To study the transmitter release mechanism at the posterior canal cyto-neural junction, low frequency (<100/s) non overlapping mEPSPs were recorded from single afferent fibres in the isolated frog labyrinth. The mEPSPs were then digitized and the peak values as well as the time integrals of a large number of spontaneous events were computed from recordings performed in: 1) control solution; 2) high extracellular Ca2+(9mM); 3) Ca-free EGTA (5 mM) solution. The analysis was then extended to tracings obtained: 1) during inhibitory acceleratory steps (2-8 deg/s2) applied to the canal by means of a turn-table; 2) under electrical activation of the posterior canal inhibitory efferent system. For each unit single and averaged potentials (mean of 25-100 events) in control solution were compared to those observed in at least one of the test conditions. The analytical reconstruction of the mEPSP waveform indicated that a gamma function provides a reasonable good fit both to single and averaged events. Similar values of the exponential factor in the gamma function (range 1.14-2.22) vere obtained from control and test experiments in the same unit, thus indicating that no systematic modifications in cable properties had ensued. Moreover, despite the scatter in mEPSP time-to-peak (range 0.66-1.17 ms) and peak amplitude values (range 0.96-2.69 mV), no significant differences were observed between control and test conditions. Previous experiments have shown that peak mEPSP amplitudes are well fitted by similar lognormal distribution functions in control and test experiments, thus suggesting that the quantum size of the elementary event did not change. This analysis of the mEPSP characteristics thus confirms that the basic mechanism of transmitter release is independent of: 1) external calcium levels; 2) modifications in the hair celi conductance during the action of the efferent transmitter; 3) decrease in the afferent transmitter release by cupula deflections in the inhibitory direction.
MEPSP PROPERTIES AT THE POSTERIOR CANAL CYTO-NEURAL JUNCTION
ROSSI, Marialisa;MARTINI, Marta;PELUCCHI, Bruna
1991
Abstract
To study the transmitter release mechanism at the posterior canal cyto-neural junction, low frequency (<100/s) non overlapping mEPSPs were recorded from single afferent fibres in the isolated frog labyrinth. The mEPSPs were then digitized and the peak values as well as the time integrals of a large number of spontaneous events were computed from recordings performed in: 1) control solution; 2) high extracellular Ca2+(9mM); 3) Ca-free EGTA (5 mM) solution. The analysis was then extended to tracings obtained: 1) during inhibitory acceleratory steps (2-8 deg/s2) applied to the canal by means of a turn-table; 2) under electrical activation of the posterior canal inhibitory efferent system. For each unit single and averaged potentials (mean of 25-100 events) in control solution were compared to those observed in at least one of the test conditions. The analytical reconstruction of the mEPSP waveform indicated that a gamma function provides a reasonable good fit both to single and averaged events. Similar values of the exponential factor in the gamma function (range 1.14-2.22) vere obtained from control and test experiments in the same unit, thus indicating that no systematic modifications in cable properties had ensued. Moreover, despite the scatter in mEPSP time-to-peak (range 0.66-1.17 ms) and peak amplitude values (range 0.96-2.69 mV), no significant differences were observed between control and test conditions. Previous experiments have shown that peak mEPSP amplitudes are well fitted by similar lognormal distribution functions in control and test experiments, thus suggesting that the quantum size of the elementary event did not change. This analysis of the mEPSP characteristics thus confirms that the basic mechanism of transmitter release is independent of: 1) external calcium levels; 2) modifications in the hair celi conductance during the action of the efferent transmitter; 3) decrease in the afferent transmitter release by cupula deflections in the inhibitory direction.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
