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. 1976 Jul;259(2):367–393. doi: 10.1113/jphysiol.1976.sp011471

Synaptic depression related to presynaptic axon conduction block.

H Hatt, D O Smith
PMCID: PMC1309034  PMID: 182964

Abstract

1. The depression of synaptic transmission, which occurs during prolonged repetitive activation, was examined in the opener muscle of the crayfish walking leg. 2. Excitatory post-synaptic potentials (e.p.s.p.s) initially facilitated but then declined to low amplitudes after about 4000 stimulus pulses had been delivered; this depression is presynaptic in origin; 3. Axon conduction blocks occured at points of bifurcation along the entire length of the presynaptic nerve. This resulted in failure of the nerve impulse to invade some branches of the terminal arborization. 4. Nerve terminal invasion failure caused either intermittent or complete inactiviation of some synaptic release sites; this was associated with depression of the post-synaptic response. 5. The statistics of transmitter release during prolonged repetitive stimulation were examined by focal extracellular recording methods. Transmitter release could be described by binomial statistics, and depression involved a drop in m, n and p. 6. The rate of spontaneous quantal release did not decrease, however, arguing against transmitter depletion. 7. It is concluded that repetitive stimulation eventually leads to depolarization of the axon membrane. This causes impulse propagation failure which reduces the number of synaptic release sites that are activated and mimics a drop in the effective stimulation rate; both effects cause synaptic depression.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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