The basic mechanism of transmitter release was investigated at the cytoneural junction of the frog posterior canal by performing a statistical analysis of mEPSPs recorded intracellularly from single fibres of the posterior nerve in the isolated labyrinth. Subthreshold potentials display variable amplitude and it is not immediately clear whether they represent multiquantal events or they are due to the random summation of independent unitary events. Units were examined at rest, during rotation and under the effects of electrical activation of the efferent system. In units with low resting mEPSP frequency (<100/s) and no overlapping of single events, amplitudes and time intervals between successive mEPSPs were measured directly from the tracings. Peak amplitude distributions were countinuous, unimodal and fitted by lognormal distributions while time interval distributions were accurately described by single exponentials. In the presence of higher resting rates and during mechanical stimulation or electrical activation of the facilitatory efferent system (conditions which cause single events to extensively overlap) the mEPSP waveform was estimated by the autoregressive fit to the autocorrelation of the recorded signal and the fit was used to build a Wiener filter for sharpening the original signal. This procedure yielded consistent lognormal peak amplitude distributions at rest as well as during mechanical or efferent stimulation. The interval histograms were monoexponential at rest. A small-sized second peak in amplitude distributions appeared only at the highest mEPSP rates. The area under this peak, corresponding to multiquantal event position, was consistent with the expectation that more than one independent event occurred within the time interval corresponding to the duration of a single event. Results suggest that: 1) mEPSPs are true miniature events, each being due to the release of a single quantum of transmitter by the hair cell; 2) only the rate of transmitter release, but not the elementary quantal mechanism, is affected by rotational stimuli as well as by the modifications in hair celi membrane conductance induced by the efferent transmitter.

SYNAPTIC TRANSMISSION AT THE POSTERIOR CANAL CYTONEURAL JUNCTION IN THE FROG LABYRINTH

ROSSI, Marialisa;MARTINI, Marta;PELUCCHI, Bruna;
1992

Abstract

The basic mechanism of transmitter release was investigated at the cytoneural junction of the frog posterior canal by performing a statistical analysis of mEPSPs recorded intracellularly from single fibres of the posterior nerve in the isolated labyrinth. Subthreshold potentials display variable amplitude and it is not immediately clear whether they represent multiquantal events or they are due to the random summation of independent unitary events. Units were examined at rest, during rotation and under the effects of electrical activation of the efferent system. In units with low resting mEPSP frequency (<100/s) and no overlapping of single events, amplitudes and time intervals between successive mEPSPs were measured directly from the tracings. Peak amplitude distributions were countinuous, unimodal and fitted by lognormal distributions while time interval distributions were accurately described by single exponentials. In the presence of higher resting rates and during mechanical stimulation or electrical activation of the facilitatory efferent system (conditions which cause single events to extensively overlap) the mEPSP waveform was estimated by the autoregressive fit to the autocorrelation of the recorded signal and the fit was used to build a Wiener filter for sharpening the original signal. This procedure yielded consistent lognormal peak amplitude distributions at rest as well as during mechanical or efferent stimulation. The interval histograms were monoexponential at rest. A small-sized second peak in amplitude distributions appeared only at the highest mEPSP rates. The area under this peak, corresponding to multiquantal event position, was consistent with the expectation that more than one independent event occurred within the time interval corresponding to the duration of a single event. Results suggest that: 1) mEPSPs are true miniature events, each being due to the release of a single quantum of transmitter by the hair cell; 2) only the rate of transmitter release, but not the elementary quantal mechanism, is affected by rotational stimuli as well as by the modifications in hair celi membrane conductance induced by the efferent transmitter.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11392/1584465
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