Abstract
We have measured the time intervals (latencies) between the delivery of paired stimuli and the appearance of the extracellularly recorded nerve terminal action potentials (n.a.p.s) and end-plate currents (e.p.c.s) at different temperatures in the sciatic nerve, sartorius muscle preparation of the frog. When the interstimulus interval was 70 ms, the n.a.p. and e.p.c. latencies following the second stimulus of the pair were shorter than following the first at 10°C and 15°C, and facilitation of the e.p.c. was observed. The shortened latency was also observed at 20° C by Barton and Cohen (1982), who suggested that this may be related to facilitation. At 5° C, however, the n.a.p. and e.p.c. latencies following the second stimulus were longer than following the first, and facilitation was still observed. When a 30 ms interstimulus interval was used, the changes in latency were even greater at the temperatures studied.
The changes in e.p.c. latency were due to changes in the conduction velocity of the n.a.p., not changes in synaptic delay. At all temperatures and interstimulus intervals studied, the larger amplitude n.a.p.s were conducted more slowly, however, facilitation was always observed. We conclude that changes in the amplitude and conduction velocity of the nerve action potential do not obviously affect facilitation at the frog neuromuscular junction.
Similar content being viewed by others
References
Baldo GJ (1982) The timing of quantal release during neuromuscular transmission. Ph D Thesis, State University of New York at Stony Brook
Baldo G, Barton SB, Cohen IS, Van der Kloot W (1982) Facilitation and the latency between the stimulus and the nerve terminal action potential at the frog neuromuscular junction. J Physiol 325:87P
Balnave RJ, Gage PW (1977) Facilitation of transmitter secretion from toad motor nerve terminals during brief trains of action potentials. J Physiol 266: 435–451
Barton SB (1977) Facilitation and delayed release of transmitter at the frog neuromuscular junction. D. Phil Thesis, University of Oxford
Barton SB, Cohen IS (1982) Facilitation and impulse propagation failure at the frog neuromuscular junction. Pflügers Arch 392: 327–334
Bullock TS (1951) Facilitation of conduction rate in nerve fibers. J Physiol 114: 89–97
Charlton CP, Bittner GD (1978) Presynaptic action potentials and facilitation of transmitter release in squid giant synapse. J Gen Physiol 72: 487–511
Charlton MP, Smith SJ, Zucker RS (1982) Role of presynaptic calcium ions and channels in synaptic facilitation and depression at the squid synapse. J Physiol 323: 173–193
Dodge FA, Rahamimoff R (1967) Co-operative action of calcium ions in transmitter release at the neuromuscular junction. J Physiol 193: 419–432
Donati F, Kunov H (1967) A model for studying velocity variations in umyelinated axons. IEEE Trans Biomed Eng BME-23: 23–28
Hubbard JI, Schmidt FR (1963) An electrophysiological investigation of mammalian motor nerve terminals. J Physiol 166: 145–167
Katz B, Miledi R (1965a) The measurement of synaptic delay, and the time course of acetylcholine release at the neuromuscular junction. Proc Roy Soc B 161: 483–495
Katz B, Miledi R (1965b) The effect of calcium on acetylcholine release from motor nerve terminals. Proc Roy Soc B 161: 496–503
Katz B, Miledi R (1968) The role of calcium in neuromuscular facilitation. J Physiol 195: 481–492
Miledi R, Slater CR (1966) The action of calcium in neuronal synapses in the squid. J Physiol 184: 473–498
Miller RN, Rinzel J (1981) The dependence of impulse propagation speed on firing frequency, dispersion, for the Hodgkin-Huxley model. Biophys J 34: 227–259
Takeuchi A, Takeuchi N (1962) Electrical changes in the pre- and postsynaptic axons of the giant squid synapse of Loligo. J Gen Physiol 45: 1181–1193
Van der Kloot W, Cohen IS, Attwell D (1980) The timing of ionic channel opening during end-plate currents and the changes responsible for facilitation at the frog neuromuscular junction. Proc XXVIIIth Int Congr Physiol Sci 14: 762
Zucker RS, Lara-Estrella LO (1979) Is synaptic facilitation caused by presynaptic spike broadening. Nature 278: 57–59
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Baldo, G.J., Cohen, I.S. & Van der Kloot, W. Facilitation and the conduction of the nerve action potential at the frog neuromuscular junction. Pflugers Arch. 399, 161–165 (1983). https://doi.org/10.1007/BF00656709
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00656709