Studies on axonal regeneration in the CNS and peripheral nerves

• Main Author: Hossain-Ibrahim, Mohammed Kismet
• Published: University College London (University of London) 2007
• Subjects: 573.85
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.582542

This thesis examines the roles of inflammation and the chondroitin sulphate proteoglycan NG2 in regeneration of injured axons in the adult mammalian nervous system, against a background suggesting that inflammation around the cell bodies of axotomised neurons enhances axonal regeneration and that NG2 is a major inhibitor of CNS axonal regeneration. 1) Lipopolysaccharide was placed on / injected in motor cortex of rats, with or without concomitant injury of the cervical corticospinal tract (CST). The inflammatory response and expression of the growth-associated genes c-jun, ATF3, SCG10 and GAP-43 was investigated by immunohistochemistry or in situ hybridisation. Retrograde labelling identified CST neuron cell bodies, and anterograde tracing of CST axons identified axonal sprouting / regeneration. Lipopolysaccharide-induced inflammation promoted upregulation of GAP-43 (briefly), c-jun and SCG10 (for two weeks) in CST neurons, but did not enhance regeneration of injured CST axons. 2) Axonal regeneration was examined in the CNS and PNS of NG2 knockout mice. CNS regeneration was assessed following dorsal column injury in ascending axons with cholera toxin-conjugated horseradish peroxidase (CT-HRP) and in descending CST axons with anterograde labelling with biotinylated dextran amine (BDA), as well as transganglionic labelling of transected dorsal roots with CT-HRP. PNS regeneration after sciatic nerve crush was assessed anatomically by: retrograde labelling (from the hindpaw) of L4/5 dorsal root ganglion cells immunohistochemistry to detect sensory axons in hindpaw skin silver-cholinesterase staining of soleus motor axons / end plates EM counts of tibial and digital nerves. Functional recovery was assessed by the (motor) toe spreading reflex and (sensory) responses to von Frey hairs. There was neither anatomical nor functional evidence for significant effects on CNS or PNS axonal regeneration in the knockout mice. These findings suggest that NG2 is not a major inhibitory factor in the failure of CNS regeneration and is not important for successful axonal regeneration in the PNS.