Heterosynaptic facilitation of tail sensory neuron synaptic transmission during habituation in tail-induced tail and siphon withdrawal reflexes of Aplysia

Mark Stopfer, Thomas J. Carew

Research output: Contribution to journalArticle

Abstract

In cellular studies of habituation, such as in the gill and siphon withdrawal reflex to tactile stimulation of the siphon of Aplysia, a mechanism that has emerged as an explanation for response decrement during habituation is homosynaptic depression at sensory neurons mediating the behavioral response. We have examined the contribution of homosynaptic depression to habituation in sensory neurons that contribute to two reflex behaviors in Aplysia, tail withdrawal and siphon withdrawal, both elicited by threshold-level tail stimulation. In a companion paper (this issue), we reported that repeated tail stimulation, identical to that producing habituation in siphon withdrawal in freely moving animals, also produces habituation in reduced preparations. In this paper, we extend these behavioral findings by showing that in reduced preparations, identical tail stimulation also produces habituation of the tail withdrawal reflex. In addition, our cellular experiments show that (1) identified sensory and motor neurons in both reflex systems respond to identical repeated tail stimulation; in sensory neurons it produces a progressive decrease in spike number and increase in spike latency, and in motor neurons it produces progressive decrement in complex EPSPs and spike output. (2) Homosynaptic depression of the tail sensory neuron to tail motor neuron synapse does occur when the sensory neurons are activated repetitively by intracellular current. (3) Homosynaptic depression at this synapse does not occur when the sensory neurons are activated repetitively by threshold-level tail stimuli that elicit the behavioral reflex and cause habituation; rather, the sensory neurons exhibit significant heterosynaptic facilitation. Thus, in these reflexes, habituation is not accompanied by homosynaptic depression at the sensory neurons, suggesting that the plasticity underlying habituation occurs primarily at interneuronal sites.

Original languageEnglish (US)
Pages (from-to)4933-4948
Number of pages16
JournalJournal of Neuroscience
Volume16
Issue number16
StatePublished - Aug 15 1996

Fingerprint

Aplysia
Sensory Receptor Cells
Synaptic Transmission
Reflex
Tail
Long-Term Synaptic Depression
Motor Neurons
Synapses
Excitatory Postsynaptic Potentials
Touch

Keywords

  • Aplysia
  • habituation
  • heterosynaptic facilitation
  • homosynaptic depression
  • learning
  • memory

ASJC Scopus subject areas

  • Neuroscience(all)

Cite this

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