Regenerating corticospinal fibers in the Marmoset (Callitrix jacchus) after spinal cord lesion and treatment with the anti-Nogo-A antibody IN-1

Neutralizing the myelin-associated growth inhibitor Nogo-A in adult spinal cord-injured rats can promote regeneration of injured and compensatory sprouting of uninjured axons. Nogo-A is present in humans, making its neutralization a possible novel treatment option for paraplegic patients. In this study we examined the effects of an extensively used anti-Nogo-A antibody (mAb IN-1) on the regenerative capabilities of lesioned corticospinal tract (CST) axons in a primate, the Marmoset monkey. Unilateral thoracic lesions of the CST were performed in six adult Marmosets, followed by the application of mAb IN-1 into the cerebrospinal fluid circulation by a graft of hybridoma cells. A unilateral injection of biotin dextran amine into the motor cortex was performed to analyse sprouting and regeneration of the lesioned axons. In the control antibody-treated animal CST fibers stopped rostral to the lesion site and often showed retraction bulbs. In contrast, in four out of five mAb IN-1-treated animals fine labeled neurites had grown into, through and around the lesion site. Thus, this study provides first anatomical evidence that in primates, the neutralization of the myelin-associated inhibitor Nogo-A results in increased regenerative sprouting and growth of lesioned spinal cord axons.     

Sprouting and Regeneration of Lesioned Corticospinal Tract Fibres in the Adult Rat Spinal Cord

We have studied the effects of tissue transplants and antibodies (IN-1) against the myelin-associated neurite growth inhibitory proteins on sprouting and regeneration of the rat corticospinal tract (CST). Transplantation of embryonic spinal cord tissue into bilateral transection lesions of the lower thoracic spinal cord in young adult rats resulted in a marked increase of the sprouting of the lesioned CST. This sprouting effect was probably elicited by soluble factors released from the transplants, and was enhanced by the IN-1 antibodies. The retraction of lesioned CST fibres normally observed with prolonged survival times was also reduced by the presence of transplants. In spite of these growth-promoting effects of the transplants, the regenerative elongation of CST sprouts into the caudal spinal cord was dependent upon the neutralization of the myelin-associated inhibitory proteins. In the controls (no antibodies or control antibodies) only 27% of the animals showed elongation of CST fibres exceeding the sprouting distance of 0.7 mm. These fibres grew to a maximal length of 1.8 mm (mean±SEM, 1.2±0.1). In contrast, 60% of the IN-1-treated, transplant-containing rats showed elongations of >0.7 mm, and these fibres grew up to 10.1 mm (4.6±0.5). Regenerating fibres crossed the lesion site through remaining tissue bridges. Neither embryonic spinal cord transplants nor a variety of implanted bridge materials could serve as a substrate for the regenerating CST axons.     

Regeneration and Sprouting of Chronically Injured Corticospinal Tract Fibers in Adult Rats Promoted by NT-3 and the mAb IN-1, Which Neutralizes Myelin-Associated Neurite Growth Inhibitors

Myelin-associated inhibitors of neurite growth play an important role in the regenerative failure after injury in the adult mammalian CNS. The application of the mAb IN-1, which efficiently neutralizes the NI-250/35 inhibitory proteins, alone or in combination with neurotrophin-3 (NT-3), has been shown to promote axonal regeneration when applied in acute injury models. To test whether IN-1 application can induce axonal growth also in a chronic injury model, we treated rats with IN-1 and NT-3 starting 2 or 8 weeks after injury. Rats underwent bilateral dorsal hemisection of the spinal cord at the age of 5–6 weeks. Regeneration of corticospinal (CST) fibers into the caudal spinal cord was observed in three of eight of those animals with a 2-week delay between lesion and treatment. CST fibers regenerated for 2–11.4 mm. In the control group sprouting occurred rostral to the lesion but no long-distance regeneration occurred. In animals where treatment started at 8 weeks after injury the longest fibers observed grew up to 2 mm into the caudal spinal cord. The results show that transected corticospinal axons retain the ability to regenerate at least for a few weeks after injury. Functional analysis of these animals showed a slight improvement of functional recovery.     

