EPSPs vere intra-axonally recorded from single fibres of the posterior nerve in the isolated frog labyrinth. Recordings were obtained at rest as well as under electrical activation (50Hz) of the posterior canal inhibitory efferent system. Resting and stimulated fibres were tested in: 1) control solution; 2) in the presence of raised extracellular Ca2+ (9 mM); 3) Ca-free EGTA (5 mM) solution. Only afferent units where the resting EPSP emission rate was low enough (<100/s) to prevent the overlapping of single EPSPs were analyzed. Synaptic potential were digitized and their peak amplitude as well as the time intervals between them were evaluated. Time intervals were exponentially distributed, suggestive of a rendom occurrence of EPSPs. A large number of EPSPs (200-800) were computed in single units under each experimental condition. The event distributions, represented in cumulative plots or amplitude histograms, were reasonably well fitted by lognormal functions. The distributions successively obtained in different ionic media from the same unit were compared by a non parametric test and proved to be not significantly different. Unimodal and continuous distributions of EPSP peak values indicate that: l) the observed synaptic potentials are most likely true mEPSPs each being due to the release of a single quantum of transmitter; 2) the efferent inhibitory synapse decreases the mEPSP frequency but does not reduce the quantum size; 3) the resting afferent transmitter release mechanism is unaffected by external Ca2+ levels.
STATISTICAL ANALYSIS OF EPSP OCCURRENCE AT THE CYTO-NEURAL JUNCTION IN THE FROG LABYRINTH
ROSSI, Marialisa;MARTINI, Marta;PELUCCHI, Bruna
1992
Abstract
EPSPs vere intra-axonally recorded from single fibres of the posterior nerve in the isolated frog labyrinth. Recordings were obtained at rest as well as under electrical activation (50Hz) of the posterior canal inhibitory efferent system. Resting and stimulated fibres were tested in: 1) control solution; 2) in the presence of raised extracellular Ca2+ (9 mM); 3) Ca-free EGTA (5 mM) solution. Only afferent units where the resting EPSP emission rate was low enough (<100/s) to prevent the overlapping of single EPSPs were analyzed. Synaptic potential were digitized and their peak amplitude as well as the time intervals between them were evaluated. Time intervals were exponentially distributed, suggestive of a rendom occurrence of EPSPs. A large number of EPSPs (200-800) were computed in single units under each experimental condition. The event distributions, represented in cumulative plots or amplitude histograms, were reasonably well fitted by lognormal functions. The distributions successively obtained in different ionic media from the same unit were compared by a non parametric test and proved to be not significantly different. Unimodal and continuous distributions of EPSP peak values indicate that: l) the observed synaptic potentials are most likely true mEPSPs each being due to the release of a single quantum of transmitter; 2) the efferent inhibitory synapse decreases the mEPSP frequency but does not reduce the quantum size; 3) the resting afferent transmitter release mechanism is unaffected by external Ca2+ levels.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
