The neuroexcitotoxic amino acids glutamate and aspartate are altered in the spinal cord and brain in amyotrophic lateral sclerosis

Abstract

Because recent studies showed a systemic defect in glutamate metabolism in amyotrophic lateral sclerosis (ALS), we measured the levels of free amino acids in frontal and cerebellar cortex and two areas of spinal cord obtained at autopsy from 22 patients who died of this disease. Glutamate levels were significantly decreased (by 21 to 40% of control values) in all areas investigated; cervical and lumbar spinal cord showed the greatest change. Aspartate levels were also significantly reduced (by 32 to 35%) in the spinal cord only. A positive correlation was shown between the changes of glutamate and aspartate as well as a significant alteration in the glutamate to glutamine ratio in the spinal cord of patients with ALS. Although we cannot exclude the possibility that these abnormalities may partly result from neuronal cell loss, the data suggest the presence of a generalized defect that may affect the neurotransmitter and metabolic pool of glutamate. The defect may be expressed more severely in the spinal cord than in other central nervous system areas. These results, taken together with the previously shown systemic abnormality, raise the possibility that distribution of glutamate between the intracellular and extracellular pool may be altered in ALS and may mediate the neurodegeneration.