Morphological and Functional Evaluation of Rat Leg Muscles under the Influence of Hindlimb Unloading, Tenotomy, and Denervation

Skeletal muscle atrophy can develop under the influence of various factors associated with their disuse, such as immobilization, denervation, or exposure to microgravity. The aim of the study was to conduct a morphological and functional assessment of the soleus, gastrocnemius, and tibialis anterior muscles in models of disuse in rats. The rats were randomly divided into a control group and groups subjected to denervation, tenotomy, and hindlimb unloading (HU). During the experiments, a decrease in muscle fiber diameter was observed in all experimental groups. Tenotomy resulted in a decrease in dystrophin immunoexpression. With HU, the level of dystrophin decreased, but by day 35, recovery was observed in the gastrocnemius and tibialis anterior muscles, while in the soleus muscle, the level continued to fall. After denervation, the dystrophin content also decreased but then increased, reaching control values in the soleus muscle by day 35. The level of neuronal NO synthase decreased significantly in all experimental groups. Denervation and tenotomy lead to pronounced changes in the contractile function of the soleus muscle in rats.