Locomotor Recovery in Spinal Cord-Injured Rats Treated with an Antibody Neutralizing the Myelin-Associated Neurite Growth Inhibitor Nogo-A

Abstract

The limited plastic and regenerative capabilities of axons in the adult mammalian CNS can be enhanced by the application of a monoclonal antibody (mAb), IN-1, raised against the myelinassociated neurite growth inhibitor Nogo-A. The aim of the present study was to investigate the effects of this treatment on the functional recovery of adult rats with a dorsal overhemisection of the spinal cord. Directly after injury, half of the animals were implanted with mAb IN-1-secreting hybridoma cells, whereas the others received cells secreting a control antibody (anti-HRP). A broad spectrum of locomotor tests (open field locomotor) score, grid walk, misstep withdrawal response, narrow-beam crossing) was used to characterize locomotor recovery during the 5 weeks after the injury. In all behavioral tests, the recovery in the mAb IN-1-treated group was significantly augmented compared with the control antibodytreated rats. EMG recordings of flexor and extensor muscles during treadmill walking confirmed the improvement of the locomotor pattern in the mAb IN-1-treated rats; step-cycle duration, rhythmicity, and coupling of the hindlimbs were significantly improved. No differences between the two groups with regard to nociception were observed in the tail flick test 5 weeks after the operation. These results indicating improved functional recovery suggest that the increased plastic and regenerative capabilities of the CNS after Nogo-A neutralization result in a functionally meaningful rewiring of the motor systems. Key words: spinal cord injury; functional recovery; locomotion; Nogo-A; regeneration; plasticity; ratsSpontaneous regeneration of injured axons or plastic rearrangements of spared fiber systems after spinal cord injury in mammals are very limited. The major reasons for this poor spontaneous repair capacity seem to be the insufficient growth response of neurons to injury, the growth-inhibitory components of the adult CNS tissue, and the formation of cysts and scar tissue at the injury site. Attempts to overcome local barriers by grafting peripheral nerve bridges (Cheng et al., 1996), Schwann cells (Li and Raisman, 1994;Xu et al., 1995), or olfactory ensheathing cells (Li et al., 1997;Ramon-Cueto et al., 2000) have led to regenerative fiber growth and in some instances to behavioral recovery in animal models of spinal cord injury, although the mechanistic understanding of this recovery remains incomplete because of the complexity of these interventions; Schwann cells and olfactory ensheathing glia are also important sources of trophic factors and extracellular matrix molecules (Guénard et al., 1993;Franklin and Barnett, 2000). Attempts to increase the neuronal growth response by local applications of neurotrophic factors to spinal cord injury sites have led to increased sprouting of CNS fibers and dorsal root axons (Schnell et al., 1994;Grill et al., 1997;Kobayashi et al., 1997;Liu et al., 1999;Ramer et al., 2000). In addition, neutralization of the myelin-associated neurite growth inhibitor Nogo-A (Chen et al., 2000) ...

Molecular, Anatomical, Physiological, and Behavioral Studies of Rats Treated with Buprenorphine after Spinal Cord Injury

“…Additional behavioral assays were performed, such as grid walking and the beam crossing tests, to analyze the severity of the functional deficit (Merkler et al, 2001;Cruz-Orengo et al, 2006). Briefly, in the grid-walking test, the animals were placed on a horizontal ladder (3 feet long), with bar distance alternated randomly to prevent habituation of the animal (the distance between the bars varied between 1 and 2 inches).…”

“…The beam-crossing test has been used to test the ability of a rat to balance and cross a 1 meter bar (square, 2Â2 cm; round, 2-cm diameter) at 15-18 inches from the ground (Merkler et al, 2001). The score given in this test can be up to 4 points (2 points for the square test and 2 points for the round bar test).…”

Exercise decreases myelin‐associated glycoprotein expression in the spinal cord and positively modulates neuronal growth

“…To a large extent, the failure of CNS axons to regenerate is the result of a nonpermissive environment that includes multiple factors such as formation of glial scar, deficiency in trophic factors and growth-inhibitors produced by oligodendrocytes, reactive astrocytes and fibroblasts (Domeniconi and Filbin, 2005;Fawcett and Asher, 1999;Filbin, 2003;Gage, 2000, 2002;McGee and Strittmatter, 2003;Sandvig et al, 2004;Silver and Miller, 2004). Recently, myelin-derived growth-inhibitory signals have been shown to play a major role in hampering axonal growth across the site of injury (Liebscher et al, 2005;Merkler et al, 2001). Myelin-derived proteins (Chen et al, 2000;GrandPre et al, 2000;McKerracher et al, 1994;Mukhopadhyay et al, 1994;Prinjha et al, 2000;Schwab, 2004;Wang et al, 2002) have been identified as major sources of inhibition in the injured spinal cord.…”

White matter inhibitors in CNS axon regeneration failure

“…Application of IN-1 in adult cerebellum resulted in the sprouting of uninjured Purkinje cell axon, suggesting that a normal function for such an inhibitor is to maintain the proper targeting by axonal terminals (Buffo et al, 2000). Behavior outcome such as locomotor recovery also demonstrated improvement after IN-1 application (Merkler et al, 2001). When the CST was damaged, IN-1 antibody treatment led to a doubling of the number of collaterals innervating cervical spinal cord by an undamaged fiber tract, the rubrospinal tract, which was associated with an almost complete recovery of precision movements of the forelimb and fingers ).…”