NEUROCHEMICAL CHANGES IN THE SPINAL-CORD IN DEGENERATIVE MOTOR-NEURONDISEASES

Human amyotrophic lateral sclerosis (ALS), a typical motor neuron dise ase, is characterized pathologically by selective degenerative loss of motoneurons in the CNS. We have demonstrated significant reductions o f neurotransmitter-related factors, such as acetylcholine-(ACh)-synthe sizing enzyme activity and glutamate and aspartate contents in the ALS , compared to the non-ALS spinal cord obtained at autopsy. We have als o shown considerable reductions in activities of cytochrome-e oxidase (CO), an enzyme contributing to aerobic energy production, and transgl utaminase (TG), a Ca2+-dependent marker enzyme for tissue degeneration , in the ALS spinal cord. We found marked increases in fragmented glia l fibrillary acidic protein (GFAP), a filamentous protein specifically associated with reactive astrocytes, in the ALS spinal cord relative to non-ALS tissue. These biochemical results corresponded well to path omor-phological neuronal degenerative loss and reactive proliferation of astroglial components in the ALS spinal cord tissue. However, these results only indicate the final pathological and biochemical outcomes of ALS, and it is difficult to follow up cause and process in the ALS spinal cord during progression of the disease. Therefore, we used an animal model closely resembling human ALS, motor neuron degeneration ( Mnd) mutant mice, a subline of C57BL/6 that shows late-onset progressi ve degeneration of lower motor neurons with paralytic gait beginning a round 6.5 mo of age, to follow the biochemical and pathological altera tions during postnatal development. We detected significant decreases in CO activity during early development and in activity of superoxide dismutase (SOD), an antioxidant enzyme, in later stages in Mnd mutant spinal cord tissue. TG activity in the Mnd spinal cord showed gradual increases during early development reaching a maximum at 5 mo, and the n tending to decrease thereafter. Amounts of fragmented GFAPs increase d continuously during postnatal development in Mnd spinal cord. These biochemical changes were observed prior to the appearance of clinical motor dysfunctions in the Mnd mutant mice. Such biochemical analyses u sing appropriate animal models will be useful for inferring the origin and progression of human ALS.