Miniature excitatoty postsynaptic potentials (mEPSPs) were recorded from single fibres of the posterior nerve during sinusoidal rotations of the semicírcular canal at different frequencies (0.02 to 1 Hz). The mEPSP waveform was estimated by autoregressive analysis of the autocorrelation of post-synaptic potential recordings. The mEPSP mean size and rate of occurrence were determined by means of a procedure of fluctuation analysis devised to continuously monitor these parameters in a rapidly changing system, with a time resolution such that rotation frequencies up to 1 Hz could be studied. The frequency response of synaptic activity was previously shown to be consistent with the hydrodynamic properties of the cupula-endolymph system. Here, we analyse the mEPSP response evoked by successive cycles of rotation. (1) mEPSP rates at the moments of maximum and minimum rotation velocity - 0 acceleration - are higher than resting rates, ie. basal release is potentiated during rotation, paralleling the intensity of the stimulation; (2) the increase in mEPSP rate during the excitatory half cycle is systematically larger than the decreases during the corresponding inhibitory half cycle; (3) the magnitude of all responses often declines with time. In order to obtain hints as to the origin of tbis phenomenon - which was referred to as adaptation - peak and mean mEPSP rates, as well as total release, were computed for each cycle of rotation in each unit at all rotation frequencies. The results confirm that adaptation occurs during maintained rotation and indicate that the magnitude of adaptation is related to peak (or mean) mEPSP rate during the previous cycle, but not to total previous activity. This indicates that the synapse can sustain prolonged release, but it fatigues when maximum release rates have risen particularly high during recent history, suggesting that adaptation does not arise from slow depletion of quantal stores, but rather from the momentary unbalance between the rate of quantal release and the regeneration of the pool of readily releasable quanta.
ADAPTATION OF SYNAPTIC ACTIVTIY DURING SUSTAINED CANAL STIMULATION IN THE FROG LABYIUNTH
ROSSI, Marialisa;BONIFAZZI, Claudio;MARTINI, Marta;PELUCCHI, Bruna;
1997
Abstract
Miniature excitatoty postsynaptic potentials (mEPSPs) were recorded from single fibres of the posterior nerve during sinusoidal rotations of the semicírcular canal at different frequencies (0.02 to 1 Hz). The mEPSP waveform was estimated by autoregressive analysis of the autocorrelation of post-synaptic potential recordings. The mEPSP mean size and rate of occurrence were determined by means of a procedure of fluctuation analysis devised to continuously monitor these parameters in a rapidly changing system, with a time resolution such that rotation frequencies up to 1 Hz could be studied. The frequency response of synaptic activity was previously shown to be consistent with the hydrodynamic properties of the cupula-endolymph system. Here, we analyse the mEPSP response evoked by successive cycles of rotation. (1) mEPSP rates at the moments of maximum and minimum rotation velocity - 0 acceleration - are higher than resting rates, ie. basal release is potentiated during rotation, paralleling the intensity of the stimulation; (2) the increase in mEPSP rate during the excitatory half cycle is systematically larger than the decreases during the corresponding inhibitory half cycle; (3) the magnitude of all responses often declines with time. In order to obtain hints as to the origin of tbis phenomenon - which was referred to as adaptation - peak and mean mEPSP rates, as well as total release, were computed for each cycle of rotation in each unit at all rotation frequencies. The results confirm that adaptation occurs during maintained rotation and indicate that the magnitude of adaptation is related to peak (or mean) mEPSP rate during the previous cycle, but not to total previous activity. This indicates that the synapse can sustain prolonged release, but it fatigues when maximum release rates have risen particularly high during recent history, suggesting that adaptation does not arise from slow depletion of quantal stores, but rather from the momentary unbalance between the rate of quantal release and the regeneration of the pool of readily releasable quanta.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
