Temporal and spatial distribution of growth-associated molecules and astroglial cells in the rat corticospinal tract during development

Inhibition of CSPG-PTPσ Activates Autophagy Flux and Lysosome Fusion, Aids Axon and Synaptic Reorganization in Spinal Cord Injury

Chondroitin sulfate proteoglycans (CSPGs) and proteoglycan receptor protein tyrosine phosphatase σ (PTPσ) play a critical role in the pathology of spinal cord injury (SCI). CSPGs can be induced by autophagy inhibition in astrocyte. However, CSPG's impact on autophagy and its role in SCI is still unknown. We investigate intracellular sigma peptide (ISP) targeting PTPσ, its effects on autophagy, and synaptic reorganization in SCI. We found that ISP increased the level of autophagosome marker LC3B-II/I and decreased autophagosome degradation marker p62 in SCI, suggesting activated autophagy flux. ISP restored autophagosome-lysosome fusion-related protein syntaxin 17 (STX17) and lysosome-associated membrane protein 2 (LAMP2), indicating activated autophagosome-lysosome fusion. ISP increased pre-synaptic marker synaptophysin (SYN) and postsynaptic density protein-95 (PSD-95) expression and improved excitatory synapse marker vesicular glutamate transporter 1 (VGLUT1) and SYN in SCI, suggesting improved synaptic reorganization. ISP promoted axon marker neurofilament and growth-related GAP-43 expression in SCI. ISP rescued a preserved number of motor neurons and improved neurobehavioral recovery after SCI. Our study extended the CSPG-PTPσ inhibition role in activating autophagy flux, axon and synaptic reorganization, and functional recovery in SCI.

Effect and Mechanism of Yisui Fuyongtang (YSFYT) Decoction on Cognitive Function and Synaptic Plasticity in Rats with Vascular Cognitive Impairment

Vascular cognitive impairment (VCI) has emerged as the second major disease responsible for dementia, and there is still a lack of effective treatment methods for this disorder to date. Clinical medications have found that Yisui Fuyongtang (YSFYT) Decoction is effective in improving neurological signs and learning-memory functions in patients who develop white matter lesions and whole brain atrophy. To clarify the effect and molecular regulation mechanism of YSFYT Decoction on model rats, this research analyzed the influence of YSFYT Decoction on the learning-memory ability and lipid metabolism of rats based on behavioral and biochemical analysis. Further pathology and protein detection methods were adopted to investigate the action of YSFYT Decoction on the neurons in the hippocampus of model rats and the regulation of the brain derived neurotrophic factor (BDNF)-tyrosine protein kinase receptor B (TrkB) signaling pathway. Compared with the VCI group, after YSFYT Decoction administration, the ratio of swimming time in the platform, number of crossing the platform, number of active avoidance, and proportion of active avoidance of the rats were markedly increased, whereas the response latency was substantially reduced (p < 0.05). Biochemical tests indicated that contents of lipoprotein lipase (LPL), triglyceride (TG), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), and high-density lipoprotein cholesterol (HDL-C) of the model rats in YSFYT Decoction treatment group were greatly reduced, whereas those of total antioxidant capacity (T-AOC), glutathione peroxidase (GSH-PX), catalase (CAT), malondialdehyde (MDA), and superoxide dismutase (SOD) were elevated (p < 0.05). Additionally, Bcl-2 expression in YSFYT Decoction treatment group was significantly increased, but neuron apoptosis of the hippocampus tissue was reduced. Meanwhile, neuron number was apparently higher than that in VCI model group. Following Yisui Decoction treatment, expressions of growth-associated protein 43 (GAP43), synaptophysin (SYP), postsynaptic density 95 (PSD95), NMDAR subunit 2B (NR2B), BDNF, TrkB, phospho-mitogen-activated protein kinase (p-MAPK), extracellular signal-regulated kinase (ERK), phosphatidylinositol 3-kinase (PI3K), and phospho-protein kinase B (p-AKT) were markedly elevated. Taken together, YSFYT Decoction could activate the BDNF-TrkB signaling pathway, elevate Bcl-2 expression, and minimize neuronal apoptosis in hippocampus, thereby improving the behavioral characteristics and biochemical indicators of the VCI rat model.

