Enzyme activity changes in rat soleus motoneurons and muscle after synergist ablation

Abstract

Quantitative enzyme histochemical methods have been used to determine the effect of ablation of synergists on the oxidative metabolism of the alpha-motoneurons and muscle fibers of the rat soleus. Sixty days postablation, the NADH-tetrazolium reductase (NADH-TR) activity of soleus motoneurons decreased 12.5% from 0.327 +/- 0.005 (mean +/- SE; optical density units) to 0.286 +/- 0.007. In the muscle fibers, the alpha-glycerophosphate dehydrogenase activity (glycolytic enzyme) decreased from 0.114 +/- 0.010 to 0.074 +/- 0.009, a change of 35.1%, and the NADH-TR activity decreased 21.2% from 0.348 +/- 0.018 to 0.274 +/- 0.017. In both the motoneurons and the muscle fibers, the decrease was nonspecific for all cells, although a greater effect on the cells with higher enzyme activity was observed. The decreased NADH-TR activity represents a shift in the oxidative profile of the motoneurons and muscle fibers, indicating a decreased ability to use oxidative metabolism for periods of short-term high-energy demands. Furthermore, the parallel decrease in muscle fibers and motoneurons with high NADH-TR activity (fast-twitch oxidative-glycolytic fibers and presumably also motoneurons) demonstrates the tight correlation of the NADH-TR activity between these parts of the motor unit in both control and synergist-ablated muscles.

Impact of volumetric muscle loss injury on persistent motoneuron axotomy

“…Motor unit reorganization has also been shown in hypertrophy inducing models of synergistic muscle ablation, indicating a slowing (i.e., more oxidative) of the muscle fiber phenotype . The current data are suggestive of altered intracellular calcium handling following VML injury due to observed differences in intrinsic contractile properties of the TA muscle.…”

“…30,31 Motor unit reorganization has also been shown in hypertrophy inducing models of synergistic muscle ablation, indicating a slowing (i.e., more oxidative) of the muscle fiber phenotype. 32 The current data are suggestive of altered intracellular calcium handling following VML injury due to observed differences in intrinsic contractile properties of the TA muscle. To that end, VML injury also induced a slowing of rates of torque production and relaxation, a significant shift of the stimulation frequency required to elicit half maximal torque, and an elevated twitch:tetani ratio, which may be due to FIGURE 5.…”

Comparison of the response of motoneurons innervating perineal and hind limb muscles to spaceflight and recovery

“…14,32,33,56 The cell body size and/or oxidative enzyme activity of spinal motoneurons have been reported to adapt to some perturbations, such as a chronic hyperthyroid state, 58 hypoxia, 34 or functional overload of the muscle via ablation of its major synergists. 47 In general, however, inactivity or reduced or elevated activity of the neuromuscular unit produced by a variety of experimental manipulations have had little effect on the cell body size and/or oxidative enzyme activity of the associated motoneurons. [11][12][13][14][15]27,40,53 Muscular adaptations to actual and simulated microgravity have been studied extensively.…”

Calcium Ion in Skeletal Muscle: Its Crucial Role for Muscle Function, Plasticity, and Disease

“…IVE). Additionally, fiber splitting paralleled by a shift of the fiber distribution toward the oxidative type I fibers has been reported (179,247,391). Many studies show that in several animal species certain forms of mechanical overload can increase muscle fiber number (10,247).…”