The Journal of Neuroscience, August 1, 2001, 21(15):5781-5793
Synaptic Heterogeneity and Stimulus-Induced Modulation of
Depression in Central Synapses
John D.
Hunter1 and
John G.
Milton1, 2
1 Committee on Neurobiology and
2 Department of Neurology, Committee on Computational
Neuroscience, University of Chicago, Chicago, Illinois 60615
Short-term plasticity is a pervasive feature of synapses. Synapses
exhibit many forms of plasticity operating over a range of time scales.
We develop an optimization method that allows rapid characterization of
synapses with multiple time scales of facilitation and depression.
Investigation of paired neurons that are postsynaptic to the same
identified interneuron in the buccal ganglion of Aplysia
reveals that the responses of the two neurons differ in the magnitude
of synaptic depression. Also, for single neurons, prolonged stimulation
of the presynaptic neuron causes stimulus-induced increases in the
early phase of synaptic depression. These observations can be described
by a model that incorporates two availability factors, e.g., depletable
vesicle pools or desensitizing receptor populations, with different
time courses of recovery, and a single facilitation component. This
model accurately predicts the responses to novel stimuli. The source of
synaptic heterogeneity is identified with variations in the relative
sizes of the two availability factors, and the stimulus-induced
decrement in the early synaptic response is explained by a slowing of
the recovery rate of one of the availability factors. The synaptic
heterogeneity and stimulus-induced modifications in synaptic depression
observed here emphasize that synaptic efficacy depends on both the
individual properties of synapses and their past history.
Key words:
central cholinergic synapses; Aplysia; depletion; desensitization; availability; optimization; model; stimulus
history effects
Copyright © 2001 Society for Neuroscience 0270-6474/01/21155781-13$05.00/0