Neuromuscular transmission in new‐born rats

TLDR

In neonatal rats, each muscle fiber initially receives multiple synaptic inputs, but most synapses are pruned during the second week of life, leaving a single functional junction. The study proposes that the units of the end‑plate potential arise from separate nerve axons and examines this hypothesis. End‑plate potentials were recorded intracellularly from isolated phrenic/diaphragm preparations of neonatal rats during the first weeks of life. At birth, end‑plate potentials were complex, summing two to four units with distinct latencies and thresholds, but by 16–18 days they simplified to single units resembling adult muscle. Footnote markers 1–4.

Abstract

1. End‐plate potentials (e.p.p.s) were recorded intracellularly from the isolated phrenic/diaphragm preparation of the rat during the first few weeks of life. 2. Most e.p.p.s at birth were complex and resulted from the summation of two to four units, which could be separated by their different latencies and thresholds to stimulation of the phrenic nerve. 3. The e.p.p.s became simpler during the second week of the rats' life, and by 16–18 days old the e.p.p.s consisted of single units, and resembled the e.p.p.s of adult rat muscle. 4. It is proposed that the units of the e.p.p. resulted from the stimulation of separate nerve axons and that all but one of the synapses on each muscle fibre were lost during the second week of life.