Electromyography of spontaneous neuromuscular release of ACh: variations according to sex and age

Neuromuscular transmission plays a crucial role in muscle function, with differences in neurotransmitter release potentially influenced by sex and aging. While hormonal effects on neurotransmission have been studied, their impact on acetylcholine (ACh) release at the neuromuscular junction remains largely unexplored. Understanding these differences could provide insights into age-related muscle function decline and sex-specific variations in neuromuscular disorders. This study aims to investigate sex- and age-related differences in spontaneous ACh release at the neuromuscular junction in mammals, focusing on variations in electromyographic (EMG) activity. Experiments were conducted on young (2 months) and old (15 months) Swiss male and female mice. EMG recordings were taken from the gastrocnemius muscle, analyzing the percentage of sites with endplate noise, noise frequency, and spike frequency. Estrous cycle stages in female mice were identified to account for hormonal fluctuations. Males exhibited a higher percentage of sites with endplate noise than females. Old females had the highest frequency of endplate noise, while old males had the largest amplitude. Spike frequency was higher in females and increased with age. These results suggest sex and age differences in neuromuscular activity, potentially influenced by hormonal and autonomic regulation. In conclusion, neuromuscular transmission differs between sexes and across aging. Estrogens may modulate cholinergic receptor function, and autonomic nervous system activity likely contributes to observed differences. These findings highlight distinct aging patterns in neuromuscular function between males and females.