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Notes: Clinically, high-dose treatment with the glucocorticosteroid, methylprednisolone (MP), within 8 h after spinal cord injury, has been shown to improve neurological recovery. The current standard of care is to administer MP as a bolus of 30 mg/kg followed by a 23-h infusion of 5.4 mg/kg/h to spinal cord injured patients. To better understand the role of MP in neuroprotection, we have studied how MP administration affects macrophage accumulation, tissue loss, and axonal dieback at 1, 2, 4 and 8 weeks after a complete transection of the eighth thoracic spinal cord in the adult rat. A 30 mg/kg dose of MP was administered intravenously at 5 min, and 2 and 4 h after injury. The number of ED1 (antibody against microglia/macrophages) -positive cells was quantified in a 500-μm-wide strip of tissue directly adjacent and parallel to the transection. At all time points, MP treatment led to a significant decrease in the number of ED1-positive cells in both rostral and caudal stumps. Over the 2-month post-transection period, the average MP-induced reduction in the number of ED1-positive cells was 82% in the rostral cord stump and 66% in the caudal stump. Using a computerized image analysis system, it was observed that MP treatment resulted in a significant reduction in tissue loss in both cord stumps at 2, 4 and 8 week post-injury. Over the 2-month post-lesion period, the average MP-induced reduction in tissue loss in the caudal cord stump was higher than that in the rostral stump; 48 versus 37%, respectively. Immunostaining for neurofilaments and growth-associated protein-43 (GAP-43) revealed the presence of numerous axons near and in the lesion site. Anterograde neuronal tracing with biotinylated dextran amine showed that, in MP-treated animals, dieback of vestibulospinal fibres, but not of corticospinal fibres, was significantly diminished at all time points studied. In addition, with MP administration, 1 and 2 weeks after injury, an increase in the number of vestibulospinal fibres was found at 1 and 2 mm from the transection, suggesting transient regenerative sprouting of these fibres. The results demonstrate that treatment with MP shortly after spinal cord transection in the adult rat led to a long-term reduction of ED1-positive cells and spinal tissue loss, reduced dieback of vestibulospinal fibres, and a transient sprouting of vestibulospinal fibres near the lesion at 1 and 2 weeks post-lesion. The possible relationships between the inflammatory changes, spinal tissue sparing, and axonal survival and sprouting are complex and need to be further explored.

Notes: Summary RN33B, a conditionally-immortalized neuronal cell line, survives and differentiates following grafting into the neocortex and hippocampus of adult and neonatal rat hosts. We have previously shown that these cells assume shapes characteristic of endogenous neurons at the integration site and persist up to 24 weeks post-grafting. In the present study we use electron microscopy and immunohistochemistry to characterize such cells. Differentiated RN33B cells were identical in size to endogenous neurons and their sizes depended on the specific location of integration. RN33B cells in the granule cell layer of the dentate gyrus and CA3 and CA1 pyramidal layers were 9.0, 15.3, and 12.6 μm in diameter, respectively. Grafted RN33B cells received synapses from fibres of host origin. Differentiated cells expressed neuronal markers, but not glial markers. Some differentiated cells expressed glutamate bothin vitro andin vivo whereas undifferentiated cells did not. Grafted RN33B cells that differentiated with morphologies similar to CA3 pyramidal neurons and pyramidal cortical neurons expressed Py antigen, a neuronal marker that is differentially expressed in endogenous large pyramidal neurons of the cerebral cortex and large pyramids of hippocampal field CA3. This Py immunoreactivity was region-specific and corresponded to the endogenous pattern of Py immunostaining. Collectively, these data indicate that RN33B cells are capable of region-specific differentiation and have the potential to integrate functionally into the host CNS.