Repairing the nervous system

Abstract

The winter meeting of the Anatomical Society, on the subject of ‘Repairing the nervous system’, was held at the Royal Holloway College from 7th to 9th January 2003. The organisers focused on reviewing the current status of ideas about the cellular mechanisms involved in both stimulating and preventing CNS repair. We need to try to understand the complexity of environment through which regenerating axons have to grow, and how this abnormal situation compares with the normal process of navigation in development. Critically, we need to understand how successfully cells respond to these challenges by changing gene expression to generate new or recapitulate old programs for axonal growth and navigation. A major issue is how the environment of the CNS limits repair and how we can try to devise strategies to overcome these limitations and enhance the repair process. This may involve the use of strategies to reverse negative influences of glial cells on axonal regeneration, or the transplantation of cells to promote the regeneration process. This was an excellent meeting, with many stimulating presentations which reviewed cellular and molecular approaches to CNS repair. Some of these talks are presented in this volume and hopefully give an overview of some of the major issues and approaches being used to stimulate CNS repair. John Nicholls reviewed the work on spinal cord regeneration, which has used an elegant in vitro model system from the marsupial and now complemented these cellular approaches with an investigation into differential gene expression during regeneration. Susanna Blackshaw highlighted the beauty of the leech CNS as a model for studying neuronal regeneration in identified neurones. Her recent work shows how this relatively simple model organism can be used to generate a wealth of information on the changes in neuronal gene expression during the regeneration process, and how this data will inform studies of CNS repair in both invertebrate and vertebrates. Jeremy Taylor reviewed the advantages of using immature animals for studying CNS repair, and how the major limitation for successful repair at these stages is trophic support. To overcome this obstacle, glial cells in the peripheral and central nervous system are being studied, and are shown to provide novel factors which act with well studied neurotrophins to stimulate regeneration. James Fawcett discussed the roles of chondroitin sulphate proteoglycans in limiting both CNS regeneration at glial scars and also the more widespread phenomenon of neuronal plasticity. This exciting field has revealed unexpected controls on neuronal plasticity and has shown how these inhibitory mechanisms could be harnessed to promote CNS repair. Marie Filbin demonstrated the remarkable change in neuronal response to CNS myelin that occurs during maturation of the CNS. Again, an understanding of the cellular mechanisms that control these responses has opened a window for overcoming these limiting factors. The negative inhibitory response that myelin proteins have on regenerating axons, can be reversed to a positive growth enhancing response. Susan Barnett has studied the use of the special glial cells, the olfactory ensheathing cells that allow continual renewal of the olfactory system throughout life, in transplants to the CNS. Her careful studies on the preparation, purification and behaviour of these cells when grafted into the CNS highlight the importance of understanding the cell biology underpinning the use of transplanted cells for CNS repair.