Progressive recovery of learning during regeneration of a single synapse in the medicinal leech

Brian D. Burrell, Christie L. Sahley, Kenneth J. Muller

Research output: Contribution to journalArticlepeer-review

30 Scopus citations


The leech escape reflex - shortening of the body - can change with nonassociative conditioning, including sensitization, habituation, and dishabituation. Capacity for sensitization, which is an enhancement of the reflex, is lost when a single S-interneuron is ablated, but the reflex response itself remains. In the present experiments, the S-interneuron's axon in the living leech was filled with 6-carboxyfluorescein (6-CF) dye and cut with an argon laser microbeam (λ = 488 nm). In contrast to sham-operated animals, axotomized preparations did not sensitize, reflecting the key role of the S-cell. By 2 weeks or more, S-cell axons had regenerated and reestablished synapses at their usual locations with neighboring S-cells. By 4 weeks, this restored the ability to sensitize to a level indistinguishable from that of controls, but an intermediate state of recovery was seen from 2-3 weeks after injury - a period not previously examined. The small capacity for sensitization among newly regenerated preparations was significantly lower than in sham controls but appeared higher than in animals whose cut S-cell axon had not regenerated its synapse. The results confirm the crucial role of the S-cell in sensitization. Moreover, full sensitization does not occur immediately upon synapse regeneration.

Original languageEnglish (US)
Pages (from-to)67-74
Number of pages8
JournalJournal of Comparative Neurology
Issue number1
StatePublished - Feb 24 2003
Externally publishedYes


  • Axon regeneration
  • Electrical synapse
  • Laser axotomy
  • Sensitization
  • Synapse regeneration

ASJC Scopus subject areas

  • Neuroscience(all)


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