EPSPs intracellularly recorded from single fibers of the posterior nerve show different resting frequencies (10-300/s). To study the transmitter release mechanism in units with low resting rates (<100/s) as well as under experimental conditions that decrease the spontaneous frequency (mechanical inhibition or activation of the inhibitory efferent system), peak amplitudes and time intervals between events were directly measured in the tracings. Peak amplitude histograms were continuous, unimodal and well fitted by lognormal functions; time interval distributions were monoexponentiaL In the presence of high EPSP rates at rest, or when the transmitter release was enhanced by mechanical excitation or by activation of the facilitatorv efferent system, single events extensively overlap and show a highly variable size. In these conditions direct evaluation of time intervals yielded histograms lacking short values and peak amplitudes showed a marked skewness toward high values while their distribution was described by the sum of two or more lognormal functions. The analysis was improved to define whether at high rates the junction releases multiquantal events multiple of the elementary size. The EPSP waveform was estimated by autoregressive fit to the autocorrelation of the recorded signal and the fit was used to build a Wiener filter for sharpening the original signal before computing new time interval and peak amplitude histograms. This procedure yielded consistent lognormal peak amplitude distributions and monoexponential time intervals similar to those obtained at low resting rates. Results suggest that 1) EPSPs are true miniature events, due to the random summation of independently occurring unitary events, which overlap at high frequencies; 2) no giant mEPSPs occur at the cytoneural junction; 3) the rate of transmitter release, but not its basic mechanism (which remains asynchronous) is affected by rotational stimulation as well as by the modifications in hair cell membrane conductance induced by the efferent transmitters.
THE QUANTAL NATURE OF TRANSMITTER RELEASE AT THE CYTONEURAL JUNCTION OF THE FROG LABYRINTH
ROSSI, Marialisa;MARTINI, Marta;PELUCCHI, Bruna;
1993
Abstract
EPSPs intracellularly recorded from single fibers of the posterior nerve show different resting frequencies (10-300/s). To study the transmitter release mechanism in units with low resting rates (<100/s) as well as under experimental conditions that decrease the spontaneous frequency (mechanical inhibition or activation of the inhibitory efferent system), peak amplitudes and time intervals between events were directly measured in the tracings. Peak amplitude histograms were continuous, unimodal and well fitted by lognormal functions; time interval distributions were monoexponentiaL In the presence of high EPSP rates at rest, or when the transmitter release was enhanced by mechanical excitation or by activation of the facilitatorv efferent system, single events extensively overlap and show a highly variable size. In these conditions direct evaluation of time intervals yielded histograms lacking short values and peak amplitudes showed a marked skewness toward high values while their distribution was described by the sum of two or more lognormal functions. The analysis was improved to define whether at high rates the junction releases multiquantal events multiple of the elementary size. The EPSP waveform was estimated by autoregressive fit to the autocorrelation of the recorded signal and the fit was used to build a Wiener filter for sharpening the original signal before computing new time interval and peak amplitude histograms. This procedure yielded consistent lognormal peak amplitude distributions and monoexponential time intervals similar to those obtained at low resting rates. Results suggest that 1) EPSPs are true miniature events, due to the random summation of independently occurring unitary events, which overlap at high frequencies; 2) no giant mEPSPs occur at the cytoneural junction; 3) the rate of transmitter release, but not its basic mechanism (which remains asynchronous) is affected by rotational stimulation as well as by the modifications in hair cell membrane conductance induced by the efferent transmitters.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
