during development and into adulthood. Production of critical PNN components is often triggered by appropriate sensory experiences during early postnatal development. PNN deposition around neurones helps to stabilize the established neuronal connections, and to restrict the plastic changes due to future experiences within the CNS. Disruption of PNNs can reactivate plasticity in many CNSs, allowing activity-dependent changes to once again modify neuronal connections. The mechanisms through which PNNs restrict CNS plasticity remain unclear, although recent advances promise to shed additional light on this important subject.

Neurotrophic factors and the regeneration of adult retinal ganglion cell axons

The adult central nervous system (CNS) has only a limited capacity to regenerate axons after injury. This is due to a number of factors including the presence of extrinsic inhibitory factors that limit plasticity, lack of effective trophic support, and intrinsic changes in neuronal responsiveness. In this review, we describe the expression and role of neurotrophins in retinal ganglion cells (RGCs) during development and adulthood, and the receptors and miscellaneous signaling systems that influence axonal regeneration after injury. The impact of exogenous neurotrophic factors on adult RGCs injured at different sites in the visual pathway is described for several modes of delivery, including recombinant factors, viral vectors, cell transplantation, as well as combinatorial treatments involving other pharmacotherapeutic agents. Indirect, off-target effects of neurotrophic factors on RGC axonal regeneration are also considered. There remain unresolved issues relating to optimal delivery of neurotrophic factors, and we emphasize the need to develop safe, reliable methods for the regulation of exogenous supply of these factors to the injured CNS.

Oncomodulin affords limited regeneration to injured sensory axons in vitro and in vivo

Oncomodulin, an ~12 kDa Ca(2+)-binding protein secreted from activated macrophages, has been shown to promote axonal regeneration from retinal ganglion cells (RGCs) following optic nerve injury. However, to date, the axonal growth-promoting capacity of oncomodulin in other models of 'regenerative failure' has not been evaluated. We assessed the capability of preconditioning treatment with oncomodulin to promote sensory axonal regeneration in an in vitro spot model of regenerative failure, and across the dorsal root zone (DREZ) after root crush injury. Neither the direct exposure of adult rat DRGs to oncomodulin, nor preconditioning of DRGs by intraganglionic injection of oncomodulin, stimulated axonal outgrowth in the in vitro proteoglycan spot gradient assay. However, direct exposure of unconditioned DRGs to both oncomodulin and db-cAMP in vitro, as well as preconditioning of DRGs with the combined treatment in vivo, resulted in significant, albeit modest, neurite extension across the inhibitory proteoglycan barrier. We next quantified axon regeneration through the C8 DREZ in adult rats after oncomodulin and/or db-cAMP preconditioning and chondroitinase (ChABC) injection into the DREZ immediately following a root crush injury. Axonal regeneration across the DREZ was not observed in control animals, or after injection of ChABC-alone. Treatment with oncomodulin- or db-cAMP-alone resulted in extremely sparse regeneration. However, significant, but meager, sensory axon regeneration across the DREZ was observed using the oncomodulin/ db-cAMP combination (p<0.001), supporting findings from previous studies suggesting that cAMP is necessary for the growth-promoting effects of oncomodulin. Although our results support a role for oncomodulin in macrophage-induced axonal regeneration, the effects of oncomodulin/db-cAMP on sensory regeneration were extremely limited in comparison to previous studies in the same injury model using zymosan.

Training and anti-CSPG combination therapy for spinal cord injury

Combining different therapies is a promising strategy to promote spinal cord repair, by targeting axon plasticity and functional circuit reconnectivity. In particular, digestion of chondroitin sulphate proteoglycans at the site of the injury by the activity of the bacterial enzyme chondrotinase ABC, together with the development of intensive task specific motor rehabilitation has shown synergistic effects to promote behavioural recovery. This review describes the mechanisms by which chondroitinase ABC and motor rehabilitation promote neural plasticity and we discuss their additive and independent effects on promoting behavioural recovery.

Chondroitin sulphate proteoglycans: key modulators of spinal cord and brain plasticity

Chondroitin sulphate proteoglycans (CSPGs) are a family of inhibitory extracellular matrix molecules that are highly expressed during development, where they are involved in processes of pathfinding and guidance. CSPGs are present at lower levels in the mature CNS, but are highly concentrated in perineuronal nets where they play an important role in maintaining stability and restricting plasticity. Whilst important for maintaining stable connections, this can have an adverse effect following insult to the CNS, restricting the capacity for repair, where enhanced synapse formation leading to new connections could be functionally beneficial. CSPGs are also highly expressed at CNS injury sites, where they can restrict anatomical plasticity by inhibiting sprouting and reorganisation, curbing the extent to which spared systems may compensate for the loss function of injured pathways. Modification of CSPGs, usually involving enzymatic degradation of glycosaminoglycan chains from the CSPG molecule, has received much attention as a potential strategy for promoting repair following spinal cord and brain injury. Pre-clinical studies in animal models have demonstrated a number of reparative effects of CSPG modification, which are often associated with functional recovery. Here we discuss the potential of CSPG modification to stimulate restorative plasticity after injury, reviewing evidence from studies in the brain, the spinal cord and the periphery.