NEP1‑40 promotes myelin regeneration via upregulation of GAP‑43 and MAP‑2 expression after focal cerebral ischemia in rats

Axon regeneration after lesions to the central nervous system (CNS) is largely limited by the presence of growth inhibitory molecules expressed in myelin. Nogo‑A is a principal inhibitor of neurite outgrowth, and blocking the activity of Nogo‑A can induce axonal sprouting and functional recovery. However, there are limited data on the expression of Nogo‑A after CNS lesions, and the mechanism underlying its influences on myelin growth remains unknown. The aim of the present study was to observe the time course of Nogo‑A after cerebral ischemia/reperfusion in rats using immunohistochemistry and western blot techniques, and to test the effect of its inhibitor Nogo extracellular peptide 1‑40 (NEP1‑40) on neural plasticity proteins, growth‑associated binding protein 43 (GAP‑43) and microtubule associated protein 2 (MAP‑2), as a possible mechanism underlying myelin suppression. A classic model of middle cerebral artery occlusion (MCAO) was established in Sprague‑Dawley rats, which were divided into three groups: i) MCAO model group; ii) MCAO + saline group; and iii) MCAO + NEP1‑40 group. Rats of each group were divided into five subgroups by time points as follows: days 1, 3, 7, 14 and 28. Animals that only received sham operation were used as controls. The Nogo‑A immunoreactivity was located primarily in the cytoplasm of oligodendrocytes. The number of Nogo‑A immunoreactive cells significantly increased from day 1 to day 3 after MCAO, nearly returning to the control level at day 7, increased again at day 14 and decreased at day 28. Myelin basic protein (MBP) immunoreactivity in the ipsilateral striatum gradually decreased from day 1 to day 28 after ischemia, indicating myelin loss appeared at early time points and continuously advanced during ischemia. Then, intracerebroventricular infusion of NEP1‑40, which is a Nogo‑66 receptor antagonist peptide, was administered at days 1, 3 and 14 after MCAO. It was observed that GAP‑43 considerably increased from day 1 to day 7 and then decreased to a baseline level at day 28 compared with the control. MAP‑2 expression across days 1‑28 significantly decreased after MCAO. Administration of NEP1‑40 attenuated the reduction of MBP, and upregulated GAP‑43 and MAP‑2 expression at the corresponding time points after MCAO compared with the MCAO + saline group. The present results indicated that NEP1‑40 ameliorated myelin damage and promoted regeneration by upregulating the expression of GAP‑43 and MAP‑2 related to neuronal and axonal plasticity, which may aid with the identification of a novel molecular mechanism of restriction in CNS regeneration mediated by Nogo‑A after ischemia in rats.

The Role of Chondroitin Sulfate Proteoglycans in Nervous System Development

The orderly development of the nervous system is characterized by phases of cell proliferation and differentiation, neural migration, axonal outgrowth and synapse formation, and stabilization. Each of these processes is a result of the modulation of genetic programs by extracellular cues. In particular, chondroitin sulfate proteoglycans (CSPGs) have been found to be involved in almost every aspect of this well-orchestrated yet delicate process. The evidence of their involvement is complex, often contradictory, and lacking in mechanistic clarity; however, it remains obvious that CSPGs are key cogs in building a functional brain. This review focuses on current knowledge of the role of CSPGs in each of the major stages of neural development with emphasis on areas requiring further investigation.

