Regeneration of a central synapse restores nonassociative learning

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.

Abstract sourced from PubMed (NCBI) for the cited record. See the original publication for the authoritative version.

In Hirudo medicinalis, surgically separating the S-interneuron from its synaptic partner abolishes sensitization (a form of nonassociative learning); synaptic regeneration restores the behavior — directly linking a single synapse to a learned behavior.

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