Immature astrocytes promote CNS axonal regeneration when combined with chondroitinase ABC

Regeneration of injured adult CNS axons is inhibited by formation of a glial scar. Immature astrocytes are able to support robust neurite outgrowth and reduce scarring, therefore, we tested whether these cells would have this effect if transplanted into brain injuries. Utilizing an in vitro spot gradient model that recreates the strongly inhibitory proteoglycan environment of the glial scar we found that, alone, immature, but not mature, astrocytes had a limited ability to form bridges across the most inhibitory outer rim. In turn, the astrocyte bridges could promote adult sensory axon re-growth across the gradient. The use of selective enzyme inhibitors revealed that MMP-2 enables immature astrocytes to cross the proteoglycan rim. The bridge-building process and axon regeneration across the immature glial bridges were greatly enhanced by chondroitinase ABC pretreatment of the spots. We used microlesions in the cingulum of the adult rat brains to test the ability of matrix modification and immature astrocytes to form a bridge for axon regeneration in vivo. Injured axons were visualized via p75 immunolabeling and the extent to which these axons regenerated was quantified. Immature astrocytes coinjected with chondroitinase ABC-induced axonal regeneration beyond the distal edge of the lesion. However, when used alone, neither treatment was capable of promoting axonal regeneration. Our findings indicate that when faced with a minimal lesion, neurons of the basal forebrain can regenerate in the presence of a proper bridge across the lesion and when levels of chondroitin sulfate proteoglycans (CSPGs) in the glial scar are reduced.

Chondroitinase ABC enhances pericontusion axonal sprouting but does not confer robust improvements in behavioral recovery

Traumatic brain injury (TBI) results in enduring functional deficits. Strategies aimed at promoting plasticity within the injured brain may aid in enhancing functional outcome. We have previously shown that spontaneous pericontusional axon sprouting occurs within 7-14 days after controlled cortical impact injury in the adult rat, but ultimately fails due to an increasingly growth-inhibitory environment. We therefore sought to determine whether acute infusion of chondroitinase ABC into the site of the cortical contusion, to further reduce pericontusional growth-inhibitory chondroitin sulfate proteoglycans (CSPGs), would enhance and prolong the sprouting response. We also wanted to determine if chondroitinase-enhanced sprouting would ameliorate the behavioral deficits in forelimb function that occur in this model. Acute chondroitinase infusion decreased intact CSPGs and significantly increased pericontusional cortical grey and white matter growth-associated protein 43 (GAP43)-positive axon sprouting at 7 days post-injury. A return of intact CSPGs at later time points likely contributed to the absence of persistently increased levels of axon sprouting by 14-21 days post-injury. There was no overall benefit on forelimb function during the time of maximal sprouting or at any subsequent times in three of four behavioral outcome measures. However, there was a chondroitinase-induced improvement in recovery from unskilled limb use deficits on the staircase forelimb reaching test toward sham-injured values at 28 days, which was not achieved by the vehicle-treated rats, indicating that there is some minor functional benefit of the increased sprouting induced by chondroitinase treatment. The current results, together with data from spinal cord injury models after chondroitinase intervention, suggest that a combinatorial approach with the addition of neurotrophins and rehabilitation would result in more robust axon sprouting and consequently improve behavioral outcome.

Manipulating the glial scar: chondroitinase ABC as a therapy for spinal cord injury

Chondroitin sulphate proteoglycans (CSPGs) are potent inhibitors of growth in the adult CNS. Use of the enzyme chondroitinase ABC (ChABC) as a strategy to reduce CSPG inhibition in experimental models of spinal cord injury has led to observations of a remarkable capacity for repair. Here we review the evidence that treatment with ChABC, either as an individual therapy or in combination with other strategies, can have multiple beneficial effects on promoting repair following spinal cord injury. These include promoting regeneration of injured axons, plasticity of uninjured pathways and neuroprotection of injured projection neurons. More importantly, ChABC therapy has been demonstrated to promote significant recovery of function to spinal injured animals. Thus, there is robust pre-clinical evidence demonstrating beneficial effects of ChABC treatment following spinal cord injury. Furthermore, these effects have been replicated in a number of different injury models, with independent confirmation by different laboratories, providing an important validation of ChABC as a promising therapeutic strategy. We discuss putative mechanisms underlying ChABC-mediated repair as well as potential issues and considerations in translating ChABC treatment into a clinical therapy for spinal cord injury.

