Contractile and electrical responses of vagus‐innervated frog sartorius muscles

Abstract

SUMMARY1. 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.

The physiology, pharmacology, and trophic effectiveness of synapses formed by autonomic preganglionic nerves on frog skeletal muscle.

“…Interestingly, vagus-reinnervated frog muscles showed facilitation at 1/sec. (Landmesser, 1971), a rate that is significantly slower than that in almost all s.p.n.-reinnervated fibres studied here. McLachlan (1975), in a more recent analysis of guinea-pig ganglionic junctions, described two components of facilitation.…”

“…It has long been known that denervated skeletal muscle can be reinnervated by nerves that release acetylcholine (ACh), even if they normally terminate on other tissues (Langley & Anderson, 1904;Beattie, Duel & Ballance, 1932;Hillarp, 1946;Brown & Satinsky, 1951;Guth & Frank, 1959;Landmesser, 1971Landmesser, , 1972Ramirez & Luco, 1973;Bennett, McLachlan & Taylor, 1973). In addition, there have been reports of successful, apparently cholinergic, reinnervation by nerves whose normal transmitter is unknown, such as the central ends of spinal sensory nerves (Weiss, 1935) and the central ends of vagal sensory afferents (Vera & Luco, 1967).…”

The formation of synapses in reinnervated and cross‐reinnervated adult avian muscle

“…The pattern of reinnervation of mature muscle does not seem to be dependent on the kind of nerve supply, as reinnervation with preganglionic nerves of either the frog sartorius (Landmesser, 1971(Landmesser, , 1972 or the mammalian diaphragm (McLachlan, Taylor & Bennett, 1972) simply reconstitutes the normal innervation pattern of those muscles. Thus each sartorius muscle fibre is innervated at two points oil its surface and in the diaphragm the innervation occurs at a single point in the middle of the fibres.…”

Channel gating at frog neuromuscular junctions formed by different cholinergic neurones.

“…It is well known that preganglionic autonomic neurones transplanted onto denervated skeletal muscle will form functioning neuromuscular synapses (Langley & Anderson, 1904;Brown & Satinsky, 1951;Landmesser, 1971Landmesser, , 1972Ramirez & Luco, 1973;Bennett, McLachlan & Taylor, 1973;Grinell & Rheuben, 1979). These neurones normally make synapses with autonomic ganglion cells whose nicotinic ACh receptors differ from those at the neuromuscular junction because they respond differently to certain stimulating and blocking agents.…”