Amyotrophic lateral sclerosis (ALS) is a devastating disorder of the central nervous system in middle and old age that leads to progressive loss of spinal motoneurons. Transgenic mice overexpressing mutated human Cu 2؉ ͞Zn 2؉ superoxide dismutase 1 (SOD1) reproduce clinical features of the familial form of ALS. However, changes in SOD1 activity do not correlate with severity of motor decline in sporadic cases, indicating that targets unrelated to superoxide metabolism contribute to the pathogenesis of the disease. We show here that transgenic expression in mice of GluR-B(N)-containing L-␣-amino-3-hydroxy-5-methylisoxazole-4-proprionate (AMPA) receptors with increased Ca 2؉ permeability leads to late-onset degeneration of neurons in the spinal cord and decline of motor functions. Neuronal death progresses over the entire lifespan but manifests clinically in late adulthood, resembling the course of a slow neurodegenerative disorder. Additional transgenic expression of mutated human SOD1 accelerates disease progression, aggravates the severity of motor decline, and decreases survival. These observations link persistently elevated Ca 2؉ influx through AMPA channels with progressive motor decline and late-onset degeneration of spinal motoneurons, indicating that functionally altered AMPA channels may be causally related to pathogenesis of sporadic ALS in humans.amyotrophic lateral sclerosis ͉ Ca 2ϩ permeable ion channels ͉ GluR-B gene

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To reveal whether increased Ca2+ permeability of glutamate AMPA channels triggered by the transgene for GluR‐B(N) induces decline in motor functions and neurodegeneration in the spinal cord, we evaluated growth, motor coordination, and spinal reflexes in transgenic GluR‐B(N) and wild‐type (wt) mice. To reveal whether the transgenic GluR‐B(N) expression aggravates the course of motoneuron disease in SOD1 mice, we mated heterozygous GluR‐B(N) and SOD1 [C57BL6Ico‐TgN(hSOD1‐G93A)1Gur] mice to generate double‐transgenic progeny. The phenotypic sequelae in mice carrying mutations were evaluated by monitoring growth, motor coordination, and survival. Neuronal degeneration was assessed by morphological and stereological analysis of spinal cord and brain. We found that transgenic expression in mice of GluR‐B(N)‐containing glutamate AMPA receptors with increased Ca2+ permeability leads to a late‐onset degeneration of neurons in the spinal cord and decline of motor functions. Neuronal death progressed over the entire life span, but manifested clinically in late adulthood, resembling the course of a slow neurodegenerative disorder. Additional transgenic expression of mutated human SOD1 accelerated disease progression, aggravated severity of motor decline, and decreased survival. These observations reveal that moderate, but persistently elevated Ca2+ influx via glutamate AMPA channels causes degeneration of spinal motoneurons and motor decline over the span of life. These features resemble the course of sporadic amyotrophic lateral sclerosis (ALS) in humans and suggest that modified function of glutamate AMPA channels may be causally linked to pathogenesis of ALS.

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