Improving axonal growth and functional recovery after experimental spinal cord injury by neutralizing myelin associated inhibitors

Injuries of the spinal cord often result in an irretrievable loss of motor and sensory functions of all body parts situated below the lesion site. Functional recovery is restricted mainly due to the limited regeneration and plasticity of injured axons in the adult central nervous system. Over the last few years different experimental approaches have led to axonal growth and functional benefits in animal models. This review focuses on the effects of the neutralization of myelin-associated neurite growth inhibitors, in particular Nogo-A, using the monoclonal antibody IN-1. Acute mAb IN-1 treatment of adult CNS lesioned rats results in extensive plastic changes of neuronal connections and regenerative fiber growth. In two different lesion paradigms (i.e. pyramidal tract lesion and incomplete spinal cord lesion in adult rats), the mAb IN-1-treated animals always showed a higher degree of recovery in various behavioral tests. These observations, together with electrophysiological results, suggest that neuronal CNS circuits of mAb IN-1-treated animals can be rearranged, and that sprouting and regenerating axons form functionally meaningful connections.     

Behavioral recovery and anatomical plasticity in adult rats after cortical lesion and treatment with monoclonal antibody IN-1

We have previously reported that monoclonal antibody (mAb) IN-1 treatment after ischemic infarct in adult rats results in significant recovery of skilled forelimb use. Such recovery was correlated with axonal outgrowth from the intact, opposite motor cortex into deafferented subcortical motor areas. In the present study, we investigated the effects of mAb IN-1 treatment after adult sensorimotor cortex (SMC) aspiration lesion on behavioral recovery and neuroanatomical plasticity in the corticospinal tract. Adult rats underwent unilateral SMC aspiration lesion and treatment with either mAb IN-1 or a control Ab, or no treatment. Animals were then tested over a 6-week period in the skilled forelimb use task and the skilled ladder rung walking task. We found that animals treated with mAb IN-1 after SMC lesion fully recovered the use of forelimb reaching, but showed no improvement in digit grasping as tested in the skilled forelimb use task. The mAb IN-1 treatment group was also significantly improved as compared to control groups in the skilled ladder rung walking test. Furthermore, neuroanatomical tracing revealed a significant increase in the corticospinal projections into the deafferented motor areas of the spinal cord after mAb IN-1 treatment. These results indicate that treatment with mAb IN-1 after cortical aspiration lesion induces remodeling of motor pathways resulting in recovery in only certain behavioral tasks, suggesting that the cause of brain damage influences behavioral recovery after mAb IN-1 treatment.     

Reorganization of descending motor tracts in the rat spinal cord

Following lesion of the central nervous system (CNS), reinnervation of denervated areas may occur via two distinct processes: regeneration of the lesioned fibres or/and sprouting from adjacent intact fibres into the deafferented zone. Both regeneration and axonal sprouting are very limited in the fully mature CNS of higher vertebrates, but can be enhanced by neutralizing the neurite outgrowth inhibitory protein Nogo-A. This study takes advantage of the distinct spinal projection pattern of two descending tracts, the corticospinal tract (CST) and the rubrospinal tract (RST), to investigate if re-innervation of denervated targets can occur by sprouting of anatomically separate, undamaged tracts in the adult rat spinal cord. The CST was transected bilaterally at its entry into the pyramidal decussation. Anatomical studies of the RST in IN-1 antibody-treated rats showed a reorganization of the RST projection pattern after neutralization of the myelin associated neurite growth inhibitor Nogo-A. The terminal arborizations of the rubrospinal fibres, which are normally restricted to the intermediate layers of the spinal cord, invaded the ventral horn but not the dorsal horn of the cervical spinal cord. Moreover, new close appositions were observed, in the ventral horn, onto motoneurons normally receiving CST projections. Red nucleus microstimulation experiments confirmed the reorganization of the RST system. These observations indicate that mature descending motor tracts are capable of significant intraspinal reorganization following lesion and suggests the expression of cues guiding and/or stabilizing newly formed sprouts in the adult, denervated spinal cord.     

