Mutations in the gene for Cu/Zn superoxide dismutase (SOD1) have been detected in some families with an autosomal dominant form ofamyotrophic lateral sclerosis; these mutations appear to reduce the activity of this enzyme. To determine whether decreased SOD activity could contribute to motor neuron loss, SODi was inhibited chronically with either antisense oligodeoxynucleotides or diethyldithiocarbamate in spinal cord organotypic cultures. Chronic inhibition of SOD resulted in the apoptotic degeneration of spinal neurons, including motor neurons, over several weeks. Motor neuron loss was markedly potentiated by the inhibition of glutamate transport.In this paradigm, motor neuron toxicity could be entirely prevented by the antioxidant N-acetylcysteine and, to a lesser extent, by the non-N-methyl-D-aspartate glutamate receptor antagonist 1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-SH-2,3-benzodiazepine hydrochloride. These data support the hypothesis that the loss ofmotor neurons in familial amyotrophic lateral sclerosis could be due to a reduction in SODi activity, possibly potentiated by inefficient glutamate transport.Amyotrophic lateral sclerosis (ALS) is a motor neuron disease characterized clinically by progressive weakness, wasting of muscles, and spasticity due to the slow loss of lower motor neurons in the spinal cord and in the neocortex. Familial ALS represents 5-10o of all cases and is virtually indistinguishable clinically from the more common sporadic form. Mutations in the Cu/Zn superoxide dismutase (SOD1) gene on chromosome 21 have been detected in some families with the autosomal dominant form of familial AML (1, 2). Initial studies indicate that these mutations reduce the activity of SODi (2,3). This protein is a homodimeric metalloenzyme that catalyzes the dismutation of the superoxide anion to oxygen and hydrogen peroxide (4). Excessive levels of oxygen radicals, such as superoxide anion, have been implicated in neuronal injury, either directly or through the formation of more reactive oxygen species such as hydroxyl radicals (5-7). However, it has not been established that a chronic reduction in SODi activity diminishes the viability of spinal motor neurons. To investigate this, we have developed a model of slow toxicity in cultured organotypic spinal cord slices which combines the advantages of long-term survival with partially preserved synaptic connections (8). In this model, SOD activity was inhibited by the use of either antisense oligodeoxynucleotides (ODNs) or metal-chelating agents such as diethyldithiocarbamate (DDC), which has been shown to potentiate oxygen radical-induced toxicity in acute preparations (5).
METHODSOrganotypic Spinal Cord Cultures. Eight-day-old neonatal rat pups were decapitated, and the spinal cords were rapidly harvested and cultured (8). Culture medium, including any added pharmacological agent, was changed twice weekly. With this technique, >95% of the explants can be maintained in culture for >3 months with excellent organotypic cellular organization...