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.
Modney
B K
BK
Department of Biology, Cleveland State University, Cleveland, Ohio 44115, USA.
Sahley
C L
CL
Muller
K J
KJ
D000818:Animals; D001369:Axons / Q000502:physiology; D001522:Behavior, Animal / Q000502:physiology; D003213:Conditioning, Psychological / Q000502:physiology*; D003714:Denervation; D004594:Electrophysiology; D017952:Ganglia, Invertebrate / Q000166:cytology / Q000502:physiology / Q000601:surgery; D007865:Leeches; D009416:Nerve Regeneration / Q000502:physiology*; D009475:Neurons, Afferent / Q000502:physiology / Q000648:ultrastructure; D012680:Sensitivity and Specificity; D013569:Synapses / Q000502:physiology*