The mechanism of acetylcholine release has been studied by intracellular recordings in isolated preparations of the guinea-pig superior cervical ganglion. EPSPs were recorded following repetitive stimulation of a single afferent pre-ganglionic fibre at different frequencies. It was possible to elicit subthreshold responses from the majority of the impaled cells in the absence of any modification of Ca++ and Mg++ concentrations in the incubating medium. Transmitter release was found to be quantal in nature and EPSP amplitudes were shown to fluctuate in quantal steps in accordance with Poisson's law. Quantum content, as evaluated from 26 analyses carried out in 13 nerve cells, was a mean of 1.5. This low output of acetylcholine is tentatively related to the limited number of terminal knobs given to single neurons by each pre-ganglionic fibre and the restricted total area of the synaptic contacts. Quantum content appears to depend little on the stimulation frequency in the range of 1-10/sec, except in individual cases. The release of some 13 quanta, corresponding to the simultaneous activation of 8 pre-ganglionic converging fibres is estimated to be necessary to drive the ganglion neurons up to their firing threshold. © 1971 Springer-Verlag.
The mechanism of acetylcholine release has been studied by intracellular recordings in isolated preparations of the guinea-pig superior cervical ganglion. EPSPs were recorded following repetitive stimulation of a single afferent pre-ganglionic fibre at different frequencies. It was possible to elicit subthreshold responses from the majority of the impaled cells in the absence of any modification of Ca++and Mg++concentrations in the incubating medium. Transmitter release was found to be quantal in nature and EPSP amplitudes were shown to fluctuate in quantal steps in accordance with Poisson's law. Quantum content, as evaluated from 26 analyses carried out in 13 nerve cells, was a mean of 1.5. This low output of acetylcholine is tentatively related to the limited number of terminal knobs given to single neurons by each pre-ganglionic fibre and the restricted total area of the synaptic contacts. Quantum content appears to depend little on the stimulation frequency in the range of 1-10/sec, except in individual cases. The release of some 13 quanta, corresponding to the simultaneous activation of 8 pre-ganglionic converging fibres is estimated to be necessary to drive the ganglion neurons up to their firing threshold. © 1971 Springer-Verlag.
Quantal release of acetylcholine from the nerve endings of the guinea-pig superior cervical ganglion
SACCHI, Oscar;PERRI, Virgilio
1971
Abstract
The mechanism of acetylcholine release has been studied by intracellular recordings in isolated preparations of the guinea-pig superior cervical ganglion. EPSPs were recorded following repetitive stimulation of a single afferent pre-ganglionic fibre at different frequencies. It was possible to elicit subthreshold responses from the majority of the impaled cells in the absence of any modification of Ca++and Mg++concentrations in the incubating medium. Transmitter release was found to be quantal in nature and EPSP amplitudes were shown to fluctuate in quantal steps in accordance with Poisson's law. Quantum content, as evaluated from 26 analyses carried out in 13 nerve cells, was a mean of 1.5. This low output of acetylcholine is tentatively related to the limited number of terminal knobs given to single neurons by each pre-ganglionic fibre and the restricted total area of the synaptic contacts. Quantum content appears to depend little on the stimulation frequency in the range of 1-10/sec, except in individual cases. The release of some 13 quanta, corresponding to the simultaneous activation of 8 pre-ganglionic converging fibres is estimated to be necessary to drive the ganglion neurons up to their firing threshold. © 1971 Springer-Verlag.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
