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(Accepted June 18, 1998)
The wobbler mouse suffers an autosomal recessive mutation producing severe neurodegeneration and astrogliosis in spinal cord. It has been considered a model for amyotrophic lateral sclerosis. We have studied in these animals the expression of two proteins, the growth-associated protein (GAP-43) and the NADPH-diaphorase, the nitric oxide synthesizing enzyme, employing immunocytochemistry and histochemistry. We found higher expression of GAP-43 immunoreactivity in dorsal horn, Lamina X, corticospinal tract and ventral horn motoneurons in wobbler mice compared to controls. Weak NADPH-diaphorase activity was present in control motoneurons, in contrast to intense labeling of the wobbler group. No differences in diaphorase activity was measured in the rest of the spinal cord between control and mutant mice. A group of animals received subcutaneously for 4 days a 50 mg pellet of U-74389F, a glucocorticoid-derived 21-aminosteroid with antioxidant properties but without glucocorticoid activity. U-74389F slightly attenuated GAP-43 immunostaining in dorsal regions of the spinal cord from wobblers but not in controls. However, in motoneurons of wobbler mice number of GAP-43 immunopositive neurons, cell processes and reaction intensity were reduced by U-74389F. The aminosteroid reduced by 50% motoneuron NADPH-diaphorase activity. Hyperexpression of GAP-43 immunoreactivity in wobbler mice may represent an exaggerated neuronal response to advancing degeneration or muscle denervation. It may also be linked to increased nitric oxide levels. U-74389F may stop neurodegeneration and/or increase muscle trophism and stop oxidative stress, consequently GAP-43 hyperexpression was attenuated. Wobbler mice may be important models to evaluate the use of antioxidant steroid therapy with a view to its use in human motoneuron disease.
KEY WORDS: Wobbler mouse; neurodegeneration; GAP-43; NADPH-diaphorase; 21-aminosteroids.
INTRODUCTION
The homozygous wobbler mouse (wr/wr) suffers an autosomal recessive mutation leading to severe motoneuron degeneration in brain stem and spinal cord and to pronounced astrogliosis (1,2). These animals are interesting models for amyotrophic lateral sclerosis (ALS) and infantile spinal muscular atrophy (3-5). At the structural level, signs of degeneration are found in medium and large-size A-motoneurons, while gamma motoneurons, Renshaw cells and interneurons instead show signs of sprouting (4,5). According to some authors, the astrogliosis of wobbler mice could represent a primary event, not necessarily a response to neurodegeneration (6).
In previous publications, we reported hormonal effects in the spinal cord of control and wobbler mice (79)....