Journal of Neuroscience, Vol 5, 2677-2684, Copyright © 1985 by Society for Neuroscience
Synaptic plasticity in the molluscan peripheral nervous system: physiology and role for peptides
CJ Coates and AG Bulloch
The plasticity of a synapse in the molluscan peripheral nervous system was
examined under a variety of experimental, physiological, and
pharmacological conditions. These studies employed the isolated salivary
glands and attached buccal ganglia of the freshwater snail Helisoma. Action
potentials evoked in buccal neuron 4 normally evoke a large excitatory
postsynaptic potential (EPSP) which drives an action potential in gland
secretory cells. In order to measure modulation of the EPSP, action
potential generation in gland cells was prevented by bathing the
preparation in low calcium, high magnesium salines. The relationship
between the gland EPSP amplitude and specific physiological properties of
neuron 4 was analyzed. In common with some central molluscan synapses, the
EPSP was found to be strongly influenced by the membrane potential of
neuron 4. Specifically, its amplitude was reduced by hyperpolarization of
the neuron 4 soma. The relationship between EPSP amplitude and somatic
potential of neuron 4 was linear in the range from resting potential (-47
+/- 6mV) to -100 mV. Furthermore, the EPSP amplitude was directly
proportional to the action potential half-width of neuron 4. In order to
evaluate the possible physiological role of this action potential/EPSP
relationship, we examined whether gland EPSPs are modulated during the
spike broadening that occurs in both spontaneous burst activity and imposed
impulse trains. The preceding action potential/EPSP relationship was
maintained under both of these conditions, i.e., EPSP magnitude increased
as spikes broadened during bursts or trains. The peptidergic modulation of
neuroglandular transmission was also examined. The molluscan peptide SCPB
was found to depolarize neuron 4 and an increase in EPSP amplitude was
concomitantly observed.(ABSTRACT TRUNCATED AT 250 WORDS)
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