Multiple spike initiation zones in a neuron implicated in learning in the leech: a computational model |
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Authors: | Kevin M Crisp |
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Institution: | (1) Biology Department and Neuroscience Program, St Olaf College, 1520 St Olaf Ave., Northfield, MN 55057, USA |
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Abstract: | Sensitization of the defensive shortening reflex in the leech has been linked to a segmentally repeated tri-synaptic positive
feedback loop. Serotonin from the R-cell enhances S-cell excitability, S-cell impulses cross an electrical synapse into the
C-interneuron, and the C-interneuron excites the R-cell via a glutamatergic synapse. The C-interneuron has two unusual characteristics.
First, impulses take longer to propagate from the S soma to the C soma than in the reverse direction. Second, impulses recorded
from the electrically unexcitable C soma vary in amplitude when extracellular divalent cation concentrations are elevated,
with smaller impulses failing to induce synaptic potentials in the R-cell. A compartmental, computational model was developed
to test the sufficiency of multiple, independent spike initiation zones in the C-interneuron to explain these observations.
The model displays asymmetric delays in impulse propagation across the S–C electrical synapse and graded impulse amplitudes
in the C-interneuron in simulated high divalent cation concentrations. |
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Keywords: | Excitability Divalent cations Electrical coupling Positive feedback SNNAP |
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