Animals lacking link protein have attenuated perineuronal nets and persistent plasticity

Chondroitin sulphate proteoglycans in the extracellular matrix restrict plasticity in the adult central nervous system and their digestion with chondroitinase reactivates plasticity. However the structures in the extracellular matrix that restrict plasticity are unknown. There are many changes in the extracellular matrix as critical periods for plasticity close, including changes in chondroitin sulphate proteoglycan core protein levels, changes in glycosaminoglycan sulphation and the appearance of dense chondroitin sulphate proteoglycan-containing perineuronal nets around many neurons. We show that formation of perineuronal nets is triggered by neuronal production of cartilage link protein Crtl1 (Hapln1), which is up-regulated in the visual cortex as perineuronal nets form during development and after dark rearing. Mice lacking Crtl1 have attenuated perineuronal nets, but the overall levels of chondroitin sulphate proteoglycans and their pattern of glycan sulphation are unchanged. Crtl1 knockout animals retain juvenile levels of ocular dominance plasticity and their visual acuity remains sensitive to visual deprivation. In the sensory pathway, axons in knockout animals but not controls sprout into the party denervated cuneate nucleus. The organization of chondroitin sulphate proteoglycan into perineuronal nets is therefore the key event in the control of central nervous system plasticity by the extracellular matrix.

Rolipram-induced elevation of cAMP or chondroitinase ABC breakdown of inhibitory proteoglycans in the extracellular matrix promotes peripheral nerve regeneration

The inhibitory growth environment of myelin and extracellular matrix proteoglycans in the central nervous system may be overcome by elevating neuronal cAMP or degrading inhibitory proteoglycans with chondroitinase ABC (ChABC). In this study, we asked whether similar mechanisms operate in peripheral nerve regeneration where effective Wallerian degeneration removes myelin and extracellular proteoglycans slowly. We repaired transected common peroneal (CP) nerve in rats and either elevated cAMP in the axotomized neurons by subcutaneous rolipram, a specific inhibitor of phosphodiesterase IV, and/or promoted degradation of proteoglycans in the distal nerve stump by local ChABC administration. Rolipram treatment significantly increased the number of motoneurons that regenerated axons across the repair site at 1 and 2 weeks, and increased the number of sensory neurons that regenerated axons across the repair site at 2 weeks. Local application of ChABC had a similar effect to rolipram treatment in promoting motor axon regeneration, the effect being no greater when rolipram and ChABC were administered simultaneously. We conclude that blocking inhibitors of axon regeneration by elevating cAMP or degrading proteoglycans in the distal nerve stump promotes peripheral axon regeneration after surgical repair of a transected nerve. It is likely that elevated cAMP is sufficient to encourage axon outgrowth despite the inhibitory growth environment such that simultaneous enzymatic proteoglycan degradation does not promote more axon regeneration than either elevated cAMP or proteoglycan degradation alone.

Traumatic brain injury results in disparate regions of chondroitin sulfate proteoglycan expression that are temporally limited

Axonal injury is a major hallmark of traumatic brain injury (TBI), and it seems likely that therapies directed toward enhancing axon repair could potentially improve functional outcomes. One potential target is chondroitin sulfate proteoglycans (CSPGs), which are major axon growth inhibitory molecules that are generally, but not always, up-regulated after central nervous system injury. The current study was designed to determine temporal changes in cerebral cortical mRNA or protein expression levels of CSPGs and to determine their regional localization and cellular association by using immunohistochemistry in a controlled cortical impact model of TBI. The results showed significant increases in versican mRNA at 4 and 14 days after TBI but no change in neurocan, aggrecan, or phosphacan. Semiquantitative Western blot (WB) analysis of cortical CSPG protein expression revealed a significant ipsilateral decrease of all CSPGs at 1 day after TBI. Lower CSPG protein levels were sustained until at least 14 days, after which the levels began to normalize. Immunohistochemistry data confirm previous reports of regional increases in CSPG proteins after CNS injury, seen primarily within the developing glial scar after TBI, but also corroborate the WB data by revealing wide areas of pericontusional tissue that are deficient in both extracellular and perineuronal net-associated CSPGs. Given the evidence that CSPGs are largely inhibitory to axonal growth, we interpret these data to indicate a potential for regional spontaneous plasticity after TBI. If this were the case, the gradual normalization of CSPG proteins over time postinjury would suggest that this may be temporally as well as regionally limited.

