Magnesium administration provokes motor unit survival, after sciatic nerve injury in neonatal rats

BACKGROUND: We examined the time course of the functional alterations in two types of muscles following sciatic nerve crush in neonatal rats and the neuroprotective effect of Mg(2+). METHODS: The nerve crush was performed on the 2(nd )postnatal day. MgSO(4)*7H(2)O was administered daily for two weeks. Animals were examined for the contractile properties and for the number of motor units of extensor digitorum longus and soleus muscles at three postnatal stages and adulthood. Four experimental groups were included in this study: i) controls, ii) axotomized rats, iii) magnesium treated controls and iv) axotomized and Mg(2+)-treated rats. RESULTS: Axotomy resulted in 20% MU survival in EDL and 50% in soleus. In contrast, magnesium treatment resulted in a significant motor unit survival (40% survival in EDL and 80% in soleus). The neuroprotective effects of Mg(2+ )were evident immediately after the Mg(2+)-treatment. Immature EDL and soleus muscles were slow and fatigueable. Soleus gradually became fatigue resistant, whereas, after axotomy, soleus remained fatigueable up to adulthood. EDL gradually became fastcontracting. Tetanic contraction in axotomized EDL was just 3,3% of the control side, compared to 15,2% in Mg(2+)-treated adult rats. The same parameter for axotomized soleus was 12% compared to 97% in Mg(2+)-treated adult rats. CONCLUSIONS: These results demonstrate that motoneuron death occurs mostly within two weeks of axotomy. Magnesium administration rescues motoneurons and increases the number of motor units surviving into adulthood. Fast and slow muscles respond differently to axotomy and to subsequent Mg(2+ )treatment in vivo

Eletroestimulação seletiva mantem estrutura e função do tibial anterior desnervado de ratos Structure and function of denervated tibialis anteriores are maintained by electrical stimulation in rats

OBJETIVO: A eletroestimulação para tratamento de músculos desnervados deve ser aplicada através do tratamento seletivo. Este estudo avaliou o efeito da eletroestimulação seletiva do músculo desnervado sobre sua estrutura e função. MÉTODOS: Foram utilizados cinqüenta ratos Wistar distribuídos em controle, desnervado estimulado e desnervado não-estimulado. Após avaliação eletrodiagnóstica de estímulo pré-desnervação, os animais sofreram desnervação proximal completa do músculo tibial anterior unilateral. Houve reavaliação semanal para adaptação dos parâmetros de tratamento seletivo, aplicado três vezes por semana. Os animais foram mortos após 7, 14, 28 e 56 dias do pós-cirúrgico. Foram realizados procedimentos histoquímicos e estudos morfológicos e morfométricos. RESULTADOS: Os animais desnervados estimulados não apresentaram contratura da articulação do tornozelo e não houve automutilações nas patas. Alterações significativas nas áreas das fibras musculares tipo IIB (desnervados estimulados aos 7 dias) e tipo IIA e híbridas (desnervados estimulados 28 e 56 dias) indicaram menor atrofia. Transição do tipos de fibras musculares foi significativa, indicando uma manutenção do padrão funcional do músculo tibial anterior nos períodos de 7 e 14 dias. CONCLUSÃO: Conclui-se que houve manutenção temporária da estrutura e função do músculo tibial anterior desnervado através da eletroestimulação seletiva.<br>OBJECTIVE: Electrical stimulation for treatment of denervated muscles should be implemented by selective treatment. This study evaluated the effect of selective electrical stimulation on the structure and function of denervated muscle. METHODS: Fifty Wistar mice were allocated to control, stimulated denervated and non-stimulated denervated groups. Following an electrodiagnostic evaluation, the animals underwent complete unilateral denervation of the proximal anterior tibialis muscle. Weekly re-assessment was carried out in order to adjust the parameters of the selective treatment, applied three times a week. The animals were sacrificed at 7, 14, 28 and 56 days after undergoing the surgical procedures. Histochemical procedures and morphologic and morphometric studies were carried out. RESULTS: The denervated stimulated animals did not present contracture of the ankle joint and self-mutilation was not found on the feet. Significant alterations around the type IIB (denervated stimulated at 7 days), type IIA and hybrid (denervated stimulated at 28 and 56 days) fibers showed less atrophy. The transition of muscle fibers types was significant, indicating the preservation of the functional pattern of the anterior tibialis muscle at 7 and 14 days. CONCLUSION: We found that the selective electrical stimulation was able to temporarily maintain the structure and function of the denervated anterior tibialis muscle