Channeling of developing rat corticospinal tract axons by myelin-associated neurite growth inhibitors.

CNS myelin contains 2 membrane proteins that are potent inhibitors of neurite growth (NI-35 and NI-250). Because myelin formation starts at different times in different regions and tracts of the CNS, this inhibitory property of myelin could serve boundary and guidance functions for late-growing fiber tracts. In the rat, the corticospinal tract (CST) grows into and down the spinal cord during the first 10 postnatal days, in close proximity to the sensory tracts fasciculus cuneatus and gracilis. Immunofluorescence for myelin constituents showed that, in the rostral half of the spinal cord, the myelinating tissue of these ascending tracts surrounds the growing, myelin-free CST in a channellike fashion. Elimination of oligodendrocytes by x-irradiation of the newborn rats, or application of antibody IN-1, which neutralizes the inhibitory substrate property of CNS myelin, resulted in significant anatomical aberration of CST fibers. In particular, the tract was larger in cross-section, and aberrant CST fibers and fascicles intermixed with the neighboring sensory ascending tracts. These results assign an important channeling and "guard-rail" function to the oligodendrocyte-associated neurite growth inhibitors for the developing CST in the rat spinal cord.     

Mice lacking L1 cell adhesion molecule have deficits in locomotion and exhibit enhanced corticospinal tract sprouting following mild contusion injury to the spinal cord

L1 is a member of the immunoglobulin superfamily of cell adhesion molecules that is associated with axonal growth, including formation of the corticospinal tract (CST). The present study describes the effects of L1 deletion on hindlimb function in locomotion, and examines the role of L1 in recovery and remodeling after contusive spinal cord injury (SCI) in mice. Uninjured adult L1 knockout (Y/-) mice had impaired performance on locomotor tests compared with their wild-type littermates (Y/+). Anterograde tracing demonstrated that CST axons project to thoracic, but not lumbar, levels of the spinal cord of Y/- mice, and revealed a diversion of these fibers from their position in the base of the dorsal columns. Retrograde tracing also revealed reduced numbers of descending projections from paraventricular hypothalamus and red nuclei to the lumbar spinal cord in Y/- mice. SCI at the mid-thoracic level produced a lesion encompassing the center of the spinal cord, including the site of the dorsal CST and surrounding gray matter (GM). The injury caused lasting deficits in fine aspects of locomotion. There was no effect of genotype on final lesion size or the growth of axons into the lesion area. However, injured Y/- mice demonstrated a robust expansion of CST projections throughout the GM of the cervical and thoracic spinal cord rostral to the lesion compared with Y/+ littermates. Thus, L1 is important for the development of multiple spinal projections and also contributes to the restriction of CST sprouting rostral to the site of a SCI in adults.     

Effects of Nogo-neutralizing antibody and neurotrophin-3 on axonal regeneration following spinal cord injury in rats

