Etude de la régénération nerveuse périphérique post-traumatique avec perte de substance chez les rats (mise au point et évaluation de procédés de guidage implantables et stratégies pharmacologiques)

[ ] Ces stratégies visent à être complémentaires, dans l optique d une thérapie alternative à l autogreffe. Nos résultats ont montré pour la première fois que le FK506 et la vitamine D favorisent la myélinisation et la maturation physiologique des fibres nerveuses périphériques axotomisées. De plus, la vitamine D augmente l axogenèse, la récupération fonctionnelle des fibres nerveuses métabosensitives et diminue la perte axonale. Concernant les matériaux implantables, nous montrons que les tuteurs nerveux limitent la perte axonale. De plus, ce type de guide entraîne des récupérations fonctionnelles identiques à l autogreffe. Toutefois, le muscle squelettique dénaturé reste insatisfaisant. Ces résultats démontrent que le tuteur nerveux collagénique que nous avons mis au point constitue une alternaticve efficace à l'autogreffe nerveuse. Parralèlement, la vitamine D possède des propriètés de neuroprotection et de neurorégénération qui permettraient, en association avec l'implantation du tuteur, d'envisager des récupérations au-delà des valeurs de l'autogreffe. D'autres études sont envisagées mettant en jeu l'intégration d'une matrice de guidage au sein du tuteur.[ ] We show here that the collagen nerve guide 1) limits the axonal loss an 2) induces a functional recovery in a similar way to the ANG. Conversely, the denatured skeletal muscle cannot be considered as a relevant alternative. With respect to our tested pharmacological compounds, we show here that both FK506 and vitamin D promote myelination and physiological maturation of axotomized peripheral nerve fibers. On the one hand, vitamin D signicantly 1) increases axogenesis and functional recovery of metabosensitive nerve fibers and 2) reduces axon degeneration. On the other hand, FK506 potentiates functional recovery of metabosensitive fibers. We can conclude that the collagen nerve guide used in this study is an alternative to ANG technique. However, further studies are warranted ti improve the collagen conduit. We plant to insert a guidance matrix into the guide. in order to avoid confounding factors, physical and pharmacological strategies were assessed separately. In the future, they could be combined with the aim of achieving a more complete structural and functional recovery.AIX-MARSEILLE2-BU Sci.Luminy (130552106) / SudocSudocFranceF

Neuromuscular rehabilitation by treadmill running or electrical stimulation after peripheral nerve injury and repair.

Numerous studies have been devoted to the regeneration of the motor pathway toward a denervated muscle after nerve injury. However, the regeneration of sensory muscle endings after repair by self-anastomosis are little studied. In previous electrophysiological studies, our laboratory showed that the functional characteristics of tibialis anterior muscle afferents are differentially affected after injury and repair of the peroneal nerve with and without chronic electrostimulation. The present study focuses on the axonal regeneration of mechano- (fibers I and II) and metabosensitive (fibers III and IV) muscle afferents by evaluating the recovery of their response to different test agents after nerve injury and repair by self-anastomosis during 10 wk of treadmill running (LSR). Data were compared with control animals (C), animals with nerve lesion and suture (LS), and animals with lesion, suture, and chronic muscle rehabilitation by electrostimulation (LSE) with a biphasic current modulated in pulse duration and frequency, eliciting a pattern mimicking the activity delivered by the nerve to the muscle. Compared with the C group, results indicated that 1) muscle weight was smaller in LS and LSR groups, 2) the fatigue index was greater in the LS group and smaller in the LSE group, 3) metabosensibility remained altered in the LS and LSE groups, and 4) mechanosensitivity presented a large increase of the activation pattern in the LS and LSE groups. Our data indicated that chronic muscle electrostimulation partially favors the recovery of muscle properties (i.e., muscle weight and twitch response were close to the C group) and that rehabilitation by treadmill running also efficiently induced a better functional muscle afferent recovery (i.e., the discharge pattern was similar to the C group). The effectiveness of the chronic electromyostimulation and the treadmill exercise on afferent recovery is discussed with regard to parameters listed above

Delayed Injection of a Physically Cross-Linked PNIPAAm- g -PEG Hydrogel in Rat Contused Spinal Cord Improves Functional Recovery

International audienc

Metabosensitive afferent fiber responses after peripheral nerve injury and transplantation of an acellular muscle graft in association with schwann cells.

