Summary and Keywords
Human spinal cord injury (SCI) results in long-lasting disabilities due to the failure of damaged neurons to regenerate. The barriers to axon regeneration in mammalian central nervous system (CNS) are so great, and the anatomy so complex that incremental changes in regeneration brought about by pharmacological or molecular manipulations can be difficult to demonstrate. By contrast, lampreys recover functionally after a complete spinal cord transection (TX), based on regeneration of severed axons, even though lampreys share the basic organization of the mammalian CNS, including many of the same molecular barriers to regeneration. And because the regeneration is incomplete, it can be studied by manipulations designed to either inhibit or enhance it. In the face of reduced descending input, recovery of swimming and other locomotor functions must be accompanied by compensatory remodeling throughout the CNS, as would be required for functional recovery in mammals. For such studies, lampreys have significant advantages. They have several large, identified reticulospinal (RS) neurons, whose regenerative abilities have been individually quantified. Other large neurons and axons are visible in the spinal cord and can be impaled with microelectrodes under direct microscopic vision. The central pattern generator for locomotion is exceptionally well-defined, and is subject to significant neuromodulation. Finally, the lamprey genome has been sequenced, so that molecular homologs of human genes can be identified and cloned. Because of these advantages, the lamprey spinal cord has been a fertile source of information about the biology of axon regeneration in the vertebrate CNS, and has the potential to serve as a test bed for the investigation of novel therapeutic approaches to SCI and other CNS injuries.
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