Vacuolated anterior horn cells in wobbler mouse motor neuron disease: peripheral axons and regenerative capacity

We investigated whether vacuolated cervical anterior horn cells of the wobbler mouse maintain axons to the periphery, and if these morphologically abnormal neurons are capable of supporting axonal regeneration. Using retrograde axonal transport, we applied horseradish peroxidase (HRP) to peripheral nerves or muscles and with electron microscopy sought evidence for perikaryal labeling in vacuolated neurons in 23 wobbler mice. When HRP was injected into forelimb muscles, 12 of 36 vacuolated neurons became positively labeled indicating that these neurons have axons in continuity with the periphery. In regeneration studies, after nerve crush at the brachial plexus, 23 out of 85 vacuolated neurons were labeled after HRP application at the elbow level. However, after a sufficient regeneration period, none of the 36 vacuolated neurons were labeled if HRP was applied in muscles below the elbow. In all experiments, morphologically normal neurons were always labeled. Our studies indicate that some vacuolated neurons of wobbler mice not only maintain axons into the periphery, but are also capable of supporting regeneration. However, the overall function of these vacuolated neurons appears marginal compared with the majority of morphologically normal neurons in this motor neuron disease.