Changes of extracellular levels of amino acids after graded compression trauma to the spinal cord: An experimental study in the rat using microdialysis

We evaluated in rats, the time course of changes in extracellular levels of amino acids, lactate and pyruvate, which ensued spinal cord compression of mild, moderate, and severe degrees. The neurochemical findings measured by HPLC were compared with known outcome measures of this model. A laminectomy of vertebrae Th-7 and Th-8 was made and a microdialysis probe was inserted in one dorsal horn. Fluid samples were collected at intervals of 10 min. Dialysate lactate and lactate/pyruvate ratios increased in proportion to the severity of injury, suggesting a progressive derangement of energy metabolism. Mild trauma, with no neurologic deficits, did not induce any remarkable change of amino acids, but taurine values were temporarily slightly elevated. Moderate trauma, leading to transient paraparesis, resulted in a transient rise of glutamate and taurine. Severe trauma resulting in paraplegia of the hind limbs induced profound changes of extracellular amino acids. Glutamate and aspartate rose 5-6 times above basal level. There were marked elevations of taurine, glycine, arginine, alanine, asparagine, histidine, serine, threonine, and tyrosine after this degree of trauma. Glutamate, aspartate, and taurine returned to the basal level within 50 min, whereas most of the other amino acids remained elevated throughout the experiment. Thus, we found profound disturbances of extracellular amino acids and energy metabolites. The elevations of glutamate and aspartate correlated with previously recorded data on neurological outcome. The composition of the early extracellular edema showed marked temporal changes related to the severity of impact. Future studies regarding treatment of traumatic edema should focus on its chemical composition as well as its volume since such edema is not uniform in composition.