Studies dedicated to the repair of peripheral nerve focused almost exclusively on motor or mechanosensitive fiber regeneration. Poor attention has been paid to the metabosensitive fibers from group III and IV (also called ergoreceptor). Previously, we demonstrated that the metabosensitive response from the tibialis anterior muscle was partially restored when the transected nerve was immediately sutured. In the present study, we assessed motor and metabosensitive responses of the regenerated axons in a rat model in which 1 cm segment of the peroneal nerve was removed and immediately replaced by an autologous nerve graft or an acellular muscle graft. Four groups of animals were included: control animals (C, no graft), transected animals grafted with either an autologous nerve graft (Gold Standard-GS) or an acellular muscle filled with Schwann Cells (MSC) or Culture Medium (MCM). We observed that (1) the tibialis anterior muscle was atrophied in GS, M(SC) and M(CM) groups, with no significant difference between grafted groups; (2) the contractile properties of the reinnervated muscles after nerve stimulation were similar in all groups; (3) the metabosensitive afferent responses to electrically induced fatigue was smaller in M(SC) and MCM groups; and (4) the metabosensitive afferent responses to two chemical agents (KCl and lactic acid) was decreased in GS, M(SC) and M(CM) groups. Altogether, these data indicate a motor axonal regeneration and an immature metabosensitive afferent fiber regrowth through acellular muscle grafts. Similarities between the two groups grafted with acellular muscles suggest that, in our conditions, implanted Schwann cells do not improve nerve regeneration. Future studies could include engineered conduits that mimic as closely as possible the internal organization of uninjured nerve

Examination of the combined effects of chondroitinase ABC, growth factors and locomotor training following compressive spinal cord injury on neuroanatomical plasticity and kinematics.

While several cellular and pharmacological treatments have been evaluated following spinal cord injury (SCI) in animal models, it is increasingly recognized that approaches to address the glial scar, including the use of chondroitinase ABC (ChABC), can facilitate neuroanatomical plasticity. Moreover, increasing evidence suggests that combinatorial strategies are key to unlocking the plasticity that is enabled by ChABC. Given this, we evaluated the anatomical and functional consequences of ChABC in a combinatorial approach that also included growth factor (EGF, FGF2 and PDGF-AA) treatments and daily treadmill training on the recovery of hindlimb locomotion in rats with mid thoracic clip compression SCI. Using quantitative neuroanatomical and kinematic assessments, we demonstrate that the combined therapy significantly enhanced the neuroanatomical plasticity of major descending spinal tracts such as corticospinal and serotonergic-spinal pathways. Additionally, the pharmacological treatment attenuated chronic astrogliosis and inflammation at and adjacent to the lesion with the modest synergistic effects of treadmill training. We also observed a trend for earlier recovery of locomotion accompanied by an improvement of the overall angular excursions in rats treated with ChABC and growth factors in the first 4 weeks after SCI. At the end of the 7-week recovery period, rats from all groups exhibited an impressive spontaneous recovery of the kinematic parameters during locomotion on treadmill. However, although the combinatorial treatment led to clear chronic neuroanatomical plasticity, these structural changes did not translate to an additional long-term improvement of locomotor parameters studied including hindlimb-forelimb coupling. These findings demonstrate the beneficial effects of combined ChABC, growth factors and locomotor training on the plasticity of the injured spinal cord and the potential to induce earlier neurobehavioral recovery. However, additional approaches such as stem cell therapies or a more adapted treadmill training protocol may be required to optimize this repair strategy in order to induce sustained functional locomotor improvement

Convenient access to biocompatible block copolymers from SG1-based aliphatic polyester macro-alkoxyamines.

