The present study was designed to evaluate the effect of intermittent electrical stimulation (ES) of the sciatic nerve on the expression of neuronal nitric oxide synthase (nNOS) protein in the soleus and in the medial gastrocnemius muscles 2 weeks following hindlimb suspension (HS).

In the HS+ES group, a pair of stainless steel electrodes were placed at the midportion of the unilateral sciatic nerve during hindlimb unloading. Square wave pluses with a 5 seconds ON-OFF pattern were applied to the sciatic nerve 4 hours a day for 14 days. The electrical stimulation parameters were 20 Hz, 0.3 ms, 1-5 voltage. 14 days later the sciatic nerve stimulation maximal twitch response was measured in the soleus and medial gastrocnemius muscles using an isometric tension transducer and polygraph. Western blot was used to analyze the expression of nitric oxide synthase (nNOS) protein in hindlimb muscles.

The soleus muscle consisted of slow-twitch muscle fiber and showed a prominent decrease in maximum twitch tension and muscle weight than the medial gastrocnemius muscle 2 weeks after hindlimbs suspension. Hindlimbs suspension caused a reduction in the relative quantity of nNOS protein by 89% and 55% in the soleus and the medial gastrocnemius muscles, respectively, after 2 weeks of unloading compared with the ambulatory controls. However, intermittent electrical stimulation of the sciatic nerve delayed reduction significantly with respect to the expression of nNOS protein and twitch tension during hindlimb unloading.

The results suggest that application of electrical stimulation to the sciatic nerve has a significant effect on NO signal transduction by regulating nNOS expression in atrophied hindlimb extensor muscles.