Journal of Neuroscience, Vol 9, 840-850, Copyright © 1989 by Society for Neuroscience
Amplitude fluctuations in small EPSPs recorded from CA1 pyramidal cells in the guinea pig hippocampal slice
RJ Sayer, SJ Redman and P Andersen
Experimental Neurology Unit, John Curtin School of Medical Research, Australian National University, Canberra.
EPSPs have been evoked in CA1 pyramidal cells by (1) activation of single
CA3 neurons (unitary EPSPs), and (2) low-intensity stimuli to the CA1
stratum radiatum. Five unitary EPSPs were obtained; their mean peak
amplitudes ranged from 85 to 275 microV and 3 of the 5 showed fluctuations
in amplitude that were too great to be attributed to baseline noise. After
subtraction of the variance due to the noise, these EPSPs had coefficients
of variation much higher than those reported for variability in the quantal
EPSP in other preparations. These results suggest that intermittent
transmitter release is a major cause of EPSP amplitude fluctuation at this
synapse. A noise deconvolution technique based on a nonrestrictive model of
transmitter release was applied to the EPSPs obtained in this study. For 2
of the EPSPs evoked by stratum radiatum stimulation, the amplitudes
fluctuated between discrete values that were sufficiently separated with
respect to the noise to be resolved by the deconvolution procedure. Quantal
increments of 224 and 193 microV were determined for the 2 EPSPs.