Localization of sites where abnormal miniature end-plate currents arise at the myoneural junction
Frog cutaneous-sternal muscle preparations were used to examine mechanisms by which extracellularly recorded abnormal miniature postsynaptic signals are generated. The frequency of these signals was found to increase after denervation as well as after the addition of 4-aminoquinolinic acid (0.25 mmol/liter) and emetine (10 mmol/liter) to the solution perfusing the preparation. Graphic delineation, using a 3-electrode technique, of the sites where signals were arising in the nerve terminal showed that neurotransmitter (acetylcholine) quanta responsible for the generation of postsynaptic signals emerged in limited areas of the myoneural junction between terminal portions of the active zones instead of being released from the latter. It is concluded that the source of such quanta is most likely to be the Schwann cell and that the mechanism via which the neurotransmitter is released from this cell is distinct from the mechanism of its release from the nerve terminal.
Key Wordsmyoneural junction abnormal miniature signals Schwann cell active zone
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