Analysis of Changes in Parameters of Neuromuscular Synaptic Transmission in Mice During Early Postnatal Ontogeny

The intercellular contact between a motor neuron and a skeletal muscle fiber is a common model for electrophysiological studies of the mechanisms underlying chemical synapse function. However, data on the features of the neuromuscular synaptic transmission process in animals during early postnatal development are extremely scarce, and no systematic study of changes in electrophysiological parameters during ontogeny has been conducted. Using a relatively recently proposed model, namely the mouse m. levator auris longus neuromuscular preparation, and the classical method of muscle fiber dissection used to block contractions, we performed for the first time a detailed analysis of the most frequently used electrophysiological parameters characterizing the processes of spontaneous and evoked quantal acetylcholine release from motor nerve endings: amplitude-temporal parameters of spontaneous and evoked endplate potentials, miniature endplate potential frequency, quantal content, and latency of evoked responses. We described the dynamics of changes in the recorded parameters throughout the entire period of the mouse life. Particularly pronounced changes were identified precisely in the first days after birth, but it also turned out that neuromuscular signaling in two-week-old animals still differs significantly from that in the synapse of a sexually mature organism in a number of parameters. The obtained data can be used in the future to study the ontogenetic features of various neuroregulatory processes.