Animal models of developmental motor disorders: parallels to human motor dysfunction in cerebral palsy

Cerebral palsy (CP) is the most common motor disability in children. Much of the previous research on CP has focused on reducing the severity of brain injuries, whereas very few researchers have investigated the cause and amelioration of motor symptoms. This research focus has had an impact on the choice of animal models. Many of the commonly used animal models do not display a prominent CP-like motor phenotype. In general, rodent models show anatomically severe injuries in the central nervous system (CNS) in response to insults associated with CP, including hypoxia, ischemia, and neuroinflammation. Unfortunately, most rodent models do not display a prominent motor phenotype that includes the hallmarks of spasticity (muscle stiffness and hyperreflexia) and weakness. To study motor dysfunction related to developmental injuries, a larger animal model is needed, such as rabbit, pig, or nonhuman primate. In this work, we describe and compare various animal models of CP and their potential for translation to the human condition.

Changes and Significance of SYP and GAP-43 Expression in the Hippocampus of CIH Rats

Synaptophysin (SYP) and growth-associated binding protein 43 (GAP-43) have been shown to be closely related to hippocampal synaptic plasticity in recent years. They are important molecular markers associated with synaptic plasticity. However, the role of SYP and GAP-43 in chronic intermittent hypoxic injury of the central nervous system needs to be further clarified. In this study, 25 adult male sprague dawley (SD) rats were randomly divided into a normal control group (CON) and a chronic intermittent hypoxia group (CIH) with four time points as follows: 1 W, 2 W, 3 W, and 4 W. The behavioural changes (primarily learning and memory abilities) were observed by the Morris water maze in each group, consisting of 5 rats per group.The localization of SYP and GAP-43 in hippocampal CA1 neurons was observed, and the expression of SYP and GAP-43 in the hippocampus was detected by Western blotting. The results showed that the mean oxygen saturation of the tail artery in CIH rats was less than that in normal rats (P < 0.05). The escape latency of CIH rats was longer than that of normal rats, and the number of space exploration platform crossings was less than that of normal rats. SYP-positive stained cells were yellow or brown and were mainly expressed on the cell membrane, while the GAP-43-positive staining was brown and was mainly expressed on the cell membrane and in the cytoplasm. The expression of SYP in plasma decreased gradually at the four time points for the CIH group (P < 0.05), while the expression of GAP-43 in the CIH 1W group increased (P < 0.05) and decreased gradually in the CIH 2 W, CIH 3 W and CIH 4 W groups (P < 0.05).

Influence of chronic intermittent hypoxia on growth associated protein 43 expression in the hippocampus of young rats

This study aimed to explore the pathological change to hippocampal neurons and the expression of growth associated protein 43 in 21-day-old young rats following chronic intermittent hypoxia. Hematoxylin-eosin staining results showed varying degrees of degeneration and necrosis in hippocampal neurons depending on the modeling time. Immunohistochemistry revealed that growth associated protein 43 expression in young rats following chronic intermittent hypoxia decreased, but that levels were still higher than those of normal rats at each time point, especially 4 weeks after modeling. During 1–5 weeks after modeling, a slow growth in rat weight was observed. Experimental findings indicate that chronic intermittent hypoxia may induce growth dysfunction and necrosis of hippocampal neurons, as well as increase the expression of growth associated protein 43 in young rats.

Do sensorimotor β-oscillations maintain muscle synergy representations in primary motor cortex?

Coherent β-oscillations are a dominant feature of the sensorimotor system yet their function remains enigmatic. We propose that, in addition to cell intrinsic and/or local network interactions, they are supported by activity propagating recurrently around closed neural 'loops' between primary motor cortex (M1), muscles, and back to M1 via somatosensory pathways. Individual loops reciprocally connect individual muscle synergies ('motor primitives') with their representations in M1, and the conduction time around each loop resonates with the periodic spiking of its constituent neurons/muscles. During β-oscillations, this resonance strengthens within-loop connectivity (via long-term potentiation, LTP), whereas non-resonance between different loops weakens connectivity (via long-term depression, LTD) between M1 representations of different muscle synergies. In this way, β-oscillations help maintain accurate and discrete representations of muscle synergies in M1.

