Structural Proteins at Neuromuscular Junction Are Downgraded While NRG1 and Agrin Gene Expression Increases After Muscle Injury

<b>Background/Objectives:</b> The neuromuscular junction (NMJ) is the area where peripheral nerves communicate with muscle tissue. Muscle injury can occur as part of an acute degenerative process at the NMJ. This study aims to investigate the remodeling of the NMJ after a muscle injury in an experimental model. <b>Methods:</b> We used sixty male Wistar rats divided into five groups: a control group (C) and four muscle injury groups (MI) at different time points: 0 h, 24 h, 48 h, and 7 d after injury. We subjected the right hind limb to muscle injury and dissected the gastrocnemius muscles for analysis. We employed light microscopy to examine cell nuclei and the connective tissue, immunostaining to identify and measure the pre- and postsynaptic regions as well as calcium channels (P/Q), and real-time PCR to assess the gene expression of NRG1 and Agrin. <b>Results:</b> Our findings revealed an accumulation of nuclei and connective tissue in the acute injury groups (0 to 48 h). The morpho-quantitative analyses showed that the presynaptic structures and calcium channels underwent similar remodeling due to their morpho-functional relationship. Meanwhile, the postsynaptic receptors were significantly affected by the degenerative and inflammatory processes. These results can be linked to increased expression of NRG1 and Agrin in the acute injury groups. <b>Conclusions:</b> In conclusion, the synaptic regions displayed substantial adaptations within the first 48 h, with the presynaptic region recovering rapidly and the postsynaptic region recovering slowly. This relationship suggests that significant increases in Agrin and NRG1 play a crucial role in maintaining the integrity of these structures.