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Volume 17, Number 16,
Issue of August 15, 1997
pp. 6478-6482
Copyright ©1997 Society for Neuroscience
Regeneration of a Central Synapse Restores Nonassociative
Learning
Received April 8, 1997; revised June 2, 1997; accepted June 2, 1997.
Barbara K. Modney1,
Christie L. Sahley2, and
Kenneth J. Muller3
1 Department of Biology, Cleveland State University,
Cleveland, Ohio 44115, 2 Department of Biological Sciences,
Purdue University, West Lafayette, Indiana 47907, and
3 Department of Physiology and Biophysics, University of
Miami School of Medicine, Miami, Florida 33136
Sensitization is a form of nonassociative learning in which a
strong or noxious stimulus persistently enhances the response produced
by a weaker stimulus. In the leech Hirudo medicinalis, the S-interneuron is required for sensitization of the shortening response. A single S-cell axon was surgically separated from its sole
synaptic partner, the neighboring S-cell. This consistently eliminated
sensitization without impairing reflexive shortening itself, as
measured in semi-intact specimens. Sensitization of the shortening
reflex returned after 3 weeks when the severed axon grew and
regenerated its specific electrical synapse within the nerve cord, as
shown by restored conduction of impulses between S-cells. This confirms
the essential role of one neuron, the S-cell, in sensitization, and it
demonstrates that regeneration of the synapse between S-cells restores
this example of nonassociative learning.
Key words:
invertebrate learning;
leech;
regeneration;
nerve repair;
nonassociative conditioning;
plasticity;
axotomy;
Hirudo
medicinalis;
S-cell;
synapse regeneration
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