Ultrastructural evidence for the lack of co-transport of B-50/GAP-43 and calmodulin in myelinated axons of the regenerating rat sciatic nerve
Abstract
Following peripheral nerve injury, neurons respond with synthesis of proteins required for axonal regeneration. Newly synthesized membrane proteins, like B-50/GAP-43, are transported with the fast component of anterograde axonal transport. Structural proteins and calmodulin are transported by the slow component. Since B-50/GAP-43 can bind calmodulin, it has been hypothesised that B-50/GAP-43 may act as a carrier for fast anterograde transport of calmodulin, so that both proteins are delivered rapidly to the distally outgrowing axons ('the fast carrier hypothesis'). We have investigated whether this hypothesis is valid in myelinated axons of the regenerating rat sciatic nerve. Seven days after crush, the nerve was ligated to accumulate fast transported proteins. Nerve pieces were dissected proximal to the ligation and processed for immunofluorescence and quantitative electron microscopy by postembedding single and double immunogold labelling. By light microscopy, we observed a qualitative increase in B-50/GAP-43 immunofluorescence in the axonal element immediately proximal to the nerve ligation (termed 'accumulated') compared to an upstream site (termed 'regenerating') closer to the cell body. The immunofluorescence for calmodul...Continue Reading
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