Proprietà statiche e dinamiche degli EPSPs alla giunzione citoneurale del canale posteriore nel labirinto di rana

A statistical method based on an extension of Campbell's theorem is used to measure the amplitude, waveform and frequency of occurrence of the EPSPs at the cytoneural junction of the posterior canal in the isolated frog labyrinth. This method gives a reliable estimate of the summated and fused EPSP characteristics at rest and during rotation of the canal by measuring the variance, skew and power spectrum of the fluctuations in membrane potential. It can be shown that during rotation the change in EPSP frequency is approximately sinusoidal, indicating a close functional relationship between receptor response and mechanical stimulus. Regression analysis between stimulus and response reveals that the EPSP frequency during excitation and inhibition is, in some units, linearly related to acceleration, while in others it is a linear function of the stimulus logarithm. For accelerations larger than 30 deg/s2 the excitatory response appears to be more consistent than its inhibitory counterpart, and during prolonged and intense stimulation it is also affected by adaptation. The results suggest that many properties of the afferent spike discharge (asymmetry, adaptation, linear or non linear intensity function) are already present in the afferent pathway earlier than at the encoder, and are thus maìnly due to the dynamic characteristics of the afferent synapse