An investigation into the involvement of cell adhesion molecules and perineurial cells in endogenous tissue repair following experimental spinal cord injury in the rat

Since the beginning of the last century, it is widely accepted that the devastating consequences of spinal cord injury are due to the failure of lesioned CNS axons to regenerate. In the past 20 years, considerable progress has been made in understanding the cellular and molecular mechanisms that contribute to the lack of successful regeneration of lesioned CNS axons. To date, however, relatively little is known about endogenous tissue repair processes which occur during the first weeks after spinal cord injury. The aim of the present study was to investigate novel aspects of the cellular and molecular interactions that take place during attempted endogenous tissue repair following experimental spinal cord injury in the rat.The first part of the investigation demonstrates, for the first time, the expression of the cell adhesion molecules L1 and N-CAM during extensive cellular invasion into the lesion site following dorsal hemisection of the rat spinal cord. This thesis will show that the invasion of the lesion site by non-neuronal cells and the distinct directionality, displayed by many of the cellular and axonal components within the lesion site are associated with a strong and long-lasting expression of the cell adhesion molecules L1 and N-CAM. The non-neuronal cells within the lesion site rapidly formed a framework with an overall longitudinal orientation which subsequently became associated with in-growing nerve fibres. Using double immunofluorescence, it was possible to identify Schwann cells and leptomeningeal cells contributing to the pattern of cell adhesion molecule expression within the lesion. Many of the regenerating nerve fibres entered the lesion site from both the rostral and caudal intact spinal cord. At the lesion interface, these axons passed through regions of intimately intermingled and longitudinally orientated processes of reactive astrocytes and Schwann cells/leptomeningeal cells. In the second part of the investigation, immunohistochemistry for the detection of epithelial membrane antigen (EMA) was performed in an attempt to identify perineurial cells in the lesion site after compression injury of the rat spinal cord. Similar to Schwann cells, perineurial cells are components of peripheral nerves and known to play an important role during peripheral nerve regeneration. This behaviour led to the notion that perineurial cells or perineurial-like cells of the spinal nerve roots might also participate in the re-organisational events taking place after spinal cord injury. In the present investigation EMA-immunoreactivity was detectable in unlesioned and lesioned spinal nerve roots but not in the unlesioned spinal cord. In the lesioned spinal cord, EMA-positive cells were detectable as early as 14 days p.o. Surprisingly, neither the distribution of the stained profiles in the nerve roots, nor the morphology of the immunoreactive cells in the roots and in the lesion site resembled that of perineurial cells. Therefore, additional investigations, including double immunofluorescence with a range of antibodies, were performed. These studies led to the conclusion that, under the present experiment conditions, the anti-EMA antibody was identifying myelin-forming Schwann cells rather than perineurial cells