BACKGROUND： Recent studies have suggested that regeneration of the central nerve fiber following spinal cord injury occurs under specific conditions. OBJECTIVE： To study the effects of Nogo-neutralizing antibody （IN-1）, in combination with neurotrophin-3 （NT-3）, on axonal regeneration and motor function following spinal cord injury in the rat. DESIGN, TIME AND SETTING： A randomized, controlled, animal study combining immunohistochemistry was performed at the Laboratory of Neuroanatomy of Xiangya Medical College, and Central Laboratory of Xiangya the Third Hospital, Central South University from January 2006 to December 2007. MATERIALS： Eighteen healthy, Sprague Dawley rats were randomly divided into three groups, with six rats per group： control, IN-l, and IN-1/NT-3. Hemisectioned spinal cord injury models were established by cutting the posterior 2/3 of spinal cord, which is equivalent to the Ts level. METHODS： A polyethylene tubing was inserted through into subarachnoid cavity, equivalent to the superior margin at the T8 level. Saline, IN-1, and IN-1/NT-3 were respectively injected into control, IN-1, and IN-1/NT-3 groups, three times/day for seven consecutive days. MAIN OUTCOME MEASURES： At 2 weeks post-surgery, biotin dextran amine （10%） was injected into the right sensorimotor cortex area. At day 28 post-surgery, spinal cord tissue was prepared for frozen sections Positive astrocytic expression was observed with glial fibrillary acidic protein （GFAP） immunohistochemical staining whose proliferation level was represented by gray value, i.e. the higher the gray value was, the less the positive cells were, and growth of positive fibers was observed with a biotin dextran amine histological reaction. Motor function was measured according to BBB scores pre-operatively, as well as at days 1, 7, 14, 21, and 28 post-operatively. RESULTS： Three rats died during experimentation. By random supplement, a total of 18 rats were included. GFAP-positive astrocytes were observed in all the thr     

Delayed treatment with monoclonal antibody IN-1 1 week after stroke results in recovery of function and corticorubral plasticity in adult rats.

Neuronal death due to ischemic stroke results in permanent deficits in sensory, language, and motor functions. The growth-restrictive environment of the adult central nervous system (CNS) is an obstacle to functional recovery after stroke and other CNS injuries. In this regard, Nogo-A is a potent neurite growth-inhibitory protein known to restrict neuronal plasticity in adults. Previously, we have found that treatment with monoclonal antibody (mAb) IN-1 to neutralize Nogo-A immediately after stroke enhanced motor cortico-efferent plasticity and recovery of skilled forelimb function in rats. However, immediate treatment for stroke is often not clinically feasible. Thus, the present study was undertaken to determine whether cortico-efferent plasticity and functional recovery would occur if treatment with mAb IN-1 was delayed 1 week after stroke. Adult rats were trained on a forelimb-reaching task, and the middle cerebral artery was occluded to induce focal cerebral ischemia to the forelimb sensorimotor cortex. After 1 week, animals received mAb IN-1 treatment, control antibody, or no treatment, and were tested for 9 more weeks. To assess cortico-efferent plasticity, the sensorimotor cortex opposite the stroke lesion was injected with an anterograde neuroanatomical tracer. Behavioral analysis demonstrated a recovery of skilled forelimb function, and anatomical studies revealed neuroplasticity at the level of the red nucleus in animals treated with mAb IN-1, thus demonstrating the efficacy of this treatment even if administered 1 week after stroke.     

Regeneration of Lesioned Septohippocampal Acetylcholinesterase-positive Axons is Improved by Antibodies Against the Myelin-associated Neurite Growth Inhibitors NI-35/250

Two oligodendrocyte membrane proteins, NI-35 and NI-250, have been shown to be highly inhibitory for neurite growth. Upon neutralization of these components with the specific monoclonal antibody IN-1, lesioned corticospinal tract fibres were able to regenerate over long distances. In the present study, we have investigated the behaviour of regenerating cholinergic septohippocampal tract fibres. Large fimbria/fornix aspiration lesions were bridged by human amnion extracellular matrix material containing nerve growth factor, and the inhibitor-neutralizing antibody IN-1 or a control antibody were applied. After 3 - 5 weeks survival time, acetylcholinesterase (AchE)-positive fibres had crossed the bridge and, upon entering the hippocampus, had developed a profuse fibre plexus. In the controls (antibody against peroxidase) the fibre growth within the hippocampal tissue remained limited to maximally 1 mm in the caudal and lateral directions. In the presence of the antibody IN-1, however, AchE-positive fibres were seen to grow for 2 - 4 mm both in the caudal and lateral directions. Interestingly, the regenerated fibres preferably grew to their original terminal areas in the infra- and suprapyramidal layers of the hippocampus proper and the hilus, and in the supragranular layer of the dentate gyrus. These data show that the neurite growth inhibitors severely impede regenerative axon growth also for the cholinergic fibres in the hippocampus, and that their neutralization increases axon growth and leads to partial reconstitution of the original anatomical fibre distribution.     

