Some properties of avian skeletal muscle fibres with multiple neuromuscular junctions

Section: Introductionsupporting

confidence: 84%

Activation of two types of fibres in rat extraocular muscles.

Chiarandini¹

1976

“…Motor axons to the multiply innervated fibres appear to have smaller diameters than the axons to the focally innervated fibres, as revealed by their relatively higher threshold and slower conduction velocity. In all these respects, the synaptic activity of these fibres is similar to that of multiply innervated fibres of frog and avian muscles (Burke, 1957;Ginsborg, 1960) and of cat extraocular muscles (Hess & Pilar, 1963).…”

Section: J Chiarandini and E Stefani Discussionmentioning

confidence: 73%

Electrophysiological identification of two types of fibres in rat extraocular muscles.

Chiarandini¹,

Stefani²

1979

SUMMARY1. The synaptic potentials and electrical properties of rat inferior rectus muscles were examined in vitro.2. In most fibres the spontaneous synaptic activity consisted of typical miniature end-plate potentials which had a normal distribution of amplitudes and rather uniform time courses. Suprathreshold and maximal nerve stimulation evoked unitary end-plate potentials (e.p.p.s). The synaptic activity of these fibres could be recorded only in the innervation zone of the muscle. These fibres were identified as being focally innervated.3. Focally innervated fibres gave action potentials upon direct and indirect stimulation. They had an effective resistance (Reff) of 1'62 + 022 MQ (mean + S.E., twenty-two fibres) and a time constant (Tm) of 3-8 + 04 msec (twenty-one fibres).Voltage-current curves in control saline were linear between membrane potentials of -50 to -140mV. 4. In a small number of fibres the spontaneous synaptic activity consisted of miniature small-nerve junction potentials which had a skewed distribution of amplitudes with predominance of smaller voltages and time courses with a wide range of variation. Nerve stimulation evoked composite small-nerve junction potentials (s.j.p.s) which could be resolved into unitary components by varying the strength of stimulation. S.j.p.s had a higher threshold than e.p.p.s. Synaptic potentials could be recorded outside the innervation zone, at various sites along the muscle length. These fibres were recognized as being multiply innervated with polyneuronal innervation.5. Multiply innervated fibres lacked action potentials, had a large Reff of 6-0 + 1-1 MD (six fibres) and a prolonged Tm of 29-8 + 4*8 msec. Reff show a moderate decrease to hyperpolarization and a rather large decrease to depolarization which denote, respectively, the presence of anomalous and delayed rectification.6. It is concluded that rat extraocular muscles contain at least two populations of muscle fibres that in terms of synaptic activity and electrical properties are comparable to twitch fibres of other mammalian muscles and to slow or tonic fibres of amphibians.

“…For spontaneous reinnervation of the ALD muscle the ALD nerve was cut at the point where it diverges from the PLD nerve. The small branch of the PLD nerve which innervates the ALD muscle (Ginsborg, 1960b) was also cut. When the nerves were severed their central and peripheral stumps retracted so that there was now a gap of 4-5 mm between them.…”

Section: Formation Of Synapses Methodsmentioning

confidence: 99%

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

Bennett¹,

Pettigrew²,

Taylor³

1973

SUMMARY1. A study has been made of the formation of synapses in spontaneously reinnervated and cross-reinnervated anterior latissimus dorsi (ALD) and posterior latissimus dorsi (PLD) muscles of adult fowls.2. Denervated ALD and PLD muscle fibres have a uniform and high sensitivity to iontophoretically applied acetylcholine (ACh). During early reinnervation the sensitivity distribution to ACh of the ALD muscle fibres begins to return to normal before synaptic potentials can be evoked. The normal ACh sensitivity distribution of PLD muscle fibres is also restored after reinnervation. After cross-reinnervation of the ALD and PLD muscles the ACh sensitivity distribution of many of the muscle fibres is again restored to normal.3. Reinnervating and cross-reinnervating ALD nerve terminals showed a greater than normal degree of facilitation of transmitter release when a test impulse was applied at various intervals after a conditioning impulse. Cross-reinnervating PLD nerve terminals showed facilitation of transmitter release rather than the normal depression in a conditioningtest impulse sequence.4. The distribution of nerve terminals over the surface of spontaneously reinnervated and cross-reinnervated ALD and PLD muscle fibres has been determined from an examination of the sensitivity distribution to applied ACh, the graded versus all-or-none nature of the evoked potential and the distribution of cholinesterase stained synapses.5. The results suggest that the innervation pattern of individual ALD and PLD muscle fibres is restored both after spontaneous reinnervation and cross-reinnervation.