Gap junctions are intercellular channels which mediate the traffic of ions and a variety of molecular messengers between contiguous cells. Here, we report on the possibility that atypical gap junctions develop between heterologous tissues, such as regenerating nerve axons and Schwann cells, during peripheral nerve regeneration in adult rats. After a complete transection and subsequent regeneration in the rat sciatic nerve distal segment, a small scale gap junction-like structure was observed between the regenerating axons and adjoining Schwann cells. Immunoelectron microscopy showed that one of the gap junctional proteins, connexin32, was located at a small region of contact between the axon and Schwann cells. Biocytin, a small molecular weight dye, was transported from regenerating axons into adjoining Schwann cells. The present findings suggest that regenerating axons communicate directly with adjacent Schwann cells through small gap junctions, which may play a role in the mechanism of regeneration following nerve transection.
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