Biodegradable biomatrices and bridging the injured spinal cord: the corticospinal tract as a proof of principle

Important advances in the development of smart biodegradable implants for axonal regeneration after spinal cord injury have recently been reported. These advances are evaluated in this review with special emphasis on the regeneration of the corticospinal tract. The corticospinal tract is often considered the ultimate challenge in demonstrating whether a repair strategy has been successful in the regeneration of the injured mammalian spinal cord. The extensive know-how of factors and cells involved in the development of the corticospinal tract, and the advances made in material science and tissue engineering technology, have provided the foundations for the optimization of the biomatrices needed for repair. Based on the findings summarized in this review, the future development of smart biodegradable bridges for CST regrowth and regeneration in the injured spinal cord is discussed.

The challenges of long-distance axon regeneration in the injured CNS

Injury to the central nervous system (CNS) that results in long-tract axonal damage typically leads to permanent functional deficits in areas innervated at, and below, the level of the lesion. The initial ischemia, inflammation, and neurodegeneration are followed by a progressive generation of scar tissue, dieback of transected axons, and demyelination, creating an area inhibitory to regrowth and recovery. Two ways to combat this inhibition is to therapeutically target the extrinsic and intrinsic properties of the axon-scar environment. Scar tissue within and surrounding the lesion site can be broken down using an enzyme known as chondroitinase. Negative regulators of adult neuronal growth, such as Nogo, can be neutralized with antibodies. Both therapies greatly improve functional recovery in animal models. Alternatively, modifying the intrinsic growth properties of CNS neurons through gene therapy or pharmacotherapy has also shown promising axonal regeneration after injury. Despite these promising therapies, the main challenge of long-distance axon regeneration still remains; achieving a level of functional and organized connectivity below the level of the lesion that mimics the intact CNS.

Laser-guided cell micropatterning system

Employing optical force, our laser-guided cell micropatterning system, is capable of patterning different cell types onto and within standard cell research devices, including commercially available multielectrode arrays (MEAs) with glass culture rings, 35 mm Petri dishes, and microdevices microfabricated with polydimethylsiloxane on 22 mm × 22 mm cover glasses. We discuss the theory of optical forces for generating laser guidance and the calculation of optimal beam characteristics for cell guidance. We describe the hardware design and software program for the cell patterning system. Finally, we demonstrate the capabilities of the system by (1) patterning neurons to form an arbitrary pattern, (2) patterning neurons onto the electrodes of a standard MEA, and (3) patterning and aligning adult cardiomyocytes in a polystyrene Petri dish.

Pericontusion axon sprouting is spatially and temporally consistent with a growth-permissive environment after traumatic brain injury

We previously reported that pericontusional extracellular chondroitin sulfate proteoglycans (CSPGs) are profoundly reduced for 3 weeks after experimental traumatic brain injury, indicating a potential growth-permissive window for plasticity. Here, we investigate the extracellular environment of sprouting neurons after controlled cortical impact injury in adult rats to determine the spatial and temporal arrangement of inhibitory and growth-promoting molecules in relation to growth-associated protein 43-positive (GAP43+) neurons. Spontaneous cortical sprouting was maximal in pericontused regions at 7 and 14 days after injury but absent by 28 days. Perineuronal nets containing CSPGs were reduced at 7 days after injury in the pericontused region (p < 0.05), which was commensurate with a reduction in extracellular CSPGs. Sprouting was restricted to the perineuronal nets and CSPG-deficient regions at 7 days, indicating that the pericontused region is temporarily and spatially permissive to new growth. At this time point,GAP43+ neurons were associated with brain regions containing cells positive for polysialic acid neural cell adhesion molecule but not with fibronectin-positive cells. Brain-derived neurotrophic factor was reduced in the immediate pericontused region at 7 days. Along with prior Western blot evidence, these data suggest that a lowered intrinsic growth stimulus, together with a later return of growth-inhibitory CSPGs, may contribute to the ultimate disappearance of sprouting neurons after traumatic brain injury.

