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Electron-microscopic study of the rat masseter muscle following injection of lidocaine
Abstract:
The ultrastructure of rat masseter muscle was examined at 15 min, 1 and 6 h, and 1 and 2 days following a single injection of 2% lidocaine. Lesions developed within 15 min. The plasma membrane was disrupted and invaginated. The nuclei were pyknotic and the mitochondria appeared swollen. The myofibrils separated and became disoriented. By 1 and 6 h, these changes were severe. By 1 day, the macrophages appeared in damaged myofibers. The presence of a few presumptive myoblasts signaled the onset of regeneration. By 2 days, presumptive myoblasts formed within the basement membrane. The basal lamina proved most resistant to injury. Regeneration of masseter muscle following the damage produced by lidocaine appeared discontinuous in nature. The singly nucleated presumptive myoblasts seemed to arise within the lesions.
Insights
Lidocaine causes immediate damage to rat masseter muscle, including plasma membrane disruption and mitochondrial swelling. Muscle regeneration begins within 2 days, with presumptive myoblasts forming within the resistant basal lamina.
Area of Science:
- Muscle ultrastructure
- Toxicology
- Regenerative medicine
Background:
- Lidocaine is a common local anesthetic.
- Understanding its effects on skeletal muscle is crucial for clinical applications.
- The masseter muscle's response to lidocaine injury is not well-documented.
Purpose of the Study:
- To investigate the ultrastructural changes in rat masseter muscle after lidocaine injection.
- To characterize the timeline of muscle damage and regeneration.
Main Methods:
- Rat masseter muscles were examined at various time points (15 min to 2 days) post-lidocaine injection.
- Transmission electron microscopy was used to analyze cellular and subcellular alterations.
Main Results:
- Lidocaine induced rapid ultrastructural damage, including plasma membrane disruption, nuclear pyknosis, and mitochondrial swelling.
- Myofibril separation and disorientation were observed.
- Macrophages infiltrated damaged myofibers by day 1, and presumptive myoblasts appeared, initiating regeneration.
- The basal lamina demonstrated resistance to lidocaine-induced injury.
- Regeneration appeared discontinuous, with myoblasts arising within lesions.
Conclusions:
- Lidocaine causes acute and severe damage to the masseter muscle ultrastructure.
- The basal lamina provides a scaffold for regeneration, which initiates within 2 days.
- Regeneration is a discontinuous process following lidocaine-induced muscle injury.