Functional recovery and increased PSA-NCAM expression following delayed administration of an anti-MAG antibody post stroke in the rat

Abstract

Stroke often renders its victims functionally impaired for long periods of time if not permanently. Inhibition of regeneration by molecules found in CNS myelin such as myelin-associated glycoprotein (MAG) and Nogo are thought to limit recovery post-stroke. We have previously demonstrated that an anti-MAG antibody, SB680949 administered 1 h post transient middle cerebral artery occlusion (tMCAO) in the rat results in improved function and neuroprotection 1. In this study we have investigated the potential time window for intervention using this antibody. In addition, we investigated expression of PSA-NCAM, a cell surface macromolecule whose expression is associated with neurogenesis and synaptic plasticity. tMCAO (90 mins) was induced in male Sprague-Dawley rats (300–350 g) as described previously 2. Two doses of SB680949 were administered intracerebroventricularly 24 hours apart, starting at 1, 6 or 24 hours following tMCAO. Control animals were dosed with IgG1 control antibody at 24 and 48 hours. Functional ability was assessed weekly using a 32 point composite neuroscore 3 and the cylinder test of forepaw placement 4. At 8 weeks, animals were deeply anaesthetised and perfused fixed with ice cold 4% paraformaldehyde and brains processed for histological assessment. Administration of SB680949 starting at 1 hour, but not at other time points, reduced lesion volume relative to animals injected with control antibody (12.3 2.1 versus 20.4 2.9 % of contralateral hemispheric volume P<0.05). Administration of SB680949 at 1 h improved function in the right (impaired) forepaw in the cylinder test at 1, 5 (P< 0.05), 7 (P< 0.01) and 8 weeks (P < 0.01). Administration of SB680949 starting at 24 h improved function in the right forepaw at 2, 5, 6 (P<0.05), 7 and 8 weeks (P<0.01). When SB680949 administration was started at 6 hours, no beneficial effect was seen in the cylinder test. SB680949 did not positively affect function as assessed by 32 point neuroscore. PSA-NCAM expression increased in the M1 region of the cortex in animals treated with SB680949 starting at 1 h(20.72.5 PSA-NCAM positive neurones in the non lesioned hemisphere of SB680949 treated animals versus 13.71.5 in the non lesioned hemisphere of control treated animals, P<0.05) and 24 hours (18.7 4.5 PSA-NCAM positive neurones in the non lesioned hemisphere of SB680949 treated animals versus 11.9 1.8 in the lesioned hemisphere of anti-MAG treated animals, P<0.05). These data confirm that early administration of SB680949 results in neuroprotection and improved function. Although when administered 24 hours post stroke anti-MAG treatment fails to offer neuroprotection, the degree of functional recovery is comparable. Increased expression of PSA-NCAM in the motor cortex in the groups displaying improved motor function supports the hypothesis that anti-MAG treatment enhances functional recovery through an increase in neurogenesis and enhanced plasticity.