The transmitter release mechanism was investigated at the cyto-neural junction of the frog labyrinth posterior canal. Low frequency (<100/s) non overlapping EPSP were intracellularly recorded both at rest and during inhibitory mechanical stimulation of the canal (2-8 deg/s2). Recordings were obtained: in control solution; in the presence of increased external Ca2+ (9 mM); in Ca-free EGTA (5 mM) solution and during electrical activation at 50 Hz of the posterior canal inhibitory efferent system. Individual synaptic potentials were digitized and their peak amplitudes, their time intervals as well as the time intervals between them were evaluated. The time intervals proved to be exponentially distributed, suggesting a random EPSP occurrence. The analytical reconstruction of the EPSP waveform indicated that a gamma- function fitted reasonably well both the single and averaged events. As regards the averaged event, despíte the scatter in the values of the gamma-function exponential factor (range 1.1-2.2), in the EPSP time-to-peak (0.6-1.2 ms) and peak amplitude (0.9-2.7 mV) displayed by the units, no significant differences were observed in the same fibre between control and test conditions. Moreover, the event peak amplitude distríbution represented by cumulative plots or amplitude histograms was fitted by a lognormal function. The distributions obtained for the same unit in control solution proved to be not significantly different from those successively obtained under test conditions. The unimodal and continuous EPSP distributions, together with the unvarying characteristics of the single events, strongly suggest that the observed potentials are true mEPSPs due to the release of single quanta of transmitter. Furthermore, the analysis indicates that the quantum size of the elementary event does not change: i) by varying external Ca2+ levels; 2) undèr the influence of the efferent inhibitory transmitter; 3) during the decrease in the afferent transmitter release rate produced by the inhibitory cupula deflection.
Analisi statistica della liberazione di mediatore alla giunzione cito-neurale del canale posteriore nel labirinto isolato di rana
ROSSI, Marialisa;MARTINI, Marta;PELUCCHI, Bruna
1991
Abstract
The transmitter release mechanism was investigated at the cyto-neural junction of the frog labyrinth posterior canal. Low frequency (<100/s) non overlapping EPSP were intracellularly recorded both at rest and during inhibitory mechanical stimulation of the canal (2-8 deg/s2). Recordings were obtained: in control solution; in the presence of increased external Ca2+ (9 mM); in Ca-free EGTA (5 mM) solution and during electrical activation at 50 Hz of the posterior canal inhibitory efferent system. Individual synaptic potentials were digitized and their peak amplitudes, their time intervals as well as the time intervals between them were evaluated. The time intervals proved to be exponentially distributed, suggesting a random EPSP occurrence. The analytical reconstruction of the EPSP waveform indicated that a gamma- function fitted reasonably well both the single and averaged events. As regards the averaged event, despíte the scatter in the values of the gamma-function exponential factor (range 1.1-2.2), in the EPSP time-to-peak (0.6-1.2 ms) and peak amplitude (0.9-2.7 mV) displayed by the units, no significant differences were observed in the same fibre between control and test conditions. Moreover, the event peak amplitude distríbution represented by cumulative plots or amplitude histograms was fitted by a lognormal function. The distributions obtained for the same unit in control solution proved to be not significantly different from those successively obtained under test conditions. The unimodal and continuous EPSP distributions, together with the unvarying characteristics of the single events, strongly suggest that the observed potentials are true mEPSPs due to the release of single quanta of transmitter. Furthermore, the analysis indicates that the quantum size of the elementary event does not change: i) by varying external Ca2+ levels; 2) undèr the influence of the efferent inhibitory transmitter; 3) during the decrease in the afferent transmitter release rate produced by the inhibitory cupula deflection.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
