In Vivo Assays

In vivo studies regarding PNS regeneration most often rely on a rat sciatic nerve transection model. The sciatic nerve runs from the back to the lower limbs and provides motor and sensory function to the limb. Transecting this nerve eliminates motor and sensory function. Without surgical repair of the transected nerve, spontaneous regeneration is rare (Panseri et al. 2008). NGC materials have been evaluated by implanting a cuff around a transected nerve and suturing the severed ends of the nerve fiber bundle in place (Belkas et al. 2004; Hudson et al. 2000; Bunge 2001; Huang and Huang 2006). Without sacrificing the animal, motor and sensory recovery can be evaluated and characterized in a variety of ways, including a walking track test and Von-Frey test (Yannas and Hill 2004; Panseri et al. 2008). Electrophysiological data, specifically the compound motor action potential and compound sensory action potential amplitudes, reveal the degree to which muscle and digital sensory nerves have been reinnervated (Archibald et al. 1995). Functional motor and sensory recovery is the ultimate goal of any treatment and is indicative of tissue regeneration. Motor and sensory functions rarely recover without appreciable tissue regeneration. Sacrificing the animal and performing histology studies on the sciatic nerve and surrounding tissue can provide more detailed information regarding protein and cellular activity and tissue regeneration. If the NGC was implanted to bridge a tissue gap between the severed ends of the nerve fiber bundle, the cross-sectional area of the tissue growing to fill the gap can be evaluated along the length of the NGC (Williams et al. 1993). The number of nerve fibers, fiber diameter, density of axons, number of unmyelinated or myelinated axons, the thickness of myelin sheath, Schwann cell populations, collagen IV deposition, and degree of vascularization are all indicators of tissue regeneration which can be evaluated by tissue staining (Mackinnon et al. 1991; Gordon et al. 2005; Panseri et al. 2008). Immunohistochemistry techniques to evaluate reactive gliosis in the CNS include the labeling of GFAP and also vimentin, proteins expressed in reactive astrocytes (Silver and Miller 2004).

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