Alterations in cat skeletal neuromuscular junctions following prolonged inactivity.

1. The distributions of acetylcholine (ACh) receptors, cholinesterase (ChE) activity and nerve terminals were studied on cat muscle fibres which had been inactive for 2-3 years. 2. Neuromuscular junctions increased in size as a result of sprouting of terminal branches. In addition some fibres were multiply innervated at separate sites. 3. In muscles from two cats, some areas at the junction showed ChE activity but had only a relatively low density of ACh receptors. 4. The extrajunctional receptor density was higher than in normal muscles but lower than in muscles denervated for up to 10 months.