BACKGROUND AND AIMS: The motoneurons (MNs) of the spinal cord are surrounded by perineuronal nets (PNNs) that restrict plasticity, maintain synapses and compartmentalize the neuronal surface. One of the PNN components, inhibitory to axonal growth in the injured spinal cord, is phosphacan (Pho), a chondroitin sulfate proteoglycan which binds to cell surface adhesion molecules such as L1CAM. Because L1CAM overexpression was found to promote recovery of spinal networks after injury we hypothesized that the mechanism may be through providing signals to downregulate Pho and PNNs. To evaluate the expression of Pho and response of PNNs encapsulating MNs to the injury and L1CAM overexpression in a chronic phase (5 weeks) after complete spinal cord transection. METHODS: Two groups of spinal rats (transected at Th9–10), injected with AAV5 vector carrying L1CAM or EGFP reference transgene and intact group were compared at the transcript (RTPCR) and protein (Pho immunofluorescence) level. PNNs were visualized with Wisteria floribunda agglutinin (WFA). Image analysis was performed on the longitudinal sections from the L1–2 segments acquired in confocal microscope. When analyzing PNN and Pho thickness, the perimeter of the net was taken as the point at which the most intense staining around the MN ended. Next, to focus on area of nerve terminals abutting on MNs, staining intensity of both markers was quantified in a rim around MNs limited to 2.1 mm. RESULTS: Pho around MNs formed the inner rim of PNN, occupying <50% of PNN thickness. Spinalization led to up-regulation of pho mRNA (2-fold, P<0.05) in L1–2 segments, and increased Pho protein (3-fold, P<0.05) in a rim. AAV-L1 injection decreased Pho towards controls (P<0.05) and reduced PNN thickness (by 45%), not modifying lesion-upregulated pho mRNA. CONCLUSION: L1 overexpression in spinal rats may promote MN reinnervation reducing PNNs involving Pho down-regulation. Support: NCN grants: 2013/09/B/NZ4/03306, Preludium12/05/N/ NZ4/02241.
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