Contractile and electrical responses of vagus-innervated frog sartorius muscles.

1. Frog sartorius muscles were transplanted to the thoracic region and re-innervated by the gastric vagus nerve. Contractile responses of the re-innervated muscles were studied. Micro-electrodes were used to measure electrical properties of the muscle fibre membrane. Histological studies of the sartorius and vagus nerves and re-innervated muscles were also carried out.2. Autonomic nerve fibres of the gastric vagus form functional connexions with the skeletal muscle fibres. Such vagus-innervated muscle fibres do not atrophy.3. Neither the contractile nor the passive electrical properties of the muscle fibres are altered by vagal innervation.4. Synaptic transmission is quantal in nature and describable by a Poisson distribution as at normal sartorius junctions. The muscle fibres, however, do show extensive multiple-innervation, and unlike normal sartorius junctions, vagus-muscle junctions have a low quantal content and show a long-lasting facilitation.5. Properties of the vagus nerve fibres apparently are not altered by synapsing with skeletal muscle fibres. They remain small diameter and have high threshold for electrical stimulation.6. The ability of these nerve and muscle fibres to influence each other is rather limited in the adult amphibian.