Is spinal cord isolation a good model of muscle disuse?

Abstract

The patterns of normal daily activity that are required to maintain normal skeletal muscle properties remain unknown. The present study was designed to determine whether spinal cord isolation can be used as a reliable experimental model of neuromuscular inactivity, that is, as a baseline for the absence of activity. Electromyograms (EMGs) were recorded from selected hindlimb muscles of unanesthetized rats over 24-hour periods before and 7, 30, 60, and 90 days after surgical isolation of the lumbar spinal cord. Our data indicate that some rat slow muscle fibers pre-surgery were activated for less than 3 hours per day. Spinal cord isolation (SI) reduced the mean daily integrated EMG (IEMG) and daily EMG duration in the primary slow extensor muscle (soleus) to <1% of control, and in the primary fast extensor muscles [medial gastrocnemius (MG) and vastus lateralis (VL)] to <2% of control. These parameters were decreased to <8% and 3% of control, respectively, in a primary fast flexor muscle, the tibialis anterior (TA). From 30 to 90 days post-SI, the mean amplitudes of the spontaneous EMG bursts were relatively normal in the soleus, increased approximately 2-fold in the MG and VL, and increased approximately 4-fold in the TA. Some evidence of the normal antagonistic flexor-extensor relationship was apparent in the brief periods of recorded activity post-SI. These results indicate that SI eliminates nearly all of the normal EMG activity in the hindlimb muscles in the presence of relatively normal muscle innervation and functional intraspinal neural circuitry.

Biomechanics and structural adaptations of the rat femur after hindlimb suspension and treadmill running

“…With respect to the skeletal system, tail suspension is an appropriate model for bone disuse studies, as shown by Bloomfield et al (3), who established a correlation between suspension and bone morphometry (3). An additional advantage of the model is its reversibility, which allows studies to be performed during the recovery period, in contrast to irreversible methods such as sciatic nerve division (27) and damage to the spinal cord (28). Nevertheless, some authors have also called attention to the drawbacks and limitations of the suspension model.…”

Role of MyoD in denervated, disused, and exercised muscle

“…51,52 The neuromuscular connectivity remains intact, but minimal muscular activation occurs. 92 Systemic effects may interfere with the changes induced by the lack of neural activity. Chemodenervation blocks nerve impulse conduction, while the anatomical integrity of the neuronal system remains intact.…”

Metallothionein deficiency leads to soleus muscle contractile dysfunction following acute spinal cord injury in mice

“…Spinal cord transection (SCT) was the technique employed to examine spinal cord injury-mediated muscle disuse, as numerous reports have documented the deterioration of muscle mass (MM) that occurs following this form of spinal cord injury (13,23,27,37,41). In short, the results indicate that soleus muscles obtained from spinal cord injured MT Ϫ/Ϫ animals demonstrated impaired maximal force generation per cross-sectional area (CSA) and increased lipid peroxidation, compared with muscles obtained from MT Ϫ/Ϫ surgical controls.…”