Journal of Neuroscience, Vol 7, 1037-1046, Copyright © 1987 by Society for Neuroscience
The probabilistic nature of synaptic transmission at a mammalian excitatory central synapse
B Walmsley, FR Edwards and DJ Tracey
The synaptic connection between single group I afferents and dorsal
spinocerebellar tract (DSCT) neurons in the cat spinal cord has been
studied in an attempt to gain insight into the mechanisms of excitatory
synaptic transmission in the mammalian CNS. Fluctuations in the amplitude
of single group I fiber EPSPs in DSCT neurons were examined using a
numerical deconvolution procedure to reduce the effects of contaminating
noise. In general, it was found that single fiber EPSPs fluctuate in peak
amplitude between discrete levels separated by equal or quantal increments.
Many previous studies have proposed simple binomial statistics as a general
model of quantal synaptic transmission. In the present study we show that
simple binomial statistics do not describe the fluctuations in amplitude of
single group I fiber EPSPs in DSCT neurons. It is suggested that
nonuniformities in the probability of transmitter release from release site
to release site explain the failure of the binomial model to describe the
EPSP fluctuation pattern at this synapse. Nonuniform quantal transmission
is proposed as a more adequate description of excitatory synaptic
transmission in the mammalian CNS.