Temporal Dynamics of Graded Synaptic Transmission in
the Lobster Stomatogastric Ganglion.
Yair Manor, Farzan Nadim, L.F. Abbott and Eve Marder.
Abstract
Synaptic transmission between neurons in the stomatogastric ganglion of the lobster Panulirus
interruptus is a graded function of membrane potential, with a threshold for
transmitter release in the range of -50 to -60 mV. We studied the dynamics of graded
transmission between the lateral pyloric (LP) neuron and the pyloric dilator (PD) neurons
after blocking action potential-mediated transmission with 0.1 micromolar tetrodotoxin. We
compared the graded IPSPs (gIPSPs) from LP to PD neurons evoked by square pulse
presynaptic depolarizations with those potentials evoked by realistic presynaptic
waveforms of variable frequency, amplitude and duty cycle. The gIPSP shows
frequency-dependent synaptic depression. The recovery from depression is slow, and as a
result, the gIPSP is depressed at normal pyloric network frequencies. Changes in the
duration of the presynaptic depolarization produce nonintuitive changes in the amplitude
and time-course of the postsynaptic responses, which are again frequency-dependent. Taken
together, these data demonstrate that the measurements of synaptic efficacy that are used
to understand neural network function are best made using presynaptic waveforms and
patterns of activity that mimic those in the functional network.