Controlled contusion injury alters molecular systems associated with cognitive performance

We investigated whether a learning impairment after a controlled cortical impact (CCI) injury was associated with alterations in molecules involved in synaptic plasticity and learning and memory. Adult male rats with moderate CCI to the left parietal cortex, tested in a Morris water maze (MWM) beginning at postinjury day 10, showed impaired cognitive performance compared with sham-treated rats. Tissue was extracted for mRNA analysis on postinjury day 21. The expression of brain-derived neurotrophic factor (BDNF), synapsin I, cyclic-AMP response element binding protein (CREB), and calcium-calmodulin-dependent protein kinase II (alpha-CAMKII) were all significantly decreased compared with sham injury levels within the ipsilateral hippocampus after CCI. No significant molecular level changes were found in the contralateral hippocampus. Decreased expression of BDNF and synapsin I was also found within the ipsilateral parietal cortex of CCI-injured rats compared with shams. However, BDNF and synapsin I expressions were significantly increased in the contralateral parietal cortex of the CCI rats. CREB expression was significantly decreased within the contralateral cortex of the CCI group. These findings show enduring reductions in the expression of BDNF, synapsin I, CREB, and alpha-CAMKII ipsilateral to a CCI injury, which seem associated with the spatial learning deficits observed in this injury model. In addition, the delayed increase in the expression of BDNF and synapsin I within the cortex contralateral to CCI may reflect restorative processes in areas homotypical to the injury.

Nutritional tryptophan restriction impairs plasticity of retinotectal axons during the critical period

The use-dependent specification of neural circuits occurs during post-natal development with a conspicuous influence of environmental factors, such as malnutrition that interferes with the major steps of brain maturation. Serotonin (5-HT), derived exclusively from the essential aminoacid tryptophan, is involved in mechanisms of development and use-dependent plasticity of the central nervous system. We studied the effects of the nutritional restriction of tryptophan in the plasticity of uncrossed retinotectal axons following a retinal lesion to the contralateral retina during the critical period in pigmented rats. Litters were fed through their mothers with a low tryptophan content diet, based on corn and gelatin, a complemented diet with standard tryptophan requirements for rodents or standard laboratory diet. The results suggest a marked reduction in the plasticity of intact axons into denervated territories in the tryptophan restricted group in comparison to control groups. Tryptophan complementation between PND10-21 completely restored retinotectal plasticity. However, the re-introduction of tryptophan after the end of the critical period (between PND28-P41) did not restore the sprouting ability of uncrossed axons suggesting a time-dependent effect to the reversion of plasticity deficits. Tryptophan-restricted animals showed a reduced activity of matrix metalloproteinase-9 and altered expressions of phosphorylated forms of ERK1/2 and AKT. Our results demonstrate the influence of this essential aminoacid as a modulator of neural plasticity during the critical period through the reduction of serotonin content which alters plasticity-related signaling pathways and matrix degradation.

Hitting a moving target: Basic mechanisms of recovery from acquired developmental brain injury

Acquired brain injuries represent a major cause of disability in the pediatric population. Understanding responses to developmental acquired brain injuries requires knowledge of the neurobiology of normal development, age-at-injury effects and experience-dependent neuroplasticity. In the developing brain, full recovery cannot be considered as a return to the premorbid baseline, since ongoing maturation means that cerebral functioning in normal individuals will continue to advance. Thus, the recovering immature brain has to 'hit a moving target' to achieve full functional recovery, defined as parity with age-matched uninjured peers. This review will discuss the consequences of developmental injuries such as focal lesions, diffuse hypoxia and traumatic brain injury (TBI). Underlying cellular and physiological mechanisms relevant to age-at-injury effects will be described in considerable detail, including but not limited to alterations in neurotransmission, connectivity/network functioning, the extracellular matrix, response to oxidative stress and changes in cerebral metabolism. Finally, mechanisms of experience-dependent plasticity will be reviewed in conjunction with their effects on neural repair and recovery.

