The EPSP rate was intracellularly recorded from single fibres of the posterior nerve in the isolated frog labyrinth. Recordings were performed at rest and during sinusoidal canal rotation in the presence of TTX to prevent afferent spike discharge. At rest, the EPSPs are released at a considerably high rate (70-400 EPSPs/s) and their frequency consistently increases during excitation. This fact leads to a high degree of EPSP summation and fusion. To obtain a reliable estimate of both amplitude and frequency of the single EPSPs at rest and during rotation a statistical method measuring the variance, skewness and power spectrum of the fluctuations in the postsynaptic membrane potential was applied. It was observed that during rotation the change in EPSP frequency is approximately sinusoidal, indicating a dose functional relationship between stimulus and receptor response. The EPSP peak firing level during excitation and inhibition proved in some units to be linearly related to the stimulus intensity while in others it was a linear function of the stimulus logarithm. The excitatory response was larger than its inhibitory counterpart and also affected by adaptation. The present results suggest that many properties of the spike response (asymmetry, adaptation, linear or non linear intensity function) are already present in the afferent pathway earlier than at the encoder and are thus mainly due to the dynamic characteristics of the afferent synapse.
EPSP DISCHARGE PROPERTIES AT THE AFFERENT SYNAPSE OF THE FROG LABYRINTH POSTERIOR CANAL
ROSSI, Marialisa;BONIFAZZI, Claudio;MARTINI, Marta;
1988
Abstract
The EPSP rate was intracellularly recorded from single fibres of the posterior nerve in the isolated frog labyrinth. Recordings were performed at rest and during sinusoidal canal rotation in the presence of TTX to prevent afferent spike discharge. At rest, the EPSPs are released at a considerably high rate (70-400 EPSPs/s) and their frequency consistently increases during excitation. This fact leads to a high degree of EPSP summation and fusion. To obtain a reliable estimate of both amplitude and frequency of the single EPSPs at rest and during rotation a statistical method measuring the variance, skewness and power spectrum of the fluctuations in the postsynaptic membrane potential was applied. It was observed that during rotation the change in EPSP frequency is approximately sinusoidal, indicating a dose functional relationship between stimulus and receptor response. The EPSP peak firing level during excitation and inhibition proved in some units to be linearly related to the stimulus intensity while in others it was a linear function of the stimulus logarithm. The excitatory response was larger than its inhibitory counterpart and also affected by adaptation. The present results suggest that many properties of the spike response (asymmetry, adaptation, linear or non linear intensity function) are already present in the afferent pathway earlier than at the encoder and are thus mainly due to the dynamic characteristics of the afferent synapse.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
