Reduced sensory neuron regeneration by C57BL/6J mice

RESUMO

The tube repair method was used to study peripheral nerve regeneration in five different inbred mouse strains. The sciatic nerve of male adult mice of the C57BL/6J,DBA/1J, C3H/HeJ, BALB/cJ and A/J strains (N=3) was cut and both proximal and distal nerve stumps were inserted into a polyethylene tube leaving a 4-mm nerve gap. After 6 weeks the tubes containing the regenerated nerve cables were processed for total myelinated axon counts. C57BL/6J mice regenerated significantly fewer myelinated axons (1024 + or - 178, mean + or - SEM) compared to the BALB/cJ (1618+ or - 64), a/j (1788 + OR - 95), dba/1j(2168 + OR - 296) OR c3h/hEj (3468 + OR - 36) strains. Horseradish peroxidase was applied 3 mm distal to be tube 4 and 40 weeks after tube implantation to further characterize the reduced regenerative response of C57BL/6J mice. Labeled sensory and somatic motor neurons were counted in the spinal cord and L4,5,6 dorsal root ganglia (DRG), respectively. Sciatic nerves from four intact C57BL/6J mice were processed in the same fashion and used as normal controls. No significant difference in the number of motor neurons was detected between the experimental (4 weeks = 663 + or - 13) animals. However, there were fewer labeled neurons in the DRG of the operated group (4 weeks = 1163 + or - 167; 40 weeks = 2574 + or - 104) compared to the control group (4211 + or - 96). These results indicated that sensory neurons are responsible for the diminished regenerative response in C57BL/6J mice after peripheral nerve transection. Neurotrophic factors may be implicated in the reduced response, although no systematic study has been done to quantify either trophic factors or their receptor synthesis in different mouse strains during Wallerian degeneration. Diminished peripheral nerve fiber regeneration makes the C57BL/6J mouse strain an ideal experimental model to evaluate the effects of exogenous substances on nerve repair