Synaptophysin expression in rat retina following acute high intraocular pressure

In response to injury, synapse alteration may occur earlier than the changes in the cell body of neurons. Although retinal ganglion cell death and thinning of the inner part of retina were found after acute high intraocular pressure (HIOP), the structural and functional changes of synapses in the retina remain unknown. In the present study, we investigated the protein and mRNA expression of synaptophysin (SYN), an important molecule closely related to synaptic activities, synaptogenesis and synaptic plasticity. In addition, we also studied the ultrastructural changes of the retinal synapses. We found that (1) synaptophysin was upregulated transiently at both protein and mRNA level following HIOP; (2) broadened distribution of synaptophysin protein was present within the outer nuclear layer at the early stage following HIOP; (3) in the outer nuclear layer bouton-like vesicle-containing structures were observed by electron microscopy. This data suggested that, besides degeneration, synapses in rat retina may undergo regenerative events following HIOP.

Neuroregenerative strategies in the brain: emerging significance of bone morphogenetic protein 7 (BMP7)

Every year thousands of people suffer from brain injuries and stroke, and develop motor, sensory, and cognitive problems as a result of neuronal loss in the brain. Unfortunately, the damaged brain has a limited ability to enact repair and current modes of treatment are not sufficient to offset the damage. An extensive list of growth factors, neurotrophic factors, cytokines, and drugs has been explored as potential therapies. However, only a limited number of them may actually have the potential to effectively offset the brain injury or stroke-related problems. One of the treatments considered for future brain repair is bone morphogenetic protein 7 (BMP7), a factor currently used in patients to treat non-neurological diseases. The clinical application of BMP7 is based on its neuroprotective role in stroke animal models. This paper reviews the current approaches considered for brain repair and discusses the novel convergent strategies by which BMP7 potentially can induce neuroregeneration.

Benefit of chondroitinase ABC on sensory axon regeneration in a laceration model of spinal cord injury in the rat

BACKGROUND

Chondroitin sulfate proteoglycans are up-regulated in the spinal cord after SCI, creating a molecular barrier inhibitory to axon growth. Chondroitinase ABC degrades CSPGs in vitro and in vivo.

METHODS

We studied whether IT ChABC promotes axonal regeneration in a laceration model of SCI. Three groups of Sprague-Dawley rats were used: control and rats treated with low-dose and high-dose IT ChABC. Chondroitin sulfate proteoglycan breakdown products were measured by 2-B-6 expression, and intact CSPGs by CS-56 expression. Sensory axonal regeneration was traced after CTB injection into the median, ulnar, and sciatic nerves.

RESULTS

CS-56 expression was down-regulated and 2-B-6 expression was increased in the groups treated with IT ChABC but not in the control. Laminin and GFAP immunoreactivity was unaltered in the ChABC groups. The number of axons growing into the scar was 3.1 times greater (P < .01) in the high-dose ChABC group and 2.1 times greater (P < .01) in the low-dose group compared with the controls. The length of axonal growth after high- and low-dose ChABC was 9.9 (P < .01) and 8.3 (P < .01) times greater, respectively, than in the control group. Axons extended across the lesion gap and into the distal spinal cord stump in 2 of 8 (low dose) and in 3 of 9 (high dose) rats compared with none in the control group.

CONCLUSIONS

Intrathecal ChABC administration caused a slight decrease in CSPGs in the scar after a laceration SCI with a minimal increase in sensory axonal regeneration into and across the laceration gap.

Distribution and synthesis of extracellular matrix proteoglycans, hyaluronan, link proteins and tenascin-R in the rat spinal cord

Perineuronal nets (PNNs) are dense extracellular matrix (ECM) structures that form around many neuronal cell bodies and dendrites late in development. They contain several chondroitin sulphate proteoglycans (CSPGs), hyaluronan, link proteins and tenascin-R. Their time of appearance correlates with the ending of the critical period for plasticity, and they have been implicated in this process. The distribution of PNNs in the spinal cord was examined using Wisteria floribunda agglutinin lectin and staining for chondroitin sulphate stubs after chondroitinase digestion. Double labelling with the neuronal marker, NeuN, showed that PNNs were present surrounding approximately 30% of motoneurons in the ventral horn, 50% of large interneurons in the intermediate grey and 20% of neurons in the dorsal horn. These PNNs formed in the second week of postnatal development. Immunohistochemical staining demonstrated that the PNNs contain a mixture of CSPGs, hyaluronan, link proteins and tenascin-R. Of the CSPGs, aggrecan was present in all PNNs while neurocan, versican and phosphacan/RPTPbeta were present in some but not all PNNs. In situ hybridization showed that aggrecan and cartilage link protein (CRTL 1) and brain link protein-2 (BRAL 2) are produced by neurons. PNN-bearing neurons express hyaluronan synthase, and this enzyme and phosphacan/RPTPbeta may attach PNNs to the cell surface. During postnatal development the expression of link protein and aggrecan mRNA is up-regulated at the time of PNN formation, and these molecules may therefore trigger their formation.