SPINAL-CORD REGENERATION - A PHENOMENON UNIQUE TO URODELES

Studies of neuronal survival and axonal regeneration in birds and mamm als have made it clear that the microenvironment of the CNS is critica l to the failure of CNS regeneration in these animals. This environmen t includes growth and trophic factors, ECM components and matrix turno ver enzymes, cytokines and other immune system contributions, Urodele amphibians (salamanders and newts) can regenerate spinal cord even as adults, and environmental contributions of glial populations are a maj or part of the difference between urodele and higher vertebrate spinal cord regeneration, In particular, the behavior of injury- reactive ep endymal cells (radial glia) is critical to the regenerative capacity o f urodele spinal cord. In this review we examine what is known about c ell-cell interactions between ependymal cells and neurons and between ependymal cells and other glial populations. The known contributions o f ependymal cell products such as matrix metalloproteinases and trophi c factors are discussed. There is evidence in the literature that an e pendymal response occurs during embryonic or fetal development in bird s and mammals following spinal cord transection, and this review discu sses the implications of such a process for future studies of spinal c ord injury.