Degeneration and sprouting of identified descending supraspinal axons after contusive spinal cord injury in the rat

Contusive spinal cord injury (SCI) results in the formation of a chronic lesion cavity surrounded by a rim of spared fibers. Tissue bridges containing axons extend from the spared rim into the cavity dividing it into chambers. Whether descending axons can grow into these trabeculae or whether fibers within the trabeculae are spared fibers remains unclear. The purposes of the present study were (1) to describe the initial axonal response to contusion injury in an identified axonal population, (2) to determine whether and when sprouts grow in the face of the expanding contusion cavity, and (3) in the long term, to see whether any of these sprouts might contribute to the axonal bundles that have been seen within the chronic contusion lesion cavity. The design of the experiment also allowed us to further characterize the development of the lesion cavity after injury. The corticospinal tract (CST) underwent extensive dieback after contusive SCI, with retraction bulbs present from 1 day to 8 months postinjury. CST sprouting occurred between 3 weeks and 3 months, with penetration of CST axons into the lesion matrix occurring over an even longer time course. Collateralization and penetration of reticulospinal fibers were observed at 3 months and were more extensive at later time points. This suggests that these two descending systems show a delayed regenerative response and do extend axons into the lesion cavity and that the endogenous repair can continue for a very long time after SCI.     

Plasticity of the corticospinal tract following midthoracic spinal injury in the postnatal rat

Rats received a midthoracic spinal cord "overhemisection" including right hemicord and left dorsal funiculus at birth (neonatal operates, N = 15) or 21 days of age (weanling operates, N = 14). In a second experiment neonatal (N = 6), 6-day (N = 3), and 12-day (N = 7) rats sustained a right sensorimotor cortex (SmI) ablation to destroy the left corticospinal tract (CST) at the same time as the spinal injury (double lesion operates). Later (3-12 months) injections of 3H-proline and autoradiography were used to label the left or right CST. The results of the first experiment showed that most right CST axons failed to grow around the spinal lesion in neonatal operates (N = 9). There was an increase in the density of label, mainly to CST projection areas, in a 1-mm zone rostral to the lesion. However, left CST axons bypassed the lesion by growing through the intact tissue in neonatal operates (N = 6). These displaced axons were consistently located within the dorsal portion of the lateral funiculus (dLF) and remained within that location caudal to the lesion, an area normally containing only a few CST axons. In spite of this abnormal position, these axons terminated bilaterally throughout the remainder of the cord in normal CST sites. In weanling operates, CST axons severed by the lesion did not regenerate around the lesion site. An increased density of label over the few spared axons within the left dLF and in CST projection zones immediately caudal to the lesion site suggested axonal sprouting by these axons. The results of the second experiment showed that the lack of growth of right CST axons around this injury in neonatal operates was, at least partially, due to an interaction with left CST axons. In neonatal double lesion operates, right CST axons grew around the spinal injury for a varying distance within the left dLF and distributed bilaterally to normal CST sites. The number of right CST axons bypassing the lesion was related to the configuration of the lesion site. A smaller number of right CST axons bypassed the lesion in 6-day double lesion operates and most terminated within 2-3 mm of the lesion site. Right CST axons failed to grow around this injury in 12-day double lesion operates.(ABSTRACT TRUNCATED AT 400 WORDS)     

Neuronal plasticity and formation of new synaptic contacts follow pyramidal lesions and neutralization of Nogo-A: a light and electron microscopic study in the pontine nuclei of adult rats

