Motor Neuron Death Induced by Axotomy in Neonatal Mice Occurs More Slowly in a Mutant Strain in Which Wallerian Degeneration is Very Slow

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Abstract
In contrast to motor neurons of adults, motor neurons of neonatal mice die if their axons are cut. We have examined the extent, the time course and the loss of susceptibility with age to such induced death in C57BL/Wlds mice. This is a strain which has a dominant autosomal mutation which dramatically slows the rate of degeneration of axons separated from their cell bodies. Following axotomy in neonatal animals the total number of motor neurons killed is no less in C57BL/Wlds mice than in two other strains (C57BL/6J/Ola and BALB/c/Ola). Indeed, the susceptibility to axotomy persists to a later age in C57BL/Wlds mice. However, the rate of cell death is significantly slower than in the two other strains; in C57BL/Wlds mice under a week old at the time of sciatic nerve section only approximately 16% of motor neurons have been lost 3 days after axotomy, whereas in the other mice approximately 45-84% of the final loss has by then occurred. This result extends previous work which showed that retrograde degeneration of retinal ganglion cells of adult mice was slower in C57BL/Wlds mice (V. H. Perry et al., Eur. J. Neurosci., 2, 408-413, 1991). It is therefore possible that Wallerian degeneration of axons shares features in common with retrograde nerve cell death and that the Wlds mutation may throw light on aspects of this complex process.