Rho kinase inhibitor Fasudil induces neuroprotection and neurogenesis partially through astrocyte-derived G-CSF

Rho-kinases (ROCK) are serine/threonine kinases that play an important role in fundamental processes of cell migration, proliferation and survival. Blockade of ROCK promotes axonal regeneration and neuroprotection, thereby exhibiting therapeutic potentials for clinical application to spinal cord damage and stroke. Here we explored the mechanisms of Fasudil, a ROCK inhibitor, in neuroprotection and neurogenesis by using oxygen-glucose deprivation (OGD) as an in vitro ischemia model. Fasudil stimulates astrocytes to produce granulocyte colony-stimulating factor (G-CSF). Astrocyte-conditioned medium treated with Fasudil (ACM-F) contributes to the generation of neurospheres, and decreases neuron death. Neutralization of G-CSF in ACM-F and blocking of G-CSF receptor in neuronal cell cultures revealed that Fasudil-induced neuroprotection and/or neurogenesis are mediated partially through astrocyte-derived G-CSF. Our results indicate that ROCK inhibition by Fasudil, protecting neurons and mobilizating neural stem cells, might represent a useful therapeutic perspective for various neurological disorders characterized by neuron death.

Abnormal growth of the corticospinal axons into the lumbar spinal cord of the hyt/hyt mouse with congenital hypothyroidism

Thyroid hormone deficiency may cause severe neurological disorders resulting from developmental deficits of the central nervous system. The mutant hyt/hyt mouse, characterized by fetal-onset, life-long hypothyroidism resulting from a point mutation of the thyroid-stimulating hormone receptor of the thyroid gland, displays a variety of abnormalities in motor behavior that are likely associated with dysfunctions of specific brain regions and a defective corticospinal tract (CST). To test the hypothesis that fetal and neonatal hypothyroidism cause abnormal CST development, the growth of the CST was investigated in hypothyroid hyt/hyt mice and their euthyroid progenitors, the BALB/cByJ mice. Anterograde labeling with biotinylated dextran amine demonstrated a decrease in the number of CST axons in the hyt/hyt mouse at the first lumbar level at postnatal day (P) 10. After retrograde tracing with fast blue (FB), fewer FB-labeled neurons were found in the motor cortex, the red nucleus, and the lateral vestibular nucleus of the hyt/hyt mouse. At the fourth lumbar level, the hyt/hyt mouse also showed smaller CST cross-sectional areas and significantly lower numbers of unmyelinated axons, myelinated axons, and growth cones within the CST during postnatal development. At P10, the hyt/hyt mouse demonstrated significantly lower immunoreactivity of embryonic neural cell adhesion molecule in the CST at the seventh cervical level, whereas the expression of growth-associated protein 43 remained unchanged. Our study demonstrated an abnormal development of the CST in the hyt/hyt mouse, manifested by reduced axon quantity and retarded growth pattern at the lumbar spinal cord.

ROCK inhibition with Y27632 activates astrocytes and increases their expression of neurite growth-inhibitory chondroitin sulfate proteoglycans