Regeneration and compensatory sprouting are limited after lesions in the mature mammalian central nervous system in contrast to the developing central nervous system (CNS). After neutralization of the growth inhibitor Nogo-A, however, massive sprouting and rearrangements of fiber connections occurred after unilateral pyramidal tract lesions in adult rats: Corticofugal fibers from the lesioned side crossed the midline of the brainstem and innervated the contralateral basilar pontine nuclei. To determine whether these newly sprouted fibers formed synaptic contacts, we analyzed the corticofugal fibers in the basilar pontine nuclei contralateral to the lesion by light and electron microscopy 2 weeks after pyramidotomy and treatment with the Nogo-A-inhibiting monoclonal antibody IN-1 (mAb IN-1). The mAb IN-1, but not a control antibody, led to structural changes in the basilar pons ipsilateral and contralateral to the lesion site. Fibers sprouted across the pontine midline and terminated topographically. They established asymmetric synaptic contacts with the characteristics of normal corticopontine terminals. These results show that adult CNS fibers are able to sprout and to form new synaptic contacts after a lesion when a growth-permissive microenvironment is provided.     

Long-term effects of methylprednisolone following transection of adult rat spinal cord.

Clinically, high-dose treatment with the glucocorticosteroid, methylprednisolone (MP), within 8 h after spinal cord injury, has been shown to improve neurological recovery. The current standard of care is to administer MP as a bolus of 30 mg/kg followed by a 23-h infusion of 5.4 mg/kg/h to spinal cord injured patients. To better understand the role of MP in neuroprotection, we have studied how MP administration affects macrophage accumulation, tissue loss, and axonal dieback at 1, 2, 4 and 8 weeks after a complete transection of the eighth thoracic spinal cord in the adult rat. A 30 mg/kg dose of MP was administered intravenously at 5 min, and 2 and 4 h after injury. The number of ED1 (antibody against microglia/macrophages) -positive cells was quantified in a 500-micrometer-wide strip of tissue directly adjacent and parallel to the transection. At all time points, MP treatment led to a significant decrease in the number of ED1-positive cells in both rostral and caudal stumps. Over the 2-month post-transection period, the average MP-induced reduction in the number of ED1-positive cells was 82% in the rostral cord stump and 66% in the caudal stump. Using a computerized image analysis system, it was observed that MP treatment resulted in a significant reduction in tissue loss in both cord stumps at 2, 4 and 8 week post-injury. Over the 2-month post-lesion period, the average MP-induced reduction in tissue loss in the caudal cord stump was higher than that in the rostral stump; 48 versus 37%, respectively. Immunostaining for neurofilaments and growth-associated protein-43 (GAP-43) revealed the presence of numerous axons near and in the lesion site. Anterograde neuronal tracing with biotinylated dextran amine showed that, in MP-treated animals, dieback of vestibulospinal fibres, but not of corticospinal fibres, was significantly diminished at all time points studied. In addition, with MP administration, 1 and 2 weeks after injury, an increase in the number of vestibulospinal fibres was found at 1 and 2 mm from the transection, suggesting transient regenerative sprouting of these fibres. The results demonstrate that treatment with MP shortly after spinal cord transection in the adult rat led to a long-term reduction of ED1-positive cells and spinal tissue loss, reduced dieback of vestibulospinal fibres, and a transient sprouting of vestibulospinal fibres near the lesion at 1 and 2 weeks post-lesion. The possible relationships between the inflammatory changes, spinal tissue sparing, and axonal survival and sprouting are complex and need to be further explored.     

