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The Synapse Between LE Sensory Neurons and Gill Motoneurons Makes Only a Small Contribution to the Aplysia Gill-withdrawal Reflex

Authors

  • Christopher Hickie,

    1. Department of Cellular and Molecular Physiology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06510, USA
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    • 3

      School of Medicine, University of Connecticut Health Center, Farmington, CT, USA

  • Lawrence B. Cohen,

    Corresponding author
    1. Department of Cellular and Molecular Physiology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06510, USA
    • Correspondence to: Lawrence B. Cohen, as above

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  • Pavel M. Balaban

    1. Institute of Higher Nervous Activity and Neurophysiology, 117865 Moscow, Russia
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Abstract

The monosynaptic connection between the mechano-sensory neurons in the LE cluster and gill motoneurons has been extensively studied and used as a model for the gill-withdrawal reflex and its behavioural plasticity. In an attempt to evaluate the contribution of this synapse to the behaviour, we used voltage-sensitive dye recording to determine the number of activated LE neurons and the number of spikes made by each neuron in response to a light touch. In five preparations, light touch activated a median of five sensory cells with a median of 1.6 spikes per cell. From a comparison of the sizes of the motoneuron synaptic potentials elicited by LE spikes and elicited by a light siphon touch, we estimate that the LE sensory neurons contribute ˜5% of the motoneuron synaptic potential in response to this touch. This result casts doubt on the validity of using this synaptic connection as a model for gill-withdrawal behaviour. Siphon nerve recordings reveal the existence of short-latency, low-threshold neurons that may provide much of the sensory input in response to a light touch.

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