Inhibition of Rho-kinase (ROCK) with Y27632 stimulates sprouting by injured corticospinal tract and dorsal column tract axons, and accelerates functional recovery. However, regeneration of these axons across the glial scar was not observed. Here we examined the effects of Y27632 treatment on chondroitin sulfate proteoglycan (CSPG) expression by astrocytes, which are a key component of the reactive gliosis inhibiting axonal regeneration. In vivo, rats underwent a dorsal column transection and were treated with Y27632 via intrathecal pump infusion. Compared with controls, Y27632-treated injury sites displayed exaggerated upregulation of glial fibrillary acid protein and neurocan immunoreactivity along the lesion edge. In vitro, astrocytes assumed a reactive morphology (stellate shape) and increased their expression of CSPGs after Y27632 treatment. Neurite growth by dissociated cortical neurons decreased when cultured on the extracellular matrix (ECM) derived from Y27632-treated astrocytes. This decrease in neurite growth was reversed with chondroitinase-ABC (ChABC) digestion, indicating that the inhibition was due to CSPG depositions within the ECM. Interestingly, conditioned medium (CM) from untreated astrocytes was inhibitory to neurite growth, which was overcome by ChABC digestion. Such inhibitory activity was not found in the CM of Y27632-treated astrocytes. Taken together, these data support a model where ROCK inhibition by Y27632 modifies astrocytic processing of CSPGs, and increases the presence of CSPGs within the ECM while reduces CSPGs in the CM (cerebrospinal fluid in vivo). This increased expression of inhibitory CSPGs in the ECM of the glial scar may counteract the growth promoting effects of ROCK inhibition on axonal growth cones.

Matrix metalloproteinase-2 facilitates wound healing events that promote functional recovery after spinal cord injury

Matrix metalloproteinases (MMPs) are proteolytic enzymes that are involved in both injury and repair mechanisms in the CNS. Pharmacological blockade of MMPs, limited to the first several days after spinal cord injury, improves locomotor recovery. This beneficial response is, however, lost when treatment is extended beyond the acutely injured cord to include wound healing and tissue remodeling. This suggests that some MMPs play a beneficial role in wound healing. To test this hypothesis, we investigated the role of MMP-2, which is actively expressed during wound healing, in white matter sparing and axonal plasticity, the formation of a glial scar, and locomotor recovery after spinal cord injury. MMP-2 increased between 7 and 14 d after injury, where it was immunolocalized in reactive astrocytes bordering the lesion epicenter. There was reduced white matter sparing and fewer serotonergic fibers, caudal to the lesion in injured MMP-2 null animals. MMP-2 deficiency also resulted in increased immunoreactivity to chondroitin sulfate proteoglycans and a more extensive astrocytic scar. Most importantly, locomotion in an open field, performance on a rotarod, and grid walking were significantly impaired in injured MMP-2 null mice. Our findings suggest that MMP-2 promotes functional recovery after injury by regulating the formation of a glial scar and white matter sparing and/or axonal plasticity. Thus, strategies exploiting MMPs as therapeutic targets must balance these beneficial effects during wound healing with their adverse interactions in the acutely injured spinal cord.

Degradation of chondroitin sulfate proteoglycans potentiates transplant-mediated axonal remodeling and functional recovery after spinal cord injury in adult rats

Transplantation of growth-permissive cells or tissues was used to bridge a lesion cavity and induce axonal growth in experimental spinal cord injury (SCI). Axonal interactions between host and transplant may be affected by upregulation of inhibitory chondroitin sulfate proteoglycans (CSPGs) following various transplantation strategies. The extent of axonal growth and functional recovery after transplantation of embryonic spinal cord tissue decreases in adult compared to neonatal host. We hypothesized that CSPGs contribute to the decrease in the extent to which transplant supports axonal remodeling and functional recovery. Expression of CSPGs increased after overhemisection SCI in adult rats but not in neonates. Embryonic spinal cord transplant was surrounded by CSPGs deposited in host cord, and the interface between host and transplant seemed to contain a large amount of CSPGs. Intrathecally delivered chondroitinase ABC (C'ase) improved recovery of distal forelimb usage and skilled motor behavior after C4 overhemisection injury and transplantation in adults. This behavioral recovery was accompanied by an increased amount of raphespinal axons growing into the transplant, and raphespinal innervation to the cervical motor region was promoted by C'ase plus transplant. Moreover, C'ase increased the number of transplanted neurons that grew axons to the host cervical enlargement, suggesting that degradation of CSPGs supports remodeling not only of host axons but also axons from transplanted neurons. Our results suggest that CSPGs constitute an inhibitory barrier to prevent axonal interactions between host and transplant in adults, and degradation of the inhibitory barrier can potentiate transplant-mediated axonal remodeling and functional recovery after SCI.