Structural plasticity of the adult CNS. Negative control by neurite growth inhibitory signals

The neuronal network of the adult central nervous system (CNS) retains a limited capacity for growth and structural change. This structural plasticity has been best studied in the context of lesion-induced growth and repair. More recently, structural changes underlying functional plasticity occurring under specific physiological conditions have also been documented, in particular in the cortex and the hippocampus. Areas known for their adult plastic potential retain high levels of the growth associated protein GAP-43, suggesting a persistence of important components of the intracellular growth machinery throughout life. Interestingly, a pronounced negative correlation exists between the levels of GAP-43 and myelination in the adult CNS. Because CNS myelin contains potent neurite growth inhibitory membrane proteins, neurite growth, sprouting and plasticity were investigated in the spinal cord and brain in areas where oligodendrocyte development and myelin formation was experimentally prevented, or in the presence of an inhibitor neutralizing antibody (mAB-IN-1). In all areas, lesion-induced or spontaneous sprouting was enhanced, in parallel with persistent high levels of GAP-43. Thus, spontaneous sprouting of side branches occurred from retinal axons in the optic nerve in the absence of myelin, and target-deprived retinal axons showed increased sprouting and innervation of the contralateral optic tectum in the presence of mAB IN-1. In experimentally myelin-free spinal cords collaterals from intact dorsal roots grew over long distances to innervate deafferented target regions following the section of three dorsal roots. Similarly, the corticospinal tract sprouted across the the midline and re-established a dense plexus of fibres on the contralateral side of the spinal cord following section of one corticospinal tract in juvenile rats. Following bilateral dorsal hemisection of the spinal cord including both corticospinal tracts in young and adult rats, long distance regeneration of corticospinal fibres leading to significant functional improvements of locomotion and certain reflexes was induced by the neurite growth inhibitor neutralizing antibody IN-1.     

Identification and characterization of a cell surface marker for embryonic rat spinal accessory motor neurons

The developing mammalian spinal cord contains distinct populations of motor neurons that can be distinguished by their cell body positions, by the expression of specific combinations of regulatory genes, and by the paths that their axons take to exit the central nervous system (CNS). Subclasses of spinal motor neurons are also thought to express specific cell surface proteins that function as receptors which control the guidance of their axons. We identified monoclonal antibody (mAb) SAC1 in a screen aimed at generating markers for specific subsets of neurons/axons in the developing rat spinal cord. During early embryogenesis, mAb SAC1 selectively labels a small subset of Isl1-positive motor neurons located exclusively within cervical segments of the spinal cord. Strikingly, these neurons extend mAb SAC1-positive axons along a dorsally directed trajectory toward the lateral exit points. Consistent with the finding that mAb SAC1 also labels spinal accessory nerves, these observations identify mAb SAC1 as a specific marker of spinal accessory motor neurons/axons. During later stages of embryogenesis, mAb SAC1 is transiently expressed on both dorsally and ventrally projecting spinal motor neurons/axons. Interestingly, mAb SAC1 also labels the notochord and floor plate during most stages of spinal cord development. The mAb SAC1 antigen is a 100-kD glycoprotein that is likely to be the rat homolog of SC1/BEN/DM-GRASP, a homophilic adhesion molecule that mediates axon outgrowth and fasciculation.     

Increased corticofugal plasticity after unilateral cortical lesions combined with neutralization of the IN-1 antigen in adult rats.

If damage to the central nervous system (CNS) occurs early in life, extensive rearrangements of the remaining fiber systems as well as regeneration of lesioned fibers take place. In the rat or hamster, newly grown projections have been described only if the lesion occurred within the first two weeks postnatally. This decreasing growth ability correlates with CNS maturation and the progression of myelination. Myelin contains the potent neurite growth inhibitors NI-35/250 that are crucially involved in the failure of long-distance regeneration and the lack of compensatory structural plasticity after adult CNS lesions. In this study, we show that extensive remodeling occurs well after the termination of the growth permissive period in the adult rat if we neutralize the inhibitory properties of myelin with the monoclonal antibody IN-1. After ablation of one motor cortex and treatment with the antibody IN-1, we observed that the remaining corticospinal tract (CST) from the spared hemisphere sprouted into the denervated, contralateral red nucleus and pons. In the pons, these fibers terminated in a typical somatotopic pattern. For comparison with neonatal plasticity, we performed the same lesion in two-day-old rats (no antibody). This lesion led as well to sprouting of the remaining CST into denervated brainstem nuclei, resulting in a bilateral corticofugal projection. Our results show that neutralization of myelin-associated neurite-growth inhibitors after CNS lesions leads to a structural remodeling of the spared corticofugal fibers in adult rats, a process normally restricted to a short postnatal period.     

