Resumo

Objectives: Amyotrophic lateral sclerosis (ALS) is a neurodegenerative and fatal human disorder characterized by progressive loss of motor neurons, clinically manifested as progressive muscular weakness, paralysis and death within 3-5 years. Approximately 10% of ALS cases are apparently of genetic origin and about 25% of those cases are caused by dominant mutations in the Cu/Zn super oxide dismutase (SOD1) gene. Transgenic mice identification of pathogenic alleles of SOD1 has led to the generation of transgenic mouse models for ALS studies. Mutant human SOD1 protein in those models leads to the development of the disease. Electrophysiology confirms the clinical diagnosis of the disease and may be used in experimental model to give insights on preclinical changes. In that model, animals show first signs at 90 days of life and the end-point is in about 125 days. For that purpose, the present study analyzed electrophysiological measurements to assess functional motoneuronal activity in transgenic mice throughout life. Our goal was to detect possible early deficits in those animals and to determine whether such deficits preceded motoneural cell loss. Methods: The colony of transgenic mice expressing the human SOD1 gene with a G93A mutation was obtained from the B6SJL-TgN (SOD1-G93A) 1Gur line (Jackson Laboratory, USA) and maintained as hemizygotes by mating transgenic males with B6SJLF1 females. Transgenic (SOD1-G93A) mice were identified by PCR amplification of DNA extracted from the tail and non-transgenic wild-type (WT) were used as controls. The animals were maintained in specific pathogen-free environment, in the biotery of the University of São Paulo Medical School. The electrophysiological measurements were recorded at 35, 50, 60, 100 and 120 days under Ketamine chorhydrate / diazepam anaesthetized. Motor unit action potentials of the gastrocnemius were recorded and distal motor latency and nerve conduction velocity were measured in the sciatic nerve. Furthermore, the electromyography recordings were made with a unipolar needle electrode (Dantec) inserted through the skin at several sites of the gastrocnemius muscle. The records of SOD1G93A animals were measured and compared with WT animals at the studied time points and treated by Student t-test. Results: The latency was noticed to be increased from day 35 (p<0.05) and progressing until 120 days (p<0.05) in the end-point of the disease in the SOD1G93A when compared with WT. The velocity of conduction was decreased in the gastrocnemius muscle of the SOD1-G93A mice from day 35 (p<0.05) compared with WT. The electromyography showed spontaneous fibrillation potentials (SFP) and positive sharp waves (PSW) characteristic of denervated myofibres in the SOD1G93A mice with 120 days in contrast with voluntary muscle action potentials (MAPs) characteristics of normal animals. Conclusion: Electrophysiological studies are important in the preclinical evaluation of ALS model and may contribute to the analysis of unraveled mechanisms in the early stage of the disease before motoneural cell loss in SOD1G93A mice.