Semiquantification of fibrillation potentials with intramuscular temperature drop using an animal model

Key changes in denervated muscles and their impact on regeneration and reinnervation

The neuromuscular junction becomes progressively less receptive to regenerating axons if nerve repair is delayed for a long period of time. It is difficult to ascertain the denervated muscle's residual receptivity by time alone. Other sensitive markers that closely correlate with the extent of denervation should be found. After a denervated muscle develops a fibrillation potential, muscle fiber conduction velocity, muscle fiber diameter, muscle wet weight, and maximal isometric force all decrease; remodeling increases neuromuscular junction fragmentation and plantar area, and expression of myogenesis-related genes is initially up-regulated and then down-regulated. All these changes correlate with both the time course and degree of denervation. The nature and time course of these denervation changes in muscle are reviewed from the literature to explore their roles in assessing both the degree of detrimental changes and the potential success of a nerve repair. Fibrillation potential amplitude, muscle fiber conduction velocity, muscle fiber diameter, mRNA expression levels of myogenic regulatory factors and nicotinic acetylcholine receptor could all reflect the severity and length of denervation and the receptiveness of denervated muscle to regenerating axons, which could possibly offer an important clue for surgical choices and predict the outcomes of delayed nerve repair.

Effects of temperature on neuromuscular electrophysiology

Like nearly all biologic structures, the peripheral nervous system is remarkably temperature sensitive. Clinical neurophysiologists are most aware of the untoward effects of cooling on nerve conduction studies, including reduced conduction velocity, prolonged distal latency, and increased response amplitude and duration. However, familiarity with the effects of temperature variation on the peripheral nervous system can also provide a deeper understanding of the physiological mechanisms underlying the function of nerve, muscle, and neuromuscular junction in health and disease. Intentional temperature alteration can also improve the diagnostic accuracy of certain electrophysiologic tests, such as the use of heat when performing repetitive nerve stimulation in myasthenia gravis or the use of cold during needle electromyography in some of the myotonic disorders. Finally, extremes of temperature have long been known to produce permanent neuronal dysfunction; recent investigations are beginning to elucidate the mechanisms of such injury.