Selective corticospinal tract injury in the rat induces primary afferent fiber sprouting in the spinal cord and hyperreflexia

The corticospinal tract (CST) has dense contralateral and sparse ipsilateral spinal cord projections that converge with proprioceptive afferents on common spinal targets. Previous studies in adult rats indicate that the loss of dense contralateral spinal CST connections after unilateral pyramidal tract section (PTx), which models CST loss after stroke or spinal cord injury, leads to outgrowth from the spared side into the affected, ipsilateral, spinal cord. The reaction of proprioceptive afferents after this CST injury, however, is not known. Knowledge of proprioceptive afferent responses after loss of the CST could inform mechanisms of maladaptive plasticity in spinal sensorimotor circuits after injury. Here, we hypothesize that the loss of the contralateral CST results in a reactive increase in muscle afferents from the impaired limb and enhancement of their physiological actions within the cervical spinal cord. We found that 10 d after PTx, proprioceptive afferents sprout into cervical gray matter regions denervated by the loss of CST terminations. Furthermore, VGlut1-positive boutons, indicative of group 1A afferent terminals, increased on motoneurons. PTx also produced an increase in microglial density within the gray matter regions where CST terminations were lost. These anatomical changes were paralleled by reduction in frequency-dependent depression of the H-reflex, suggesting hyperreflexia. Our data demonstrate for the first time that selective CST injury induces maladaptive afferent fiber plasticity remote from the lesion. Our findings suggest a novel structural reaction of proprioceptive afferents to the loss of CST terminations and provide insight into mechanisms underlying spasticity.     

BDA皮质脊髓束神经顺行示踪在大鼠脊髓损伤模型中的应用

目的本研究采用生物素标记葡聚糖(Biotin Dextran Amine,BDA)顺行示踪技术来观察大鼠皮质脊髓束(CST)在中枢神经系统中的走行及脊髓损伤后的表现特征。方法20只雌性成年Sprague-Dawley大鼠,分为脊髓损伤组(n=10)和损伤对照组(n=10)。在相当于T7椎板水平用做好标记的显微剪刀剪断脊髓的后2/3。对照组动物术中仅咬除棘突、椎板,不切断脊髓。术后第15 d,所有动物通过立体定向开颅,将10％BDA溶液注入右侧的感觉运动区皮质内。BDA注射2周后,取出大脑和脊髓组织,采用自由漂浮法行BDA染色显影。实验动物于脊髓损伤术前、术后3d、1周、2周、4周采用Basso、Beatlie、Bresnahan(BBB)评分法测量运动功能,所得数据采用两组均数比较t检验进行统计学处理。结果1.脊髓损伤组动物双后肢瘫痪,BBB运动功能评分明显低于损伤对照组,统计学比较差异十分显著(P<0.01);2.BDA顺行示踪显示大脑皮层BDA注射区内见大脑皮层的锥体细胞及其发出的轴突呈阳性染色,BDA阳性染色的皮质脊髓束神经纤维在中脑、桥脑及延髓的腹侧面行走,但在锥体交叉后皮质脊髓束主要(约99％)在对侧脊髓白质的后索中行走。在致伤组动物中,位于脊髓白质后索中的皮质脊髓束纤维在脊髓损伤处终止;在对照组皮质脊髓束纤维染色可一直延伸至L1水平。结论BDA顺行神经