Beneficial effects of insulin-like growth factor-I on wobbler mouse motoneuron disease

Recombinant human insulin-like growth factor-I (IGF-I) is being considered as a possible therapeutic agent for the treatment of motoneuron diseases like amyotrophic lateral sclerosis. The neurological mutant mouse wobbler, carries an autosomal recessive gene (wr) and has been characterized as a model of lower motoneuron disorders with associated muscle atrophy, denervation and reinnervation. The purpose of the present study was to determine the possible beneficial effect of IGF-I administration in this mouse model. Upon diagnosis at 4 weeks of age, affected mice and their control normal littermates received human recombinant IGF-I (1 mg/kg) or vehicle solution, once a day, for 6 weeks. Body weight and grip strength were evaluated periodically during the treatment period. Mean muscle fiber diameter on biceps brachii sections, choline acetyltransferase activity in muscle extracts, and motoneuron numbers in spinal cord sections were determined. IGF-I treated wobbler mice showed a marked weight increase from 3 to 6 weeks of treatment in comparison with placebo treated mutant mice. At the end of the treatment, grip strength, estimated by dynamometer resistance, was 40% higher in IGF-I treated versus placebo treated animals. Mean muscle fiber diameter which is smaller in wobbler mice than in normal mice was increased in IGF-I treated mutants. However, in this study the muscle choline acetyltransferase activity and the number of spinal cord motoneurons were unchanged. Thus, IGF-I administration mainly results in a significant effect on the behavioral and skeletal muscle histochemical parameters of the wobbler mouse mutant.