Regeneration following spinal cord injury, from experimental models to humans: where are we?

Regeneration in the adult CNS following injury is extremely limited. Traumatic spinal cord injury causes a permanent neurological deficit followed by a very limited recovery due to failed regeneration attempts. In fact, it is now clear that the spinal cord intrinsically has the potential to regenerate, but cellular loss and the presence of an inhibitory environment strongly limit tissue regeneration and functional recovery. The molecular mechanisms responsible for failed regeneration are starting to be unveiled. This gain in knowledge led to the design of therapeutic strategies aimed to limit the tissue scar, to enhance the proregeneration versus the inhibitory environment, and to replace tissue loss, including the use of stem cells. They have been very successful in several animal models, although results are still controversial in humans. Nonetheless, novel experimental approaches hold great promise for use in humans.

Development of the corticospinal tract in the mouse spinal cord: A quantitative ultrastructural analysis

The growth of corticospinal tract (CST) axons was studied quantitatively at the 7th cervical (C7) and the 4th lumbar (L4) spinal segments in the balb/cByJ mice at the ages of postnatal day (P) 0, 2, 4, 6, 8, 10, 14, and 28. The cross-sectional area of the CST increased progressively with time. Unmyelinated axons, the most prominent CST element during early development, reached maximum at C7 and L4 on P14. Two phases of increase in the number of unmyelinated axons were observed at C7, while only one surge of axonal outgrowth was found at the L4 level. Pro-myelinated axons, defined as axons surrounded by only one layer of oligodendrocytic process, were first seen at P2 and P4 in the C7 and the L4 level, respectively, followed by a dramatic increase in the number of myelinated axons from P14 onwards at both spinal levels. Myelination of the CST axons occurred topographically in a dorsal-to-ventral pattern. The number of growth cones increased rapidly at the C7 level to reach its maximum at P4, while those at L4 increased steadily to the peak at P10. Growth cones with synapse-like junctions were occasionally observed in the growing CST. Degenerating axons and growth cones partly accounted for the massive axon loss at both spinal segments during CST development. Overall, the mouse CST elements changed dynamically in numbers during postnatal development, suggesting a vigorous growing and pruning activity in the tract. The mouse CST also showed a similar growth pattern to that of the rat CST.

Early profiles of axonal growth and astroglial response after spinal cord hemisection and implantation of Schwann cell-seeded guidance channels in adult rats

We previously demonstrated that transplantation of Schwann cell-seeded channels promoted the regrowth of injured axons in the adult spinal cord. It is not clear, however, whether injured axons recapitulate the developmental scenarios to accomplish regeneration. In the present study, we investigated the early events associated with axonal regrowth after spinal cord hemisection at the eighth thoracic level and implantation of a Schwann cell-seeded minichannel in adult rats. Animals were sacrificed at postoperative days (PO) 2, 4, 7, and 14. Anterograde tracing with fluoro-ruby showed that regenerating axons grew into the graft prior to PO2 and reached the distal end of the channel at PO7. These axons expressed both embryonic neural cell adhesion molecule (E-NCAM) and growth associated protein-43 (GAP-43). Although the expression of E-NCAM decreased by PO7, that of GAP-43 remained high throughout the first 2 weeks after implantation. A close relation of vimentin-positive astroglia to the growing axons in the host tissue suggested a contact-mediated role of these cells in axon guidance. Aggregation of glial fibrillary acidic protein (GFAP)-positive astrocytes together with the increased expression of chondroitin sulfate proteoglycans (CSPGs) starting at PO7 appeared to inhibit axonal growth at the host-graft interface. Thus, adult regenerating axons and astroglia do express developmentally related molecules that may facilitate axonal growth into a permissive graft at the early phase of injury and regeneration. These results suggest that molecules and astroglia essential to development are both important in influencing axonal regrowth in the adult spinal cord.