The hatchetfish, Gasteropelecus, possesses large pectoral fin adductor muscles whose simultaneous contraction enables the fish to dart upwards at the approach of a predator. These muscles can be excited by either Mauthner fiber. In the medulla, each Mauthner fiber forms axo-axonic synapses on four "giant fibers," two on each side of the midline. Each pair of giant fibers innervates ipsilateral motoneurons controlling the pectoral fin adductor muscles. Mauthner fibers and giant fibers can be penetrated simultaneously by microelectrodes close to the synapses between them. Electrophysiological evidence indicates that transmission from Mauthner to giant fiber is chemically mediated. Under some conditions miniature postsynaptic potentials (PSP's) are observed, suggesting quantal release of transmitter. However, relatively high frequency stimulation reduces PSP amplitude below that of the miniature potentials, but causes no complete failures of PSP's. Thus quantum size is reduced or postsynaptic membrane is desensitized. Ramp currents in Mauthner fibers that rise too slowly to initiate spikes can evoke responses in giant fibers that appear to be asynchronous PSP's. Probably both spikes and ramp currents act on the same secretory mechanism. A single Mauthner fiber spike is followed by prolonged depression of transmission; also PSP amplitude is little affected by current pulses that markedly alter presynaptic spike height. These findings suggest that even a small spike releases most of an immediately available store of transmitter. If so, the probability of release by a single spike is high for any quantum of transmitter within this store.
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1 February 1969
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February 01 1969
Chemically Mediated Transmission at a Giant Fiber Synapse in the Central Nervous System of a Vertebrate
A. A. Auerbach,
A. A. Auerbach
From the Department of Anatomy, Albert Einstein College of Medicine, Bronx, New York 10461, and the Laboratory of Neurophysiology, Department of Neurology, College of Physicians and Surgeons, Columbia University, New York 10032.
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M. V. L. Bennett
M. V. L. Bennett
From the Department of Anatomy, Albert Einstein College of Medicine, Bronx, New York 10461, and the Laboratory of Neurophysiology, Department of Neurology, College of Physicians and Surgeons, Columbia University, New York 10032.
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A. A. Auerbach
From the Department of Anatomy, Albert Einstein College of Medicine, Bronx, New York 10461, and the Laboratory of Neurophysiology, Department of Neurology, College of Physicians and Surgeons, Columbia University, New York 10032.
M. V. L. Bennett
From the Department of Anatomy, Albert Einstein College of Medicine, Bronx, New York 10461, and the Laboratory of Neurophysiology, Department of Neurology, College of Physicians and Surgeons, Columbia University, New York 10032.
The present address of both authors is Department of Anatomy, Albert Einstein College of Medicine, Bronx, New York 10461
Received:
June 20 1968
Online ISSN: 1540-7748
Print ISSN: 0022-1295
Copyright © 1969 by The Rockefeller University Press
1969
J Gen Physiol (1969) 53 (2): 183–210.
Article history
Received:
June 20 1968
Citation
A. A. Auerbach, M. V. L. Bennett; Chemically Mediated Transmission at a Giant Fiber Synapse in the Central Nervous System of a Vertebrate . J Gen Physiol 1 February 1969; 53 (2): 183–210. doi: https://doi.org/10.1085/jgp.53.2.183
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