International audienceSG1-based poly(d,l-lactide) (PLA) or poly(epsilon-caprolactone) (PCL) macro-alkoxyamines were synthesized and further used as macroinitiators for nitroxide-mediated polymerization (NMP) of 2-hydroxyethyl (meth)acrylate (HE(M)A) to obtain the corresponding PLA- or PCL-PHE(M)A block copolymers. First, a PLA-SG1 macro-alkoxyamine was prepared by 1,2-intermolecular radical addition (IRA) of the MAMA-SG1 (BlocBuilder) alkoxyamine onto acrylate end-capped PLA previously prepared by ring-opening polymerization. The NMP of HEA monomer from the PLA-SG1 macro-alkoxyamine appeared to be well controlled in the presence of free SG1 nitroxide, contrary to that of HEMA. In the latter case, adjustable molecular weights could be obtained by varying the HEMA to macro-alkoxyamine ratio. The versatility of our approach was then further applied to the preparation of PHEMA-b-PCL-b-PHEMA copolymers from a alpha,omega-di-SG1 functionalized PCL macro-alkoxyamine previously obtained from a PCL diacrylate by IRA. Preliminary studies of neuroblast cultures on these PCL-based copolymer films showed acceptable cyto-compatibility, demonstrating their potential for nerve repair applications

Functional recovery after peripheral nerve injury and implantation of a collagen guide.

Although surgery techniques improved over the years, the clinical results of peripheral nerve repair remain unsatisfactory. In the present study, we compare the results of a collagen nerve guide conduit to the standard clinical procedure of nerve autografting to promote repair of transected peripheral nerves. We assessed behavioral and functional sensori-motor recovery in a rat model of peroneal nerve transection. A 1cm segment of the peroneal nerve innervating the Tibialis anterior muscle was removed and immediately replaced by a new biodegradable nerve guide fabricated from highly purified type I+III collagens derived from porcine skin. Four groups of animals were included: control animals (C, n=12), transected animals grafted with either an autologous nerve graft (Gold Standard; GS, n=12) or a collagen tube filled with an acellular skeletal muscle matrix (Tube-Muscle; TM, n=12) or an empty collagen tube (Collagen-Tube; CT, n=12). We observed that 1) the locomotor recovery pattern, analyzed with kinetic parameters and peroneal functional index, was superior in the GS and CT groups; 2) a muscle contraction was obtained in all groups after stimulation of the proximal nerve but the mechanical muscle properties (twitch and tetanus threshold) parameters indicated a fast to slow fiber transition in all operated groups; 3) the muscular atrophy was greater in animals from TM group; 4) the metabosensitive afferent responses to electrically induced fatigue and to two chemical agents (KCl and lactic acid) was altered in GS, CT and TM groups; 5) the empty collagen tube supported motor axonal regeneration. Altogether, these data indicate that motor axonal regeneration and locomotor recovery can be obtained with the insertion of the collagen tube RevolNerv. Future studies may include engineered conduits that mimic as closely as possible the internal organization of uninjured nerve

FK506 Induces Changes in Muscle Properties and Promotes Metabosensitive Nerve Fiber Regeneration

International audienceAbstract Accumulating evidence indicates that in addition to its immunosuppressant properties, FK506 (tacrolimus), an FDA-approved molecule, promotes nerve regeneration. However, the neuroprotective and neurotrophic effects of this molecule on sensitive fiber regeneration have never been studied. In order to fill this gap in our knowledge, we assessed the therapeutic potential of FK506 in a rat model of peripheral nerve repair. A 1-cm segment of left peroneal nerve was cut out and immediately autografted in an inverted position. After surgery, the animals were treated with FK506 (1.2 mg/kg/d) via an osmotic pump and compared to untreated animals. Recovery of use of the injured leg was assessed weekly for 12 weeks using a walking track apparatus and a camcorder. At the end of this period, motor and metabosensitive responses of the regenerated axons were recorded and histological analysis was performed. We observed that FK506 significantly: (1) increased the diameter of regenerated axons in the distal portion of the graft; (2) improved the responses of sensory neurons to metabolites such as potassium chloride and lactic acid; and (3) induced a fast-to-slow-fiber-type transition of the tibialis anterior muscle. Taken together, these data indicate that FK506 potentiates metabosensitive nerve fiber regeneration. Pharmacological studies of various dosages and concentrations of FK506 are required before recommending this drug for therapeutic treatment of nerve injuries