Interventions to Prevent Serial Sarcomere Loss Caused by Electrical Stimulation in Rabbit Triceps Surae Muscles

Abstract

Patients with spastic Cerebral Palsy (CP) suffer from involuntary muscle contractionsdue to lesions in the brain. This appears to cause muscles to become veryshort and stiff, limiting the range of motion of a joint. This hypoextensibility maybe explained by a decrease in serial sarcomere number. It has been shown in ourlab that a 10 hour electrical stimulation period decreases serial sarcomere numbersin the triceps surae group by approximately 25%1. The rapid decrease suggests thatelectrical stimulation is a very strong regulator of serial sarcomere number. In anattempt to abolish the effects of muscle spasms, CP patients use casts or splints toprevent muscle shortening. Currently, the effect of casting on sarcomere number is notknown. Therefore, the purpose of this study is to test if casting a limb will preventsarcomere loss. In a New Zealand White Rabbit (n=1), the hind limb was placed in aplaster cast at a 70 dorsiflexion position. The leg was then stimulated via the tibialnerve (20 Hz, 4 times a-motorneuron threshold) for 10 hours. The contralateral limbserved as the control where the tibial nerve was transected to ensure no cross-overtraining effects. The Soleus, Medial Gastrocnemius (MG), Plantaris, and ExtensorDigitorum Longus (EDL) muscles were extracted and analyzed for sarcomere number.Analysis across different regions of the muscles showed a decrease of 9.67.4% in theMG, 6.96.6% in the Plantaris, 33.56.2% in the Soleus, and 4.44.1% in the EDL.No change was expected in the EDL, as it was not stimulated. The MG and Plantarisappeared to have very little decrease in serial sarcomere number, while the Soleus hada surprisingly large decrease. More experiments are required for conclusive results.