mEPSPs were intracellularly recorded in the presence of TTX from single fibres of the posterior nerve at rest and during sinusoídal rotation (0.02-0.5 Hz). To define the frequency response of the cytoneural junction the canal was subjected either to fixed (18 deg.s-2) or increasing peak accelerations (2.5-63 deg.s-2). The mEPSP waveform was evaluated by power spectral analysis; the mEPSP amplitude and rate of occurrence were determined by a fluctuation analysis procedure with a fast time resolution such that rotation frequencles up to 0.5 Hz could be studied. A response asymmetry (increase in mEPSP rate during excitation larger than the corresponding decrease during inhibition) was observed at all rotation frequencies and the time course of the mEPSP rates was analytically well described by asymmetrical sinusoids. For each unit the frequency response was computed in terms of: gain (peak to peak swing in mEPSP rate per unit peak acceleration); phase (phase lead with respect to angular velocity); asymmetry (ratio between excitatory and inhibitory responses). With fixed acceleration the gain vs. frequency relations were systematically described by one-pole low-pass filter functions (corner frequency 0.04-0.24 Hz), in agreement with the kinetics of the cupula-endolymph system. The same behaviour (corner frequency 0.1-0.24 Hz) was exhibited by the units where peak accelerations were changed. When the response of each of these units was corrected for attenuation at the corresponding frequency, linear stimulus-response relations were obtained and a static gain was defined for each unit. Unit phase leads were in agreement with the predictions of the fits obtained from gain data. A decrease in the response to successive cycles of rotation (adaptation) was observed when the EPSP rate during the first cycle exceeded the typical value, strictly related in each unit to its own static gain. No well defined pattems (tuning) could be identified in the fluctuations in EPSP rate at rest or ín the residuals from fits during rotation. These results indicate that most of the properties previously described in the spike firing pattern directly follow from the properties of the transmitter release by the hair cells.
THE SEMICIRCULAR CANAL TRANSFER FUNCTION ANALYZED AT THE mEPSP LEVEL IN THE ISOLATED FROG LABYRINTH
BONIFAZZI, Claudio;MARTINI, Marta;ROSSI, Marialisa
1992
Abstract
mEPSPs were intracellularly recorded in the presence of TTX from single fibres of the posterior nerve at rest and during sinusoídal rotation (0.02-0.5 Hz). To define the frequency response of the cytoneural junction the canal was subjected either to fixed (18 deg.s-2) or increasing peak accelerations (2.5-63 deg.s-2). The mEPSP waveform was evaluated by power spectral analysis; the mEPSP amplitude and rate of occurrence were determined by a fluctuation analysis procedure with a fast time resolution such that rotation frequencles up to 0.5 Hz could be studied. A response asymmetry (increase in mEPSP rate during excitation larger than the corresponding decrease during inhibition) was observed at all rotation frequencies and the time course of the mEPSP rates was analytically well described by asymmetrical sinusoids. For each unit the frequency response was computed in terms of: gain (peak to peak swing in mEPSP rate per unit peak acceleration); phase (phase lead with respect to angular velocity); asymmetry (ratio between excitatory and inhibitory responses). With fixed acceleration the gain vs. frequency relations were systematically described by one-pole low-pass filter functions (corner frequency 0.04-0.24 Hz), in agreement with the kinetics of the cupula-endolymph system. The same behaviour (corner frequency 0.1-0.24 Hz) was exhibited by the units where peak accelerations were changed. When the response of each of these units was corrected for attenuation at the corresponding frequency, linear stimulus-response relations were obtained and a static gain was defined for each unit. Unit phase leads were in agreement with the predictions of the fits obtained from gain data. A decrease in the response to successive cycles of rotation (adaptation) was observed when the EPSP rate during the first cycle exceeded the typical value, strictly related in each unit to its own static gain. No well defined pattems (tuning) could be identified in the fluctuations in EPSP rate at rest or ín the residuals from fits during rotation. These results indicate that most of the properties previously described in the spike firing pattern directly follow from the properties of the transmitter release by the hair cells.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
