Pharmacological properties, cholinesterase activity and anatomy of nerve-muscle junctions in vagus-innervated frog sartorius

Abstract

1. The pharmacological properties of the nerve-muscle junctions of vagus-innervated frog sartorius muscles were investigated. Vagus-evoked junctional potentials were ten times more sensitive to hexamethonium than were control end-plate potentials from muscles re-innervated with sartorius nerve. Hexamethonium did not affect passive electrical muscle membrane properties or quantal content. The sensitivity of vagus junctions to D-tubocurarine (dTC) did not differ from the controls.2. The amplitude and time course of vagus-evoked junctional potentials were not affected by eserine or neostigmine. Furthermore, histologically detectable acetylcholinesterase activity was not demonstrable at vagus-muscle junctions.3. The ultrastructure of vagus-innervated muscle fibres was normal in appearance indicating that the vagus was capable of structurally maintaining the muscle fibres.4. Junctional contacts were made by varicosities of unmyelinated vagal fibres. Although such varicose vagal fibres ran along the muscle fibres for long distances, they seemed to make synaptic contacts primarily at old end-plate regions, as deduced from persisting junctional folds.5. It is concluded that at least several ;trophic' factors are probably involved in the different effects of the vagus nerve on the sartorius muscle.